Publications by authors named "Ganka Douglas"

39 Publications

Uniparental disomy in a population of 32,067 clinical exome trios.

Genet Med 2021 Jan 25. Epub 2021 Jan 25.

GeneDx, Gaithersburg, MD, USA.

Purpose: Data on the clinical prevalence and spectrum of uniparental disomy (UPD) remain limited. Trio exome sequencing (ES) presents a comprehensive method for detection of UPD alongside sequence and copy-number variant analysis.

Methods: We analyzed 32,067 ES trios referred for diagnostic testing to create a profile of UPD events and their disease associations. ES single-nucleotide polymorphism (SNP) and copy-number data were used to identify both whole-chromosome and segmental UPD and to categorize whole-chromosome results as isodisomy, heterodisomy, or mixed.

Results: Ninety-nine whole-chromosome and 13 segmental UPD events were identified. Of these, 29 were associated with an imprinting disorder, and 16 were associated with a positive test result through homozygous sequence variants. Isodisomy was more commonly observed in large chromosomes along with a higher rate of homozygous pathogenic variants, while heterodisomy was more frequent in chromosomes associated with imprinting or trisomy mosaicism (14, 15, 16, 20, 22).

Conclusion: Whole-chromosome UPD was observed in 0.31% of cases, resulting in a diagnostic finding in 0.14%. Only three UPD-positive cases had a diagnostic finding unrelated to the UPD. Thirteen UPD events were identified in cases with prior normal SNP chromosomal microarray results, demonstrating the additional diagnostic value of UPD detection by trio ES.
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http://dx.doi.org/10.1038/s41436-020-01092-8DOI Listing
January 2021

NEMF mutations that impair ribosome-associated quality control are associated with neuromuscular disease.

Nat Commun 2020 09 15;11(1):4625. Epub 2020 Sep 15.

The Jackson Laboratory, Bar Harbor, ME, USA.

A hallmark of neurodegeneration is defective protein quality control. The E3 ligase Listerin (LTN1/Ltn1) acts in a specialized protein quality control pathway-Ribosome-associated Quality Control (RQC)-by mediating proteolytic targeting of incomplete polypeptides produced by ribosome stalling, and Ltn1 mutation leads to neurodegeneration in mice. Whether neurodegeneration results from defective RQC and whether defective RQC contributes to human disease have remained unknown. Here we show that three independently-generated mouse models with mutations in a different component of the RQC complex, NEMF/Rqc2, develop progressive motor neuron degeneration. Equivalent mutations in yeast Rqc2 selectively interfere with its ability to modify aberrant translation products with C-terminal tails which assist with RQC-mediated protein degradation, suggesting a pathomechanism. Finally, we identify NEMF mutations expected to interfere with function in patients from seven families presenting juvenile neuromuscular disease. These uncover NEMF's role in translational homeostasis in the nervous system and implicate RQC dysfunction in causing neurodegeneration.
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http://dx.doi.org/10.1038/s41467-020-18327-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7494853PMC
September 2020

Biallelic variants in the RNA exosome gene EXOSC5 are associated with developmental delays, short stature, cerebellar hypoplasia and motor weakness.

Hum Mol Genet 2020 Aug;29(13):2218-2239

Department of Biology, Emory University, Atlanta, GA 30322, USA.

The RNA exosome is an essential ribonuclease complex required for processing and/or degradation of both coding and non-coding RNAs. We identified five patients with biallelic variants in EXOSC5, which encodes a structural subunit of the RNA exosome. The clinical features of these patients include failure to thrive, short stature, feeding difficulties, developmental delays that affect motor skills, hypotonia and esotropia. Brain MRI revealed cerebellar hypoplasia and ventriculomegaly. While we ascertained five patients, three patients with distinct variants of EXOSC5 were studied in detail. The first patient had a deletion involving exons 5-6 of EXOSC5 and a missense variant, p.Thr114Ile, that were inherited in trans, the second patient was homozygous for p.Leu206His and the third patient had paternal isodisomy for chromosome 19 and was homozygous for p.Met148Thr. The additional two patients ascertained are siblings who had an early frameshift mutation in EXOSC5 and the p.Thr114Ile missense variant that were inherited in trans. We employed three complementary approaches to explore the requirement for EXOSC5 in brain development and assess consequences of pathogenic EXOSC5 variants. Loss of function for exosc5 in zebrafish results in shortened and curved tails/bodies, reduced eye/head size and edema. We modeled pathogenic EXOSC5 variants in both budding yeast and mammalian cells. Some of these variants cause defects in RNA exosome function as well as altered interactions with other RNA exosome subunits. These findings expand the number of genes encoding RNA exosome subunits linked to human disease while also suggesting that disease mechanism varies depending on the specific pathogenic variant.
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http://dx.doi.org/10.1093/hmg/ddaa108DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7399534PMC
August 2020

