Publications by authors named "Siddharth Banka"

91 Publications

100,000 Genomes Pilot on Rare-Disease Diagnosis in Health Care - Preliminary Report.

N Engl J Med 2021 11;385(20):1868-1880

From Genomics England (D.S., K.R.S., A.M., E.A.T., E.M.M., A.T., G.C., K.I., L.M., M. Wielscher, A.N., M. Bale, E.B., C.B., H.B., M. Bleda, A. Devereau, D.H., E. Haraldsdottir, Z.H., D.K., C. Patch, D.P., A.M., R. Sultana, M.R., A.L.T.T., C. Tregidgo, C. Turnbull, M. Welland, S. Wood, C.S., E.W., S.L., R.E.F., L.C.D., O.N., I.U.S.L., C.F.W., J.C., R.H.S., T.F., A.R., M.C.), the William Harvey Research Institute, Queen Mary University of London (D.S., K.R.S., V.C., A.T., L.M., M.R.B., D.K., S. Wood, P.C., J.O.J., T.F., M.C.), University College London (UCL) Institute of Ophthalmology (V.C., G.A., M.M., A.T.M., S. Malka, N.P., P.Y.-W.-M., A.R.W.), UCL Genetics Institute (V.C., N.W.W.), GOSgene (H.J.W.), Genetics and Genomic Medicine Programme (L.V., M.R., M.D., L.C., P. Beales, M.B.-G.), National Institute for Health Research (NIHR) Great Ormond Street Hospital Biomedical Research Centre (BRC) (M.R., S. Grunewald, S.C.-L., F.M., C. Pilkington, L.R.W., L.C., P. Beales, M.B.-G.), Infection, Immunity, and Inflammation Research and Teaching Department (P.A., L.R.W.), Stem Cells and Regenerative Medicine (N.T.), and Mitochondrial Research Group (S. Rahman), UCL Great Ormond Street Institute of Child Health, UCL Ear Institute (L.V.), the Department of Renal Medicine (D. Bockenhauer), and Institute of Cardiovascular Science (P.E.), UCL, Moorfields Eye Hospital National Health Service (NHS) Foundation Trust (V.C., G.A., M.M., A.T.M., S. Malka, N.P., A.R.W.), the National Hospital for Neurology and Neurosurgery (J.V., E.O., J.Y., K. Newland, H.R.M., J.P., N.W.W., H.H.), the Metabolic Unit (L.A., S. Grunewald, S. Rahman), London Centre for Paediatric Endocrinology and Diabetes (M.D.), and the Department of Gastroenterology (N.T.), Great Ormond Street Hospital for Children NHS Foundation Trust (L.V., D. Bockenhauer, A. Broomfield, M.A.C., T. Lam, E.F., V.G., S.C.-L., F.M., C. Pilkington, R. Quinlivan, C.W., L.R.W., A. Worth, L.C., P. Beales, M.B.-G., R.H.S.), the Clinical Genetics Department (M.R., T.B., C. Compton, C.D., E. Haque, L.I., D.J., S. Mohammed, L.R., S. Rose, D.R., G.S., A.C.S., F.F., M.I.) and St. John's Institute of Dermatology (H.F., R. Sarkany), Guy's and St. Thomas' NHS Foundation Trust, the Division of Genetics and Epidemiology, Institute of Cancer Research (C. Turnbull), Florence Nightingale Faculty of Nursing, Midwifery, and Palliative Care (T.B.), Division of Genetics and Molecular Medicine (M.A.S.), and Division of Medical and Molecular Genetics (M.I.), King's College London, NIHR BRC at Moorfields Eye Hospital (P.Y.-W.-M.), NHS England and NHS Improvement, Skipton House (V.D., A. Douglas, S. Hill), and Imperial College Healthcare NHS Trust, Hammersmith Hospital (K. Naresh), London, Open Targets and European Molecular Biology Laboratory-European Bioinformatics Institute, Wellcome Genome Campus, Hinxton (E.M.M.), the Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine, and Health, University of Manchester (J.M.E., S.B., J.C.-S., S.D., G.H., H.B.T., R.T.O., G. Black, W.N.), and the Manchester Centre for Genomic Medicine, St. Mary's Hospital, Manchester University NHS Foundation Trust (J.M.E., Z.H., S.B., J.C.-S., S.D., G.H., G. Black, W.N.), Manchester, the Department of Genetic and Genomic Medicine, Institute of Medical Genetics, Cardiff University, Cardiff (H.J.W.), the Department of Clinical Neurosciences (T.R., W.W., R.H., P.F.C.), the Medical Research Council (MRC) Mitochondrial Biology Unit (T.R., W.W., P.Y.-W.-M., P.F.C.), the Department of Paediatrics (T.R.), the Department of Haematology (K.S., C. Penkett, S. Gräf, R.M., W.H.O., A.R.), the School of Clinical Medicine (K.R., E.L., R.A.F., K.P., F.L.R.), the Department of Medicine (S. Gräf), and Cambridge Centre for Brain Repair, Department of Clinical Neurosciences (P.Y.-W.-M.), University of Cambridge, NIHR BioResource, Cambridge University Hospitals (K.S., S.A., R.J., C. Penkett, E.D., S. Gräf, R.M., M.K., J.R.B., P.F.C., W.H.O., F.L.R.), and Addenbrooke's Hospital, Cambridge University Hospitals NHS Foundation Trust (G.F., P.T., O.S.-B., S. Halsall, K.P., A. Wagner, S.G.M., N.B., M.K.), Cambridge Biomedical Campus, Wellcome-MRC Institute of Metabolic Science and NIHR Cambridge BRC (M.G.), Congenica (A.H., H.S.), Illumina Cambridge (A. Wolejko, B.H., G. Burns, S. Hunter, R.J.G., S.J.H., D. Bentley), NHS Blood and Transplant (W.H.O.), and Wellcome Sanger Institute (W.H.O.), Cambridge, the Health Economics Research Centre (J. Buchanan, S. Wordsworth) and the Wellcome Centre for Human Genetics (C. Camps, J.C.T.), University of Oxford, NIHR Oxford BRC (J. Buchanan, S. Wordsworth, J.D., C. Crichton, J.W., K.W., C. Camps, S.P., N.B.A.R., A.S., J.T., J.C.T.), the Oxford Centre for Genomic Medicine (A. de Burca, A.H.N.), and the Departments of Haematology (N.B.A.R.) and Neurology (A.S.), Oxford University Hospitals NHS Foundation Trust, Oxford Genetics Laboratories, Oxford University Hospitals NHS Foundation Trust, Churchill Hospital (C. Campbell, K.G., T. Lester, J.T.), the MRC Weatherall Institute of Molecular Medicine (N.K., N.B.A.R., A.O.M.W.) and the Oxford Epilepsy Research Group (A.S.), Nuffield Department of Clinical Neurosciences (A.H.N.), University of Oxford, and the Department of Clinical Immunology (S.P.), John Radcliffe Hospital, Oxford, Peninsula Clinical Genetics Service, Royal Devon and Exeter NHS Foundation Trust (E.B.), and the University of Exeter Medical School (E.B., C.F.W.), Royal Devon and Exeter Hospital (S.E.), Exeter, Newcastle Eye Centre, Royal Victoria Infirmary (A.C.B.), the Institute of Genetic Medicine, Newcastle University, International Centre for Life (V.S., P. Brennan), Wellcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University (G.S.G., R.H., A.M.S., D.M.T., R. Quinton, R.M., R.W.T., J.A.S.), Highly Specialised Mitochondrial Service (G.S.G., A.M.S., D.M.T., R.M., R.W.T.) and Northern Genetics Service (J. Burn), Newcastle upon Tyne Hospitals NHS Foundation Trust (J.A.S.), and NIHR Newcastle BRC (G.S.G., D.M.T., J.A.S.), Newcastle upon Tyne, the Institute of Cancer and Genomic Sciences, Institute of Biomedical Research, University of Birmingham (C. Palles), and Birmingham Women's Hospital (D.M.), Birmingham, the Genomic Informatics Group (E.G.S.), University Hospital Southampton (I.K.T.), and the University of Southampton (I.K.T.), Southampton, Liverpool Women's NHS Foundation Trust, Liverpool (A. Douglas), the School of Cellular and Molecular Medicine, University of Bristol, Bristol (A.D.M.), and Yorkshire and Humber, Sheffield Children's Hospital, Sheffield (G.W.) - all in the United Kingdom; Fabric Genomics, Oakland (M. Babcock, M.G.R.), and the Ophthalmology Department, University of California, San Francisco School of Medicine, San Francisco (A.T.M.) - both in California; the Jackson Laboratory for Genomic Medicine, Farmington, CT (P.N.R.); and the Center for Genome Research and Biocomputing, Environmental and Molecular Toxicology, Oregon State University, Corvallis (M.H.).