De Novo Frameshift Variants in the Neuronal Splicing Factor NOVA2 Result in a Common C-Terminal Extension and Cause a Severe Form of Neurodevelopmental Disorder.

Am J Hum Genet 2020 04 19;106(4):438-452. Epub 2020 Mar 19.

Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch 67400, France; Centre National de la Recherche Scientifique, UMR7104, Illkirch 67400, France; Institut National de la Santé et de la Recherche Médicale, U964, Illkirch 67400, France; Université de Strasbourg, Illkirch 67400, France; Laboratory of Genetic Diagnostic, Hôpitaux Universitaires de Strasbourg, Strasbourg 67000, France. Electronic address:

The neuro-oncological ventral antigen 2 (NOVA2) protein is a major factor regulating neuron-specific alternative splicing (AS), previously associated with an acquired neurologic condition, the paraneoplastic opsoclonus-myoclonus ataxia (POMA). We report here six individuals with de novo frameshift variants in NOVA2 affected with a severe neurodevelopmental disorder characterized by intellectual disability (ID), motor and speech delay, autistic features, hypotonia, feeding difficulties, spasticity or ataxic gait, and abnormal brain MRI. The six variants lead to the same reading frame, adding a common proline rich C-terminal part instead of the last KH RNA binding domain. We detected 41 genes differentially spliced after NOVA2 downregulation in human neural cells. The NOVA2 variant protein shows decreased ability to bind target RNA sequences and to regulate target AS events. It also fails to complement the effect on neurite outgrowth induced by NOVA2 downregulation in vitro and to rescue alterations of retinotectal axonal pathfinding induced by loss of NOVA2 ortholog in zebrafish. Our results suggest a partial loss-of-function mechanism rather than a full heterozygous loss-of-function, although a specific contribution of the novel C-terminal extension cannot be excluded.
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http://dx.doi.org/10.1016/j.ajhg.2020.02.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7118572PMC
April 2020

Missense variants in TAF1 and developmental phenotypes: challenges of determining pathogenicity.

Hum Mutat 2019 Oct 23. Epub 2019 Oct 23.

Institute for Basic Research in Developmental Disabilities (IBR), Staten Island, NY, USA.

We recently described a new neurodevelopmental syndrome (TAF1/MRXS33 intellectual disability syndrome) (MIM# 300966) caused by pathogenic variants involving the X-linked gene TAF1, which participates in RNA polymerase II transcription. The initial study reported eleven families, and the syndrome was defined as presenting early in life with hypotonia, facial dysmorphia, and developmental delay that evolved into intellectual disability (ID) and/or autism spectrum disorder (ASD). We have now identified an additional 27 families through a genotype-first approach. Familial segregation analysis, clinical phenotyping, and bioinformatics were capitalized on to assess potential variant pathogenicity, and molecular modelling was performed for those variants falling within structurally characterized domains of TAF1. A novel phenotypic clustering approach was also applied, in which the phenotypes of affected individuals were classified using 51 standardized Human Phenotype Ontology (HPO) terms. Phenotypes associated with TAF1 variants show considerable pleiotropy and clinical variability, but prominent among previously unreported effects were brain morphological abnormalities, seizures, hearing loss, and heart malformations. Our allelic series broadens the phenotypic spectrum of TAF1/MRXS33 intellectual disability syndrome and the range of TAF1 molecular defects in humans. It also illustrates the challenges for determining the pathogenicity of inherited missense variants, particularly for genes mapping to chromosome X. This article is protected by copyright. All rights reserved.
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http://dx.doi.org/10.1002/humu.23936DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7187541PMC
October 2019

Confirmation that variants in TTI2 are responsible for autosomal recessive intellectual disability.

Clin Genet 2019 10 17;96(4):354-358. Epub 2019 Jul 17.

Département de Biochimie et Génétique du CHU d'Angers, Centre Hospitalier Universitaire d'Angers, Angers, France.

TTI2 (MIM 614126) has been described as responsible for autosomal recessive intellectual disability (ID; MRT39, MIM:615541) in only two inbred families. Here, we give an account of two individuals from two unrelated outbred families harbouring compound heterozygous TTI2 pathogenic variants. Together with severe ID, progressive microcephaly, scoliosis and sleeping disorder are the most striking features in the two individuals concerned. TTI2, together with TTI1 and TELO2, encode proteins that constitute the triple T heterotrimeric complex. This TTT complex interacts with the HSP90 and R2TP to form a super-complex that has a chaperone function stabilising and maturing a number of kinases, such as ataxia-telangiectasia mutated and mechanistic target of rapamycin, which are key regulators of cell proliferation and genome maintenance. Pathogenic variants in TTI2 logically result in a phenotype close to that caused by TELO2 variants.
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http://dx.doi.org/10.1111/cge.13603DOI Listing
October 2019

Author Correction: CHD3 helicase domain mutations cause a neurodevelopmental syndrome with macrocephaly and impaired speech and language.

Nat Commun 2019 May 2;10(1):2079. Epub 2019 May 2.

CHU Sainte-Justine Research Center, Montreal, QC H3T 1C5, Canada.

The HTML and PDF versions of this Article were updated after publication to remove images of one individual from Figure 1.
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http://dx.doi.org/10.1038/s41467-019-10161-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6497626PMC
May 2019

SON haploinsufficiency causes impaired pre-mRNA splicing of CAKUT genes and heterogeneous renal phenotypes.

Kidney Int 2019 06 15;95(6):1494-1504. Epub 2019 Mar 15.

Mitchell Cancer Institute, University of South Alabama, Mobile, Alabama, USA; Department of Biochemistry and Molecular Biology, College of Medicine, University of South Alabama, Mobile, Alabama, USA. Electronic address:

Although genetic testing is increasingly used in clinical nephrology, a large number of patients with congenital abnormalities of the kidney and urinary tract (CAKUT) remain undiagnosed with current gene panels. Therefore, careful curation of novel genetic findings is key to improving diagnostic yields. We recently described a novel intellectual disability syndrome caused by de novo heterozygous loss-of-function mutations in the gene encoding the splicing factor SON. Here, we show that many of these patients, including two previously unreported, exhibit a wide array of kidney abnormalities. Detailed phenotyping of 14 patients with SON haploinsufficiency identified kidney anomalies in 8 patients, including horseshoe kidney, unilateral renal hypoplasia, and renal cysts. Recurrent urinary tract infections, electrolyte disturbances, and hypertension were also observed in some patients. SON knockdown in kidney cell lines leads to abnormal pre-mRNA splicing, resulting in decreased expression of several established CAKUT genes. Furthermore, these molecular events were observed in patient-derived cells with SON haploinsufficiency. Taken together, our data suggest that the wide spectrum of phenotypes in patients with a pathogenic SON mutation is a consequence of impaired pre-mRNA splicing of several CAKUT genes. We propose that genetic testing panels designed to diagnose children with a kidney phenotype should include the SON gene.
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http://dx.doi.org/10.1016/j.kint.2019.01.025DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6534475PMC
June 2019

De novo variants in HK1 associated with neurodevelopmental abnormalities and visual impairment.

Eur J Hum Genet 2019 07 18;27(7):1081-1089. Epub 2019 Feb 18.

Department of Pediatrics, Columbia University Medical Center, New York, NY, USA.

Hexokinase 1 (HK1) phosphorylates glucose to glucose-6-phosphate, the first rate-limiting step in glycolysis. Homozygous and heterozygous variants in HK1 have been shown to cause autosomal recessive non-spherocytic hemolytic anemia, autosomal recessive Russe type hereditary motor and sensory neuropathy, and autosomal dominant retinitis pigmentosa (adRP). We report seven patients from six unrelated families with a neurodevelopmental disorder associated with developmental delay, intellectual disability, structural brain abnormality, and visual impairments in whom we identified four novel, de novo missense variants in the N-terminal half of HK1. Hexokinase activity in red blood cells of two patients was normal, suggesting that the disease mechanism is not due to loss of hexokinase enzymatic activity.
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http://dx.doi.org/10.1038/s41431-019-0366-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6777464PMC
July 2019

Author Correction: CHD3 helicase domain mutations cause a neurodevelopmental syndrome with macrocephaly and impaired speech and language.