Background: The U.K. 100,000 Genomes Project is in the process of investigating the role of genome sequencing in patients with undiagnosed rare diseases after usual care and the alignment of this research with health care implementation in the U.K. National Health Service. Other parts of this project focus on patients with cancer and infection.

Methods: We conducted a pilot study involving 4660 participants from 2183 families, among whom 161 disorders covering a broad spectrum of rare diseases were present. We collected data on clinical features with the use of Human Phenotype Ontology terms, undertook genome sequencing, applied automated variant prioritization on the basis of applied virtual gene panels and phenotypes, and identified novel pathogenic variants through research analysis.

Results: Diagnostic yields varied among family structures and were highest in family trios (both parents and a proband) and families with larger pedigrees. Diagnostic yields were much higher for disorders likely to have a monogenic cause (35%) than for disorders likely to have a complex cause (11%). Diagnostic yields for intellectual disability, hearing disorders, and vision disorders ranged from 40 to 55%. We made genetic diagnoses in 25% of the probands. A total of 14% of the diagnoses were made by means of the combination of research and automated approaches, which was critical for cases in which we found etiologic noncoding, structural, and mitochondrial genome variants and coding variants poorly covered by exome sequencing. Cohortwide burden testing across 57,000 genomes enabled the discovery of three new disease genes and 19 new associations. Of the genetic diagnoses that we made, 25% had immediate ramifications for clinical decision making for the patients or their relatives.

Conclusions: Our pilot study of genome sequencing in a national health care system showed an increase in diagnostic yield across a range of rare diseases. (Funded by the National Institute for Health Research and others.).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1056/NEJMoa2035790DOI Listing
November 2021

Deficiency of TET3 leads to a genome-wide DNA hypermethylation episignature in human whole blood.

NPJ Genom Med 2021 Nov 8;6(1):92. Epub 2021 Nov 8.

Department of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA.

TET3 encodes an essential dioxygenase involved in epigenetic regulation through DNA demethylation. TET3 deficiency, or Beck-Fahrner syndrome (BEFAHRS; MIM: 618798), is a recently described neurodevelopmental disorder of the DNA demethylation machinery with a nonspecific phenotype resembling other chromatin-modifying disorders, but inconsistent variant types and inheritance patterns pose diagnostic challenges. Given TET3's direct role in regulating 5-methylcytosine and recent identification of syndrome-specific DNA methylation profiles, we analyzed genome-wide DNA methylation in whole blood of TET3-deficient individuals and identified an episignature that distinguishes affected and unaffected individuals and those with mono-allelic and bi-allelic pathogenic variants. Validation and testing of the episignature correctly categorized known TET3 variants and determined pathogenicity of variants of uncertain significance. Clinical utility was demonstrated when the episignature alone identified an affected individual from over 1000 undiagnosed cases and was confirmed upon distinguishing TET3-deficient individuals from those with 46 other disorders. The TET3-deficient signature - and the signature resulting from activating mutations in DNMT1 which normally opposes TET3 - are characterized by hypermethylation, which for BEFAHRS involves CpG sites that may be biologically relevant. This work expands the role of epi-phenotyping in molecular diagnosis and reveals genome-wide DNA methylation profiling as a quantitative, functional readout for characterization of this new biochemical category of disease.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41525-021-00256-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8576018PMC
November 2021

Biallelic TMEM260 variants cause truncus arteriosus, with or without renal defects.

Clin Genet 2021 Oct 6. Epub 2021 Oct 6.

Department of Pediatric Cardiology, Hadassah Medical Organization and Faculty of Medicine, Hebrew University of Jerusalem, Jerusalem, Israel.

Only two families have been reported with biallelic TMEM260 variants segregating with structural heart defects and renal anomalies syndrome (SHDRA). With a combination of genome, exome sequencing and RNA studies, we identified eight individuals from five families with biallelic TMEM260 variants. Variants included one multi-exon deletion, four nonsense/frameshifts, two splicing changes and one missense change. Together with the published cases, analysis of clinical data revealed ventricular septal defects (12/12), mostly secondary to truncus arteriosus (10/12), elevated creatinine levels (6/12), horse-shoe kidneys (1/12) and renal cysts (1/12) in patients. Three pregnancies were terminated on detection of severe congenital anomalies. Six patients died between the ages of 6 weeks and 5 years. Using a range of stringencies, carrier frequency for SHDRA was estimated at 0.0007-0.007 across ancestries. In conclusion, this study confirms the genetic basis of SHDRA, expands its known mutational spectrum and clarifies its clinical features. We demonstrate that SHDRA is a severe condition associated with substantial mortality in early childhood and characterised by congenital cardiac malformations with a variable renal phenotype.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/cge.14071DOI Listing
October 2021

A homozygous GRIN1 null variant causes a more severe phenotype of early infantile epileptic encephalopathy.

Am J Med Genet A 2021 Oct 6. Epub 2021 Oct 6.

Department of Paediatrics, Lancashire Teaching Hospitals NHS Foundation Trust, Lancashire, UK.

Pathogenic variants in glutamate receptor, ionotropic, NMDA-1 (GRIN1) cause an autosomal dominant or recessive neurodevelopmental disorder with global developmental delay, with or without seizures (AD or AR GRIN1-NDD). Here, we describe a novel homozygous canonical splice site variant in GRIN1 in a 12-month-old boy with early infantile epileptic encephalopathy and severe global developmental delay. This represents only the second family with a homozygous predicted-null variant in GRIN1 reported to date. We review the published literature on AR GRIN1-NDD and find that the phenotype in our patient is much more severe than those seen with homozygous missense variants. A similarly severe phenotype of intractable epilepsy and infantile death has only been reported in one other family with a homozygous nonsense variant in GRIN1. We, therefore, propose that biallelic predicted-null variants in GRIN1 can cause a markedly more severe clinical phenotype than AR GRIN1-NDD caused by missense variants.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/ajmg.a.62528DOI Listing
October 2021

Delineating the molecular and phenotypic spectrum of the SETD1B-related syndrome.

Genet Med 2021 11 3;23(11):2122-2137. Epub 2021 Aug 3.

Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, London, UK.

Purpose: Pathogenic variants in SETD1B have been associated with a syndromic neurodevelopmental disorder including intellectual disability, language delay, and seizures. To date, clinical features have been described for 11 patients with (likely) pathogenic SETD1B sequence variants. This study aims to further delineate the spectrum of the SETD1B-related syndrome based on characterizing an expanded patient cohort.

Methods: We perform an in-depth clinical characterization of a cohort of 36 unpublished individuals with SETD1B sequence variants, describing their molecular and phenotypic spectrum. Selected variants were functionally tested using in vitro and genome-wide methylation assays.

Results: Our data present evidence for a loss-of-function mechanism of SETD1B variants, resulting in a core clinical phenotype of global developmental delay, language delay including regression, intellectual disability, autism and other behavioral issues, and variable epilepsy phenotypes. Developmental delay appeared to precede seizure onset, suggesting SETD1B dysfunction impacts physiological neurodevelopment even in the absence of epileptic activity. Males are significantly overrepresented and more severely affected, and we speculate that sex-linked traits could affect susceptibility to penetrance and the clinical spectrum of SETD1B variants.

Conclusion: Insights from this extensive cohort will facilitate the counseling regarding the molecular and phenotypic landscape of newly diagnosed patients with the SETD1B-related syndrome.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41436-021-01246-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8553606PMC
November 2021

Post-translational formation of hypusine in eIF5A: implications in human neurodevelopment.

Amino Acids 2021 Jul 17. Epub 2021 Jul 17.

Columbia University, New York, NY, USA.

Hypusine [N-(4-amino-2-hydroxybutyl)lysine] is a derivative of lysine that is formed post-translationally in the eukaryotic initiation factor 5A (eIF5A). Its occurrence at a single site in one cellular protein defines hypusine synthesis as one of the most specific post-translational modifications. Synthesis of hypusine involves two enzymatic steps: first, deoxyhypusine synthase (DHPS) cleaves the 4-aminobutyl moiety of spermidine and transfers it to the ε-amino group of a specific lysine residue of the eIF5A precursor protein to form an intermediate, deoxyhypusine [N-(4-aminobutyl)lysine]. This intermediate is subsequently hydroxylated by deoxyhypusine hydroxylase (DOHH) to form hypusine in eIF5A. eIF5A, DHPS, and DOHH are highly conserved in all eukaryotes, and both enzymes exhibit a strict specificity toward eIF5A substrates. eIF5A promotes translation elongation globally by alleviating ribosome stalling and it also facilitates translation termination. Hypusine is required for the activity of eIF5A, mammalian cell proliferation, and animal development. Homozygous knockout of any of the three genes, Eif5a, Dhps, or Dohh, leads to embryonic lethality in mice. eIF5A has been implicated in various human pathological conditions. A recent genetic study reveals that heterozygous germline EIF5A variants cause Faundes-Banka syndrome, a craniofacial-neurodevelopmental malformations in humans. Biallelic variants of DHPS were identified as the genetic basis underlying a rare inherited neurodevelopmental disorder. Furthermore, biallelic DOHH variants also appear to be associated with neurodevelopmental disorder. The clinical phenotypes of these patients include intellectual disability, developmental delay, seizures, microcephaly, growth impairment, and/or facial dysmorphisms. Taken together, these findings underscore the importance of eIF5A and the hypusine modification pathway in neurodevelopment in humans.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s00726-021-03023-6DOI Listing
July 2021

Biallelic variants in PCDHGC4 cause a novel neurodevelopmental syndrome with progressive microcephaly, seizures, and joint anomalies.

Genet Med 2021 11 9;23(11):2138-2149. Epub 2021 Jul 9.

Department of Bioinformatics & Biotechnology, Faculty of Basic and Applied Sciences, International Islamic University, Islamabad, Pakistan.

Purpose: We aimed to define a novel autosomal recessive neurodevelopmental disorder, characterize its clinical features, and identify the underlying genetic cause for this condition.

Methods: We performed a detailed clinical characterization of 19 individuals from nine unrelated, consanguineous families with a neurodevelopmental disorder. We used genome/exome sequencing approaches, linkage and cosegregation analyses to identify disease-causing variants, and we performed three-dimensional molecular in silico analysis to predict causality of variants where applicable.

Results: In all affected individuals who presented with a neurodevelopmental syndrome with progressive microcephaly, seizures, and intellectual disability we identified biallelic disease-causing variants in Protocadherin-gamma-C4 (PCDHGC4). Five variants were predicted to induce premature protein truncation leading to a loss of PCDHGC4 function. The three detected missense variants were located in extracellular cadherin (EC) domains EC5 and EC6 of PCDHGC4, and in silico analysis of the affected residues showed that two of these substitutions were predicted to influence the Ca-binding affinity, which is essential for multimerization of the protein, whereas the third missense variant directly influenced the cis-dimerization interface of PCDHGC4.