Nat Commun 2019 02 15;10(1):883. Epub 2019 Feb 15.

CHU Sainte-Justine Research Center, Montreal, QC, H3T 1C5, Canada.

The original version of this Article contained an error in the spelling of the author Laurence Faivre, which was incorrectly given as Laurence Faive. This has now been corrected in both the PDF and HTML versions of the Article.
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http://dx.doi.org/10.1038/s41467-019-08800-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6377600PMC
February 2019

Variants in TCF20 in neurodevelopmental disability: description of 27 new patients and review of literature.

Genet Med 2019 09 11;21(9):2036-2042. Epub 2019 Feb 11.

GeneDx, Gaithersburg, MD, USA.

Purpose: To define the clinical characteristics of patients with variants in TCF20, we describe 27 patients, 26 of whom were identified via exome sequencing. We compare detailed clinical data with 17 previously reported patients.

Methods: Patients were ascertained through molecular testing laboratories performing exome sequencing (and other testing) with orthogonal confirmation; collaborating referring clinicians provided detailed clinical information.

Results: The cohort of 27 patients all had novel variants, and ranged in age from 2 to 68 years. All had developmental delay/intellectual disability. Autism spectrum disorders/autistic features were reported in 69%, attention disorders or hyperactivity in 67%, craniofacial features (no recognizable facial gestalt) in 67%, structural brain anomalies in 24%, and seizures in 12%. Additional features affecting various organ systems were described in 93%. In a majority of patients, we did not observe previously reported findings of postnatal overgrowth or craniosynostosis, in comparison with earlier reports.

Conclusion: We provide valuable data regarding the prognosis and clinical manifestations of patients with variants in TCF20.
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http://dx.doi.org/10.1038/s41436-019-0454-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7171701PMC
September 2019

Lamin B receptor-related disorder is associated with a spectrum of skeletal dysplasia phenotypes.

Bone 2019 03 15;120:354-363. Epub 2018 Nov 15.

Department of Pediatrics, Division of Medical Genetics, Washington University School of Medicine, St. Louis, MO, USA. Electronic address:

LBR (Lamin B Receptor) encodes a bifunctional protein important for cholesterol biosynthesis and heterochromatin organization on the inner nuclear membrane. Pathogenic variants in LBR are associated with marked phenotypic variability, ranging from the benign Pelger-Huët anomaly to lethal Greenberg Dysplasia. We performed trio exome sequencing (ES) on two patients with atypical variants of skeletal dysplasia and their unaffected parents. Patient 1 exhibited frontal bossing, mid-face hypoplasia, short stature with rhizomelic limb shortening, and relative macrocephaly at birth. Although remained short, Patient 1 later showed spontaneous improvement in her skeletal findings. Exome sequencing revealed two novel variants in LBR, c.1504C > G (p.Arg502Gly) in exon 12 and c.1748G > T (p.Arg583Leu) in exon 14, which were inherited from her unaffected father and mother, respectively. Sterol analysis revealed an increased level of cholesta‑8,14‑dien‑3β‑ol to 2.9% of total sterols, consistent with a functional deficiency of 3β‑hydroxysterol Δ14‑reductase. Patient 2 presented at birth with short stature and marked rhizomelic limb shortening but later exhibited decreasing severity of shortening of the long bones and improvement in the radiographic skeletal abnormalities although he continued to be significantly short at age 10 years. Exome sequencing revealed that Patient 2 is homozygous for a pathogenic variant c.1534C > T (p.Arg512Trp) in exon 12 of LBR, which was inherited from his unaffected consanguineous parents. This report provides further evidence for a phenotypic spectrum of LBR-associated disorders and expands the genotypic spectrum by describing 3 novel disease-causing variants that have not been previously associated with a disease. Moreover, our data on Patient 1 demonstrate that variants throughout the gene appear to influence both the sterol reductase and nuclear functions of LBR.
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http://dx.doi.org/10.1016/j.bone.2018.11.006DOI Listing
March 2019

CHD3 helicase domain mutations cause a neurodevelopmental syndrome with macrocephaly and impaired speech and language.

Nat Commun 2018 11 5;9(1):4619. Epub 2018 Nov 5.

CHU Sainte-Justine Research Center, Montreal, QC H3T 1C5, Canada.

Chromatin remodeling is of crucial importance during brain development. Pathogenic alterations of several chromatin remodeling ATPases have been implicated in neurodevelopmental disorders. We describe an index case with a de novo missense mutation in CHD3, identified during whole genome sequencing of a cohort of children with rare speech disorders. To gain a comprehensive view of features associated with disruption of this gene, we use a genotype-driven approach, collecting and characterizing 35 individuals with de novo CHD3 mutations and overlapping phenotypes. Most mutations cluster within the ATPase/helicase domain of the encoded protein. Modeling their impact on the three-dimensional structure demonstrates disturbance of critical binding and interaction motifs. Experimental assays with six of the identified mutations show that a subset directly affects ATPase activity, and all but one yield alterations in chromatin remodeling. We implicate de novo CHD3 mutations in a syndrome characterized by intellectual disability, macrocephaly, and impaired speech and language.
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http://dx.doi.org/10.1038/s41467-018-06014-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6218476PMC
November 2018

Correction: TANGO2: expanding the clinical phenotype and spectrum of pathogenic variants.

Genet Med 2019 Aug;21(8):1899

Department of Pediatrics, University of Washington, Seattle, Washington, USA.

The original version of this Article contained an error in the spelling of the author J. Lawrence Merritt, which was incorrectly given as Lawrence Merritt. This has now been corrected in both the PDF and HTML versions of the Article.
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http://dx.doi.org/10.1038/s41436-018-0336-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7608300PMC
August 2019

A Recurrent De Novo Heterozygous COG4 Substitution Leads to Saul-Wilson Syndrome, Disrupted Vesicular Trafficking, and Altered Proteoglycan Glycosylation.

Am J Hum Genet 2018 10;103(4):553-567

Human Genetics Program, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA 92037, USA.

The conserved oligomeric Golgi (COG) complex is involved in intracellular vesicular transport, and is composed of eight subunits distributed in two lobes, lobe A (COG1-4) and lobe B (COG5-8). We describe fourteen individuals with Saul-Wilson syndrome, a rare form of primordial dwarfism with characteristic facial and radiographic features. All affected subjects harbored heterozygous de novo variants in COG4, giving rise to the same recurrent amino acid substitution (p.Gly516Arg). Affected individuals' fibroblasts, whose COG4 mRNA and protein were not decreased, exhibited delayed anterograde vesicular trafficking from the ER to the Golgi and accelerated retrograde vesicular recycling from the Golgi to the ER. This altered steady-state equilibrium led to a decrease in Golgi volume, as well as morphologic abnormalities with collapse of the Golgi stacks. Despite these abnormalities of the Golgi apparatus, protein glycosylation in sera and fibroblasts from affected subjects was not notably altered, but decorin, a proteoglycan secreted into the extracellular matrix, showed altered Golgi-dependent glycosylation. In summary, we define a specific heterozygous COG4 substitution as the molecular basis of Saul-Wilson syndrome, a rare skeletal dysplasia distinct from biallelic COG4-CDG.
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http://dx.doi.org/10.1016/j.ajhg.2018.09.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6174323PMC
October 2018

TANGO2: expanding the clinical phenotype and spectrum of pathogenic variants.

Genet Med 2019 03 24;21(3):601-607. Epub 2018 Sep 24.

Department of Pediatrics, University of Washington, Seattle, Washington, USA.

Purpose: TANGO2-related disorders were first described in 2016 and prior to this publication, only 15 individuals with TANGO2-related disorder were described in the literature. Primary features include metabolic crisis with rhabdomyolysis, encephalopathy, intellectual disability, seizures, and cardiac arrhythmias. We assess whether genotype and phenotype of TANGO2-related disorder has expanded since the initial discovery and determine the efficacy of exome sequencing (ES) as a diagnostic tool for detecting variants.

Methods: We present a series of 14 individuals from 11 unrelated families with complex medical and developmental histories, in whom ES or microarray identified compound heterozygous or homozygous variants in TANGO2.

Results: The initial presentation of patients with TANGO2-related disorders can be variable, including primarily neurological presentations. We expand the phenotype and genotype for TANGO2, highlighting the variability of the disorder.