Conclusion: We show that biallelic variants in PCDHGC4 are causing a novel autosomal recessive neurodevelopmental disorder and link PCDHGC4 as a member of the clustered PCDH family to a Mendelian disorder in humans.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41436-021-01260-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8553613PMC
November 2021

The diagnostic utility of clinical exome sequencing in 60 patients with hearing loss disorders: A single-institution experience.

Clin Otolaryngol 2021 11 5;46(6):1257-1262. Epub 2021 Jul 5.

Division of Evolution and Genomic Sciences, Manchester Academic Health Science Centre, Faculty of Biology, Medicine and Health, School of Biological Sciences, University of Manchester, Manchester, UK.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/coa.13826DOI Listing
November 2021

Haploinsufficiency of ARFGEF1 is associated with developmental delay, intellectual disability, and epilepsy with variable expressivity.

Genet Med 2021 10 10;23(10):1901-1911. Epub 2021 Jun 10.

Inserm UMR1231 team GAD, University of Burgundy and Franche-Comté, Dijon, France.

Purpose: ADP ribosylation factor guanine nucleotide exchange factors (ARFGEFs) are a family of proteins implicated in cellular trafficking between the Golgi apparatus and the plasma membrane through vesicle formation. Among them is ARFGEF1/BIG1, a protein involved in axon elongation, neurite development, and polarization processes. ARFGEF1 has been previously suggested as a candidate gene for different types of epilepsies, although its implication in human disease has not been well characterized.

Methods: International data sharing, in silico predictions, and in vitro assays with minigene study, western blot analyses, and RNA sequencing.

Results: We identified 13 individuals with heterozygous likely pathogenic variants in ARFGEF1. These individuals displayed congruent clinical features of developmental delay, behavioral problems, abnormal findings on brain magnetic resonance image (MRI), and epilepsy for almost half of them. While nearly half of the cohort carried de novo variants, at least 40% of variants were inherited from mildly affected parents who were clinically re-evaluated by reverse phenotyping. Our in silico predictions and in vitro assays support the contention that ARFGEF1-related conditions are caused by haploinsufficiency, and are transmitted in an autosomal dominant fashion with variable expressivity.

Conclusion: We provide evidence that loss-of-function variants in ARFGEF1 are implicated in sporadic and familial cases of developmental delay with or without epilepsy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41436-021-01218-6DOI Listing
October 2021

Recurrent KCNT2 missense variants affecting p.Arg190 result in a recognizable phenotype.

Am J Med Genet A 2021 10 1;185(10):3083-3091. Epub 2021 Jun 1.

Manchester Centre for Genomic Medicine, Division of Evolution and Genomic Sciences, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK.

KCNT2 variants resulting in substitutions affecting the Arg190 residue have been shown to cause epileptic encephalopathy and a recognizable facial gestalt. We report two additional individuals with intellectual disability, dysmorphic features, hypertrichosis, macrocephaly and the same de novo KCNT2 missense variants affecting the Arg190 residue as previously described. Notably, neither patient has epilepsy. Homology modeling of these missense variants revealed that they are likely to disrupt the stabilization of a closed channel conformation of KCNT2 resulting in a constitutively open state. This is the first report of pathogenic variants in KCNT2 causing a developmental phenotype without epilepsy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/ajmg.a.62370DOI Listing
October 2021

Non-coding region variants upstream of MEF2C cause severe developmental disorder through three distinct loss-of-function mechanisms.

Am J Hum Genet 2021 06 21;108(6):1083-1094. Epub 2021 May 21.

Human Genetics Programme, Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton CB10 1RQ, UK; East Anglian Medical Genetics Service, Cambridge University Hospitals NHS Foundation Trust, Cambridge CB2 0QQ, UK.

Clinical genetic testing of protein-coding regions identifies a likely causative variant in only around half of developmental disorder (DD) cases. The contribution of regulatory variation in non-coding regions to rare disease, including DD, remains very poorly understood. We screened 9,858 probands from the Deciphering Developmental Disorders (DDD) study for de novo mutations in the 5' untranslated regions (5' UTRs) of genes within which variants have previously been shown to cause DD through a dominant haploinsufficient mechanism. We identified four single-nucleotide variants and two copy-number variants upstream of MEF2C in a total of ten individual probands. We developed multiple bespoke and orthogonal experimental approaches to demonstrate that these variants cause DD through three distinct loss-of-function mechanisms, disrupting transcription, translation, and/or protein function. These non-coding region variants represent 23% of likely diagnoses identified in MEF2C in the DDD cohort, but these would all be missed in standard clinical genetics approaches. Nonetheless, these variants are readily detectable in exome sequence data, with 30.7% of 5' UTR bases across all genes well covered in the DDD dataset. Our analyses show that non-coding variants upstream of genes within which coding variants are known to cause DD are an important cause of severe disease and demonstrate that analyzing 5' UTRs can increase diagnostic yield. We also show how non-coding variants can help inform both the disease-causing mechanism underlying protein-coding variants and dosage tolerance of the gene.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.ajhg.2021.04.025DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8206381PMC
June 2021

Bi-allelic loss-of-function variants in BCAS3 cause a syndromic neurodevelopmental disorder.

Am J Hum Genet 2021 06 21;108(6):1069-1082. Epub 2021 May 21.

Manchester Centre for Genomic Medicine, St Mary's Hospital, Manchester University NHS Foundation Trust, Health Innovation Manchester, Manchester M13 9WL, UK.

BCAS3 microtubule-associated cell migration factor (BCAS3) is a large, highly conserved cytoskeletal protein previously proposed to be critical in angiogenesis and implicated in human embryogenesis and tumorigenesis. Here, we established BCAS3 loss-of-function variants as causative for a neurodevelopmental disorder. We report 15 individuals from eight unrelated families with germline bi-allelic loss-of-function variants in BCAS3. All probands share a global developmental delay accompanied by pyramidal tract involvement, microcephaly, short stature, strabismus, dysmorphic facial features, and seizures. The human phenotype is less severe compared with the Bcas3 knockout mouse model and cannot be explained by angiogenic defects alone. Consistent with being loss-of-function alleles, we observed absence of BCAS3 in probands' primary fibroblasts. By comparing the transcriptomic and proteomic data based on probands' fibroblasts with those of the knockout mouse model, we identified similar dysregulated pathways resulting from over-representation analysis, while the dysregulation of some proposed key interactors could not be confirmed. Together with the results from a tissue-specific Drosophila loss-of-function model, we demonstrate a vital role for BCAS3 in neural tissue development.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.ajhg.2021.04.024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8206390PMC
June 2021

Genotype-phenotype correlations and novel molecular insights into the DHX30-associated neurodevelopmental disorders.

Genome Med 2021 05 21;13(1):90. Epub 2021 May 21.

Département de Génétique, Hôpital La Pitié-Salpêtrière, Assistance Publique-Hôpitaux de Paris, Paris, France.

Background: We aimed to define the clinical and variant spectrum and to provide novel molecular insights into the DHX30-associated neurodevelopmental disorder.

Methods: Clinical and genetic data from affected individuals were collected through Facebook-based family support group, GeneMatcher, and our network of collaborators. We investigated the impact of novel missense variants with respect to ATPase and helicase activity, stress granule (SG) formation, global translation, and their effect on embryonic development in zebrafish. SG formation was additionally analyzed in CRISPR/Cas9-mediated DHX30-deficient HEK293T and zebrafish models, along with in vivo behavioral assays.

Results: We identified 25 previously unreported individuals, ten of whom carry novel variants, two of which are recurrent, and provide evidence of gonadal mosaicism in one family. All 19 individuals harboring heterozygous missense variants within helicase core motifs (HCMs) have global developmental delay, intellectual disability, severe speech impairment, and gait abnormalities. These variants impair the ATPase and helicase activity of DHX30, trigger SG formation, interfere with global translation, and cause developmental defects in a zebrafish model. Notably, 4 individuals harboring heterozygous variants resulting either in haploinsufficiency or truncated proteins presented with a milder clinical course, similar to an individual harboring a de novo mosaic HCM missense variant. Functionally, we established DHX30 as an ATP-dependent RNA helicase and as an evolutionary conserved factor in SG assembly. Based on the clinical course, the variant location, and type we establish two distinct clinical subtypes. DHX30 loss-of-function variants cause a milder phenotype whereas a severe phenotype is caused by HCM missense variants that, in addition to the loss of ATPase and helicase activity, lead to a detrimental gain-of-function with respect to SG formation. Behavioral characterization of dhx30-deficient zebrafish revealed altered sleep-wake activity and social interaction, partially resembling the human phenotype.

Conclusions: Our study highlights the usefulness of social media to define novel Mendelian disorders and exemplifies how functional analyses accompanied by clinical and genetic findings can define clinically distinct subtypes for ultra-rare disorders. Such approaches require close interdisciplinary collaboration between families/legal representatives of the affected individuals, clinicians, molecular genetics diagnostic laboratories, and research laboratories.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/s13073-021-00900-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8140440PMC
May 2021

Personalised virtual gene panels reduce interpretation workload and maintain diagnostic rates of proband-only clinical exome sequencing for rare disorders.

J Med Genet 2021 Apr 20. Epub 2021 Apr 20.

North West Genomic Laboratory Hub, Manchester Centre for Genomic Medicine, Manchester University NHS Foundation Trust, Manchester, Greater Manchester, UK.

Purpose: The increased adoption of genomic strategies in the clinic makes it imperative for diagnostic laboratories to improve the efficiency of variant interpretation. Clinical exome sequencing (CES) is becoming a valuable diagnostic tool, capable of meeting the diagnostic demand imposed by the vast array of different rare monogenic disorders. We have assessed a clinician-led and phenotype-based approach for virtual gene panel generation for analysis of targeted CES in patients with rare disease in a single institution.

Methods: Retrospective survey of 400 consecutive cases presumed by clinicians to have rare monogenic disorders, referred on singleton basis for targeted CES. We evaluated diagnostic yield and variant workload to characterise the usefulness of a clinician-led approach for generation of virtual gene panels that can incorporate up to three different phenotype-driven gene selection methods.

Results: Abnormalities of the nervous system (54.5%), including intellectual disability, head and neck (19%), skeletal system (16%), ear (15%) and eye (15%) were the most common clinical features reported in referrals. Combined phenotype-driven strategies for virtual gene panel generation were used in 57% of cases. On average, 7.3 variants (median=5) per case were retained for clinical interpretation. The overall diagnostic rate of proband-only CES using personalised phenotype-driven virtual gene panels was 24%.

Conclusions: Our results show that personalised virtual gene panels are a cost-effective approach for variant analysis of CES, maintaining diagnostic yield and optimising the use of resources for clinical genomic sequencing in the clinic.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1136/jmedgenet-2020-107303DOI Listing
April 2021

Clinical delineation, sex differences, and genotype-phenotype correlation in pathogenic KDM6A variants causing X-linked Kabuki syndrome type 2.

Genet Med 2021 07 5;23(7):1202-1210. Epub 2021 Mar 5.

Genetic Health Queensland c/-Royal Brisbane and Women's Hospital, Herston, QLD, Australia.

Purpose: The variant spectrum and the phenotype of X-linked Kabuki syndrome type 2 (KS2) are poorly understood.

Methods: Genetic and clinical details of new and published individuals with pathogenic KDM6A variants were compiled and analyzed.

Results: Sixty-one distinct pathogenic KDM6A variants (50 truncating, 11 missense) from 80 patients (34 males, 46 females) were identified. Missense variants clustered in the TRP 2, 3, 7 and Jmj-C domains. Truncating variants were significantly more likely to be de novo. Thirteen individuals had maternally inherited variants and one had a paternally inherited variant. Neonatal feeding difficulties, hypoglycemia, postnatal growth retardation, poor weight gain, motor delay, intellectual disability (ID), microcephaly, congenital heart anomalies, palate defects, renal malformations, strabismus, hearing loss, recurrent infections, hyperinsulinism, seizures, joint hypermobility, and gastroesophageal reflux were frequent clinical findings. Facial features of over a third of patients were not typical for KS. Males were significantly more likely to be born prematurely, have shorter stature, and severe developmental delay/ID.

Conclusion: We expand the KDM6A variant spectrum and delineate the KS2 phenotype. We demonstrate that the variability of the KS2 phenotypic depends on sex and the variant type. We also highlight the overlaps and differences between the phenotypes of KS2 and KS1.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41436-021-01119-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8257478PMC
July 2021

ERBB4 exonic deletions on chromosome 2q34 in patients with intellectual disability or epilepsy.

Eur J Hum Genet 2021 Sep 18;29(9):1377-1383. Epub 2021 Feb 18.

Manchester Centre for Genomic Medicine, St Mary's Hospital, Manchester University NHS Foundation Trust, Manchester, UK.