Conclusion: TANGO2-related disorders can have a more diverse clinical presentation than previously anticipated. We illustrate the utility of routine ES data reanalysis whereby discovery of novel disease genes can lead to a diagnosis in previously unsolved cases and the need for additional copy-number variation analysis when ES is performed.
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http://dx.doi.org/10.1038/s41436-018-0137-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6752277PMC
March 2019

Variable cardiovascular phenotypes associated with SMAD2 pathogenic variants.

Hum Mutat 2018 12 24;39(12):1875-1884. Epub 2018 Sep 24.

Division of Genetics and Genomic Medicine, Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri.

SMAD2 is a downstream effector in the TGF-β signaling pathway, which is important for pattern formation and tissue differentiation. Pathogenic variants in SMAD2 have been reported in association with arterial aneurysms and dissections and in large cohorts of subjects with complex congenital heart disease (CHD). We used whole exome sequencing (WES) to investigate the molecular cause of CHD and other congenital anomalies in three probands and of an arterial aneurysm in an additional patient. Patients 1 and 2 presented with complex CHD, developmental delay, seizures, dysmorphic features, short stature, and poor weight gain. Patient 3 was a fetus with complex CHD and heterotaxy. The fourth patient is an adult female with aortic root aneurysm and physical features suggestive of a connective tissue disorder. WES identified pathogenic truncating variants, a splice variant, and a predicted deleterious missense variant in SMAD2. We compare the phenotypes and genotypes in our patients with previously reported cases. Our data suggest two distinct phenotypes associated with pathogenic variants in SMAD2: complex CHD with or without laterality defects and other congenital anomalies, and a late-onset vascular phenotype characterized by arterial aneurysms with connective tissue abnormalities.
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http://dx.doi.org/10.1002/humu.23627DOI Listing
December 2018

De novo missense variants in MEIS2 recapitulate the microdeletion phenotype of cardiac and palate abnormalities, developmental delay, intellectual disability and dysmorphic features.

Am J Med Genet A 2018 09 28;176(9):1845-1851. Epub 2018 Jul 28.

GeneDx, Gaithersburg, Maryland.

Gross deletions involving the MEIS2 gene have been described in a small number of patients with overlapping phenotypes of atrial or ventricular septal defects, cleft palate, and variable developmental delays and intellectual disability. Non-specific dysmorphic features were noted in some patients, including broad forehead with high anterior hairline, arched eyebrows, thin or tented upper lip, and short philtrum. Recently, a patient with a de novo single amino acid deletion, c.998_1000delGAA (p.Arg333del), and a patient with a de novo nonsense variant, (c.611C>G, p.Ser204*), were reported with a similar, but apparently more severe phenotypes. Clinical whole exome sequencing (WES) performed at our clinical molecular diagnostic laboratory identified four additional patients with predicted damaging de novo MEIS2 missense variants. Our patients' features closely resembled those previously reported in patients with gross deletions, but also included some less commonly reported features, such as autism spectrum disorder, hearing loss, and short stature, as well as features that may be unique to nucleotide-level variants, such as hypotonia, failure to thrive, gastrointestinal, skeletal, limb, and skin abnormalities. All of the observed missense variants, Pro302Leu, Gln322Leu, Arg331Lys, and Val335Ala, are located in the functionally important MEIS2 homeodomain. Pro302Leu is found in the region between helix 1 and helix 2, while the other three are located in the DNA-binding helix 3. To our knowledge, these are the first described de novo missense variants in MEIS2, expanding the known mutation spectrum of the newly recognized human disorder caused by aberrations in this gene.
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http://dx.doi.org/10.1002/ajmg.a.40368DOI Listing
September 2018

Missense Variants in RHOBTB2 Cause a Developmental and Epileptic Encephalopathy in Humans, and Altered Levels Cause Neurological Defects in Drosophila.

Am J Hum Genet 2018 01 21;102(1):44-57. Epub 2017 Dec 21.