ERBB4 encodes the tyrosine kinase receptor HER4, a critical regulator of normal cell function and neurodevelopmental processes in the brain. One of the key ligands of HER4 is neureglin-1 (NRG1), and the HER4-NRG1 signalling pathway is essential in neural crest cell migration, and neuronal differentiation. Pharmacological inactivation of HER4 has been shown to hasten the progression of epileptogenesis in rodent models, and heterozygous ERBB4 null mice are shown to have cognitive deficits and delayed motor development. Thus far there is only a single case report in the literature of a heterozygous ERBB4 deletion in a patient with intellectual disability (ID). We identified nine subjects from five unrelated families with chromosome 2q34 deletions, resulting in heterozygous intragenic loss of multiple exons of ERBB4, associated with either non-syndromic ID or generalised epilepsy. In one family, the deletion segregated with ID in five affected relatives. Overall, this case series further supports that haploinsufficiency of ERBB4 leads to non-syndromic intellectual disability or epilepsy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41431-021-00815-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8440581PMC
September 2021

SPEN haploinsufficiency causes a neurodevelopmental disorder overlapping proximal 1p36 deletion syndrome with an episignature of X chromosomes in females.

Am J Hum Genet 2021 03 16;108(3):502-516. Epub 2021 Feb 16.

Division of Medical Genetics, Department of Pediatrics, UPMC Children's Hospital of Pittsburgh, Pittsburgh, PA 15224, USA.

Deletion 1p36 (del1p36) syndrome is the most common human disorder resulting from a terminal autosomal deletion. This condition is molecularly and clinically heterogeneous. Deletions involving two non-overlapping regions, known as the distal (telomeric) and proximal (centromeric) critical regions, are sufficient to cause the majority of the recurrent clinical features, although with different facial features and dysmorphisms. SPEN encodes a transcriptional repressor commonly deleted in proximal del1p36 syndrome and is located centromeric to the proximal 1p36 critical region. Here, we used clinical data from 34 individuals with truncating variants in SPEN to define a neurodevelopmental disorder presenting with features that overlap considerably with those of proximal del1p36 syndrome. The clinical profile of this disease includes developmental delay/intellectual disability, autism spectrum disorder, anxiety, aggressive behavior, attention deficit disorder, hypotonia, brain and spine anomalies, congenital heart defects, high/narrow palate, facial dysmorphisms, and obesity/increased BMI, especially in females. SPEN also emerges as a relevant gene for del1p36 syndrome by co-expression analyses. Finally, we show that haploinsufficiency of SPEN is associated with a distinctive DNA methylation episignature of the X chromosome in affected females, providing further evidence of a specific contribution of the protein to the epigenetic control of this chromosome, and a paradigm of an X chromosome-specific episignature that classifies syndromic traits. We conclude that SPEN is required for multiple developmental processes and SPEN haploinsufficiency is a major contributor to a disorder associated with deletions centromeric to the previously established 1p36 critical regions.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.ajhg.2021.01.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8008487PMC
March 2021

Impaired eIF5A function causes a Mendelian disorder that is partially rescued in model systems by spermidine.

Nat Commun 2021 02 5;12(1):833. Epub 2021 Feb 5.

Division of Evolution & Genomic Sciences, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK.

The structure of proline prevents it from adopting an optimal position for rapid protein synthesis. Poly-proline-tract (PPT) associated ribosomal stalling is resolved by highly conserved eIF5A, the only protein to contain the amino acid hypusine. We show that de novo heterozygous EIF5A variants cause a disorder characterized by variable combinations of developmental delay, microcephaly, micrognathia and dysmorphism. Yeast growth assays, polysome profiling, total/hypusinated eIF5A levels and PPT-reporters studies reveal that the variants impair eIF5A function, reduce eIF5A-ribosome interactions and impair the synthesis of PPT-containing proteins. Supplementation with 1 mM spermidine partially corrects the yeast growth defects, improves the polysome profiles and restores expression of PPT reporters. In zebrafish, knockdown eif5a partly recapitulates the human phenotype that can be rescued with 1 µM spermidine supplementation. In summary, we uncover the role of eIF5A in human development and disease, demonstrate the mechanistic complexity of EIF5A-related disorder and raise possibilities for its treatment.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-021-21053-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7864902PMC
February 2021

Mutation-specific pathophysiological mechanisms define different neurodevelopmental disorders associated with SATB1 dysfunction.

Am J Hum Genet 2021 02 28;108(2):346-356. Epub 2021 Jan 28.

Department of Rehabilitation and Development, Randall Children's Hospital at Legacy Emanuel Medical Center, Portland, OR 97227, USA.

Whereas large-scale statistical analyses can robustly identify disease-gene relationships, they do not accurately capture genotype-phenotype correlations or disease mechanisms. We use multiple lines of independent evidence to show that different variant types in a single gene, SATB1, cause clinically overlapping but distinct neurodevelopmental disorders. Clinical evaluation of 42 individuals carrying SATB1 variants identified overt genotype-phenotype relationships, associated with different pathophysiological mechanisms, established by functional assays. Missense variants in the CUT1 and CUT2 DNA-binding domains result in stronger chromatin binding, increased transcriptional repression, and a severe phenotype. In contrast, variants predicted to result in haploinsufficiency are associated with a milder clinical presentation. A similarly mild phenotype is observed for individuals with premature protein truncating variants that escape nonsense-mediated decay, which are transcriptionally active but mislocalized in the cell. Our results suggest that in-depth mutation-specific genotype-phenotype studies are essential to capture full disease complexity and to explain phenotypic variability.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.ajhg.2021.01.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7895900PMC
February 2021

New insights into the clinical and molecular spectrum of the novel CYFIP2-related neurodevelopmental disorder and impairment of the WRC-mediated actin dynamics.

Genet Med 2021 03 5;23(3):543-554. Epub 2020 Nov 5.

Department of Medical Genetics, Lyon University Hospital, Lyon, France.

Purpose: A few de novo missense variants in the cytoplasmic FMRP-interacting protein 2 (CYFIP2) gene have recently been described as a novel cause of severe intellectual disability, seizures, and hypotonia in 18 individuals, with p.Arg87 substitutions in the majority.

Methods: We assembled data from 19 newly identified and all 18 previously published individuals with CYFIP2 variants. By structural modeling and investigation of WAVE-regulatory complex (WRC)-mediated actin polymerization in six patient fibroblast lines we assessed the impact of CYFIP2 variants on the WRC.

Results: Sixteen of 19 individuals harbor two previously described and 11 novel (likely) disease-associated missense variants. We report p.Asp724 as second mutational hotspot (4/19 cases). Genotype-phenotype correlation confirms a consistently severe phenotype in p.Arg87 patients but a more variable phenotype in p.Asp724 and other substitutions. Three individuals with milder phenotypes carry putative loss-of-function variants, which remain of unclear pathogenicity. Structural modeling predicted missense variants to disturb interactions within the WRC or impair CYFIP2 stability. Consistent with its role in WRC-mediated actin polymerization we substantiate aberrant regulation of the actin cytoskeleton in patient fibroblasts.

Conclusion: Our study expands the clinical and molecular spectrum of CYFIP2-related neurodevelopmental disorder and provides evidence for aberrant WRC-mediated actin dynamics as contributing cellular pathomechanism.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41436-020-01011-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7935717PMC
March 2021

Haploinsufficiency of ATP6V0C possibly underlies 16p13.3 deletions that cause microcephaly, seizures, and neurodevelopmental disorder.

Am J Med Genet A 2020 Oct 8. Epub 2020 Oct 8.

Manchester Centre for Genomic Medicine, St. Mary's Hospital, Manchester University Foundation NHS Trust, Manchester, UK.

We recently contributed to the description of eight individuals with a novel condition caused by 16p13.3 microdeletions encompassing TBC1D24, ATP6V0C, and PDPK1 and resulting in epilepsy, microcephaly and neurodevelopmental problems. The phenotypic spectrum, the minimum overlapping region and the underlying disease mechanism for this disorder remain to be clarified. Here we report a 3.5-year-old male, with microcephaly, autism spectrum disorder and a de novo 16p13.3 microdeletion. We performed detailed in silico analysis to show that the minimum overlapping region for the condition is ~80Kb encompassing five protein coding genes. Analysis of loss of function constraint metrics, transcript-aware evaluation of the population variants, GeVIR scores, analysis of reported pathogenic point variants, detailed review of the known functions of gene products and their animal models showed that the haploinsufficiency of ATP6V0C likely underlies the phenotype of this condition. Protein-protein interaction network, gene phenology and analysis of topologically associating domain showed that it was unlikely that the disorder has an epistatic or regulatory basis. 16p13.3 deletions encompassing ATP6V0C cause a neurodevelopmental disorder. Our results broaden the phenotypic spectrum of this disorder and clarify the likely underlying disease mechanism for the condition.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/ajmg.a.61905DOI Listing
October 2020

Neutrophil dysfunction triggers inflammatory bowel disease in G6PC3 deficiency.

J Leukoc Biol 2021 06 15;109(6):1147-1154. Epub 2020 Sep 15.

Lydia Becker Institute of Immunology and Inflammation, University of Manchester, Manchester, UK.

The glucose-6-phosphatase catalytic subunit 3 (G6PC3) encodes a ubiquitously expressed enzyme that regulates cytoplasmic glucose availability. Loss-of-function biallelic G6PC3 mutations cause severe congenital neutropenia and a diverse spectrum of extra-hematological manifestations, among which inflammatory bowel disease (IBD) has been anecdotally reported. Neutrophil function and clinical response to granulocyte colony-stimulating factor (G-CSF) and hematopoietic stem cell transplantation (HSCT) were investigated in 4 children with G6PC3 deficiency-associated IBD. G6PC3 deficiency was associated with early-onset IBD refractory to treatment with steroids and infliximab. The symptoms of IBD progressed despite G-CSF treatment. In vitro studies on the patients' blood showed that neutrophils displayed higher levels of activation markers (CD11b, CD66b, and CD14), excessive IL-8 and reactive oxygen species, and increased apoptosis and secondary necrosis. Secondary necrosis was exaggerated after stimulation with Escherichia coli and could be partially rescued with supplemental exogenous glucose. HSCT led to normalization of neutrophil function and remission of gastrointestinal symptoms. We conclude that neutrophils in G6PC3 deficiency release pro-inflammatory mediators when exposed to gut bacteria, associated with intestinal inflammation, despite treatment with G-CSF. HSCT is an effective therapeutic option in patients with G6PC3 deficiency-associated IBD refractory to immune suppressants.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/JLB.5AB1219-699RRDOI Listing
June 2021

Reply: Expanding the clinical and genetic spectrum of PCYT2-related disorders.

Brain 2020 09;143(9):e77

Manchester Centre for Genomics Medicine, St Mary's Hospital, Manchester University Hospital Foundation Trust, Health Innovation Manchester, Manchester, M13 9WL, UK.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/brain/awaa230DOI Listing
September 2020

Telemedicine strategy of the European Reference Network ITHACA for the diagnosis and management of patients with rare developmental disorders.

Orphanet J Rare Dis 2020 04 25;15(1):103. Epub 2020 Apr 25.

Manchester Centre for Genomic Medicine, St Mary's Hospital, Manchester University Hospitals NHS Foundation Trust, Manchester Academic Health Sciences Centre, Manchester, M13 9WL, UK.

Background: The European Reference Networks, ERNs, are virtual networks for healthcare providers across Europe to collaborate and share expertise on complex or rare diseases and conditions. As part of the ERNs, the Clinical Patient Management System, CPMS, a secure digital platform, was developed to allow and facilitate web-based, clinical consultations between submitting clinicians and relevant international experts. The European Reference Network on Intellectual Disability, TeleHealth and Congenital Anomalies, ERN ITHACA, was formed to harness the clinical and diagnostic expertise in the sector of rare, multiple anomaly and/or intellectual disability syndromes, chromosome disorders and undiagnosed syndromic disorders. We present the first year results of CPMS use by ERN ITHACA as an example of a telemedicine strategy for the diagnosis and management of patients with rare developmental disorders.

Results: ERN ITHACA ranked third in telemedicine activity amongst 24 European networks after 12 months of using the CPMS. Information about 28 very rare cases from 13 different centres across 7 countries was shared on the platform, with diagnostic or other management queries. Early interaction with patient support groups identified data protection as of primary importance in adopting digital platforms for patient diagnosis and care. The first launch of the CPMS was built to accommodate the needs of all ERNs. The ERN ITHACA telemedicine process highlighted a need to customise the CPMS with network-specific requirements. The results of this effort should enhance the CPMS utility for telemedicine services and ERN-specific care outcomes.

Conclusions: We present the results of a long and fruitful process of interaction between the ERN ITHACA network lead team and EU officials, software developers and members of 38 EU clinical genetics centres to organise and coordinate direct e-healthcare through a secure, digital platform. The variability of the queries in just the first 28 cases submitted to the ERN ITHACA CPMS is a fair representation of the complexity and rarity of the patients referred, but also proof of the sophisticated and variable service that could be provided through a structured telemedicine approach for patients and families with rare developmental disorders. Web-based approaches are likely to result in increased accessibility to clinical genomic services.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/s13023-020-1349-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7183125PMC
April 2020

Expanding Clinical Presentations Due to Variations in THOC2 mRNA Nuclear Export Factor.

Front Mol Neurosci 2020 11;13:12. Epub 2020 Feb 11.

Adelaide Medical School and the Robinson Research Institute, The University of Adelaide, Adelaide, SA, Australia.