Institute of Human Genetics, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91054 Erlangen, Germany. Electronic address:

Although the role of typical Rho GTPases and other Rho-linked proteins in synaptic plasticity and cognitive function and dysfunction is widely acknowledged, the role of atypical Rho GTPases (such as RHOBTB2) in neurodevelopment has barely been characterized. We have now identified de novo missense variants clustering in the BTB-domain-encoding region of RHOBTB2 in ten individuals with a similar phenotype, including early-onset epilepsy, severe intellectual disability, postnatal microcephaly, and movement disorders. Three of the variants were recurrent. Upon transfection of HEK293 cells, we found that mutant RHOBTB2 was more abundant than the wild-type, most likely because of impaired degradation in the proteasome. Similarly, elevated amounts of the Drosophila ortholog RhoBTB in vivo were associated with seizure susceptibility and severe locomotor defects. Knockdown of RhoBTB in the Drosophila dendritic arborization neurons resulted in a decreased number of dendrites, thus suggesting a role of RhoBTB in dendritic development. We have established missense variants in the BTB-domain-encoding region of RHOBTB2 as causative for a developmental and epileptic encephalopathy and have elucidated the role of atypical Rho GTPase RhoBTB in Drosophila neurological function and possibly dendrite development.
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http://dx.doi.org/10.1016/j.ajhg.2017.11.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5777381PMC
January 2018

The spectrum of DNMT3A variants in Tatton-Brown-Rahman syndrome overlaps with that in hematologic malignancies.

Am J Med Genet A 2017 Nov 21;173(11):3022-3028. Epub 2017 Sep 21.

Department of Pediatrics, University of Utah School of Medicine, Salt Lake City, Utah.

De novo, germline variants in DNMT3A cause Tatton-Brown-Rahman syndrome (TBRS). This condition is characterized by overgrowth, distinctive facial appearance, and intellectual disability. Somatic DNMT3A variants frequently occur in hematologic malignances, particularly acute myeloid leukemia. The Arg882 residue is the most common site of somatic DNMT3A variants, and has also been altered in patients with TBRS. Here we present three additional patients with this disorder attributed to DNMT3A germline variants that disrupt the Arg882 codon, suggesting that this codon may be a germline mutation hotspot in this disorder. Furthermore, based on the investigation of previously reported variants in patients with TBRS, we found overlap in the spectrum of DNMT3A variants observed in this disorder and somatic variants in hematological malignancies.
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http://dx.doi.org/10.1002/ajmg.a.38485DOI Listing
November 2017

WDR26 Haploinsufficiency Causes a Recognizable Syndrome of Intellectual Disability, Seizures, Abnormal Gait, and Distinctive Facial Features.

Am J Hum Genet 2017 Jul;101(1):139-148

Division of Genetics, Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA; Department of Pediatrics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address:

We report 15 individuals with de novo pathogenic variants in WDR26. Eleven of the individuals carry loss-of-function mutations, and four harbor missense substitutions. These 15 individuals comprise ten females and five males, and all have intellectual disability with delayed speech, a history of febrile and/or non-febrile seizures, and a wide-based, spastic, and/or stiff-legged gait. These subjects share a set of common facial features that include a prominent maxilla and upper lip that readily reveal the upper gingiva, widely spaced teeth, and a broad nasal tip. Together, these features comprise a recognizable facial phenotype. We compared these features with those of chromosome 1q41q42 microdeletion syndrome, which typically contains WDR26, and noted that clinical features are consistent between the two subsets, suggesting that haploinsufficiency of WDR26 contributes to the pathology of 1q41q42 microdeletion syndrome. Consistent with this, WDR26 loss-of-function single-nucleotide mutations identified in these subjects lead to nonsense-mediated decay with subsequent reduction of RNA expression and protein levels. We derived a structural model of WDR26 and note that missense variants identified in these individuals localize to highly conserved residues of this WD-40-repeat-containing protein. Given that WDR26 mutations have been identified in ∼1 in 2,000 of subjects in our clinical cohorts and that WDR26 might be poorly annotated in exome variant-interpretation pipelines, we would anticipate that this disorder could be more common than currently appreciated.
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http://dx.doi.org/10.1016/j.ajhg.2017.06.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5501873PMC
July 2017

Neuroligin 2 nonsense variant associated with anxiety, autism, intellectual disability, hyperphagia, and obesity.

Am J Med Genet A 2017 Jan 16;173(1):213-216. Epub 2016 Nov 16.

Division of Genetics and Genomic Medicine, Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri.