Multiple TREX mRNA export complex subunits (e.g., THOC1, THOC2, THOC5, THOC6, THOC7) have now been implicated in neurodevelopmental disorders (NDDs), neurodegeneration and cancer. We previously implicated missense and splicing-defective variants in NDDs and a broad range of other clinical features. Here we report 10 individuals from nine families with rare missense variants including the first case of a recurrent variant (p.Arg77Cys), and an additional individual with an intragenic microdeletion (Del-Ex37-38). missense variant testing and patient-derived cell line data from current and published studies show 9 of the 14 missense THOC2 variants result in reduced protein stability. The splicing-defective and deletion variants result in a loss of small regions of the C-terminal THOC2 RNA binding domain (RBD). Interestingly, reduced stability of THOC2 variant proteins has a flow-on effect on the stability of the multi-protein TREX complex; specifically on the other NDD-associated THOC subunits. Our current, expanded cohort refines the core phenotype of THOC2 NDDs to language disorder and/or ID, with a variable severity, and disorders of growth. A subset of affected individuals' has severe-profound ID, persistent hypotonia and respiratory abnormalities. Further investigations to elucidate the pathophysiological basis for this severe phenotype are warranted.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fnmol.2020.00012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7026477PMC
February 2020

Opposite Modulation of RAC1 by Mutations in TRIO Is Associated with Distinct, Domain-Specific Neurodevelopmental Disorders.

Am J Hum Genet 2020 03 27;106(3):338-355. Epub 2020 Feb 27.

Developmental Brain Disorders Laboratory, INSERM UMR 1163, 75015 Paris, France; Service de Génétique, Necker Enfants Malades University Hospital, Assistance Publique-Hôpitaux de Pairs, 75015 Paris, France.

The Rho-guanine nucleotide exchange factor (RhoGEF) TRIO acts as a key regulator of neuronal migration, axonal outgrowth, axon guidance, and synaptogenesis by activating the GTPase RAC1 and modulating actin cytoskeleton remodeling. Pathogenic variants in TRIO are associated with neurodevelopmental diseases, including intellectual disability (ID) and autism spectrum disorders (ASD). Here, we report the largest international cohort of 24 individuals with confirmed pathogenic missense or nonsense variants in TRIO. The nonsense mutations are spread along the TRIO sequence, and affected individuals show variable neurodevelopmental phenotypes. In contrast, missense variants cluster into two mutational hotspots in the TRIO sequence, one in the seventh spectrin repeat and one in the RAC1-activating GEFD1. Although all individuals in this cohort present with developmental delay and a neuro-behavioral phenotype, individuals with a pathogenic variant in the seventh spectrin repeat have a more severe ID associated with macrocephaly than do most individuals with GEFD1 variants, who display milder ID and microcephaly. Functional studies show that the spectrin and GEFD1 variants cause a TRIO-mediated hyper- or hypo-activation of RAC1, respectively, and we observe a striking correlation between RAC1 activation levels and the head size of the affected individuals. In addition, truncations in TRIO GEFD1 in the vertebrate model X. tropicalis induce defects that are concordant with the human phenotype. This work demonstrates distinct clinical and molecular disorders clustering in the GEFD1 and seventh spectrin repeat domains and highlights the importance of tight control of TRIO-RAC1 signaling in neuronal development.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.ajhg.2020.01.018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7058823PMC
March 2020

A restricted spectrum of missense KMT2D variants cause a multiple malformations disorder distinct from Kabuki syndrome.

Genet Med 2020 05 17;22(5):867-877. Epub 2020 Jan 17.

Division of Cell Matrix Biology and Regenerative Medicine, School of Biological Sciences, Faculty of Biology, Medicine, and Health, The University of Manchester, Manchester, UK.

Purpose: To investigate if specific exon 38 or 39 KMT2D missense variants (MVs) cause a condition distinct from Kabuki syndrome type 1 (KS1).

Methods: Multiple individuals, with MVs in exons 38 or 39 of KMT2D that encode a highly conserved region of 54 amino acids flanked by Val3527 and Lys3583, were identified and phenotyped. Functional tests were performed to study their pathogenicity and understand the disease mechanism.

Results: The consistent clinical features of the affected individuals, from seven unrelated families, included choanal atresia, athelia or hypoplastic nipples, branchial sinus abnormalities, neck pits, lacrimal duct anomalies, hearing loss, external ear malformations, and thyroid abnormalities. None of the individuals had intellectual disability. The frequency of clinical features, objective software-based facial analysis metrics, and genome-wide peripheral blood DNA methylation patterns in these patients were significantly different from that of KS1. Circular dichroism spectroscopy indicated that these MVs perturb KMT2D secondary structure through an increased disordered to ɑ-helical transition.

Conclusion: KMT2D MVs located in a specific region spanning exons 38 and 39 and affecting highly conserved residues cause a novel multiple malformations syndrome distinct from KS1. Unlike KMT2D haploinsufficiency in KS1, these MVs likely result in disease through a dominant negative mechanism.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41436-019-0743-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7200597PMC
May 2020

Delineation of a Human Mendelian Disorder of the DNA Demethylation Machinery: TET3 Deficiency.

Am J Hum Genet 2020 02 9;106(2):234-245. Epub 2020 Jan 9.

Division of Evolution & Genomic Sciences, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester M13 9PL, UK; Manchester Centre for Genomic Medicine, St Mary's Hospital, Manchester University NHS Foundation Trust, Health Innovation Manchester, Manchester M13 9WL, UK.

Germline pathogenic variants in chromatin-modifying enzymes are a common cause of pediatric developmental disorders. These enzymes catalyze reactions that regulate epigenetic inheritance via histone post-translational modifications and DNA methylation. Cytosine methylation (5-methylcytosine [5mC]) of DNA is the quintessential epigenetic mark, yet no human Mendelian disorder of DNA demethylation has yet been delineated. Here, we describe in detail a Mendelian disorder caused by the disruption of DNA demethylation. TET3 is a methylcytosine dioxygenase that initiates DNA demethylation during early zygote formation, embryogenesis, and neuronal differentiation and is intolerant to haploinsufficiency in mice and humans. We identify and characterize 11 cases of human TET3 deficiency in eight families with the common phenotypic features of intellectual disability and/or global developmental delay; hypotonia; autistic traits; movement disorders; growth abnormalities; and facial dysmorphism. Mono-allelic frameshift and nonsense variants in TET3 occur throughout the coding region. Mono-allelic and bi-allelic missense variants localize to conserved residues; all but one such variant occur within the catalytic domain, and most display hypomorphic function in an assay of catalytic activity. TET3 deficiency and other Mendelian disorders of the epigenetic machinery show substantial phenotypic overlap, including features of intellectual disability and abnormal growth, underscoring shared disease mechanisms.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.ajhg.2019.12.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7010978PMC
February 2020
-->