Neuroligins are post-synaptic, cellular adhesion molecules implicated in synaptic formation and function. NLGN2 is strongly linked to inhibitory, GABAergic signaling and is crucial for maintaining the excitation-inhibition balance in the brain. Disruption of the excitation-inhibition balance is associated with neuropsychiatric disease. In animal models, altered NLGN2 expression causes anxiety, developmental delay, motor discoordination, social impairment, aggression, and sensory processing defects. In humans, mutations in NLGN3 and NLGN4 are linked to autism and schizophrenia; NLGN2 missense variants are implicated in schizophrenia. Copy number variants encompassing NLGN2 on 17p13.1 are associated with autism, intellectual disability, metabolic syndrome, diabetes, and dysmorphic features, but an isolated NLGN2 nonsense variant has not yet been described in humans. Here, we describe a 15-year-old male with severe anxiety, obsessive-compulsive behaviors, developmental delay, autism, obesity, macrocephaly, and some dysmorphic features. Exome sequencing identified a heterozygous, de novo, c.441C>A p.(Tyr147Ter) variant in NLGN2 that is predicted to cause loss of normal protein function. This is the first report of an NLGN2 nonsense variant in humans, adding to the accumulating evidence that links synaptic proteins with a spectrum of neurodevelopmental phenotypes. © 2016 Wiley Periodicals, Inc.
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http://dx.doi.org/10.1002/ajmg.a.37977DOI Listing
January 2017

The expanding clinical phenotype of Bosch-Boonstra-Schaaf optic atrophy syndrome: 20 new cases and possible genotype-phenotype correlations.

Genet Med 2016 11 17;18(11):1143-1150. Epub 2016 Mar 17.

Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA.

Purpose: Bosch-Boonstra-Schaaf optic atrophy syndrome (BBSOAS) is an autosomal-dominant disorder characterized by optic atrophy and intellectual disability caused by loss-of-function mutations in NR2F1. We report 20 new individuals with BBSOAS, exploring the spectrum of clinical phenotypes and assessing potential genotype-phenotype correlations.

Methods: Clinical features of individuals with pathogenic NR2F1 variants were evaluated by review of medical records. The functional relevance of coding nonsynonymous NR2F1 variants was assessed with a luciferase assay measuring the impact on transcriptional activity. The effects of two start codon variants on protein expression were evaluated by western blot analysis.

Results: We recruited 20 individuals with novel pathogenic NR2F1 variants (seven missense variants, five translation initiation variants, two frameshifting insertions/deletions, one nonframeshifting insertion/deletion, and five whole-gene deletions). All the missense variants were found to impair transcriptional activity. In addition to visual and cognitive deficits, individuals with BBSOAS manifested hypotonia (75%), seizures (40%), autism spectrum disorder (35%), oromotor dysfunction (60%), thinning of the corpus callosum (53%), and hearing defects (20%).

Conclusion: BBSOAS encompasses a broad range of clinical phenotypes. Functional studies help determine the severity of novel NR2F1 variants. Some genotype-phenotype correlations seem to exist, with missense mutations in the DNA-binding domain causing the most severe phenotypes.Genet Med 18 11, 1143-1150.
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http://dx.doi.org/10.1038/gim.2016.18DOI Listing
November 2016

Biallelic Mutations in TBCD, Encoding the Tubulin Folding Cofactor D, Perturb Microtubule Dynamics and Cause Early-Onset Encephalopathy.

Am J Hum Genet 2016 Oct 22;99(4):962-973. Epub 2016 Sep 22.

Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome 00146, Italy. Electronic address:

Microtubules are dynamic cytoskeletal elements coordinating and supporting a variety of neuronal processes, including cell division, migration, polarity, intracellular trafficking, and signal transduction. Mutations in genes encoding tubulins and microtubule-associated proteins are known to cause neurodevelopmental and neurodegenerative disorders. Growing evidence suggests that altered microtubule dynamics may also underlie or contribute to neurodevelopmental disorders and neurodegeneration. We report that biallelic mutations in TBCD, encoding one of the five co-chaperones required for assembly and disassembly of the αβ-tubulin heterodimer, the structural unit of microtubules, cause a disease with neurodevelopmental and neurodegenerative features characterized by early-onset cortical atrophy, secondary hypomyelination, microcephaly, thin corpus callosum, developmental delay, intellectual disability, seizures, optic atrophy, and spastic quadriplegia. Molecular dynamics simulations predicted long-range and/or local structural perturbations associated with the disease-causing mutations. Biochemical analyses documented variably reduced levels of TBCD, indicating relative instability of mutant proteins, and defective β-tubulin binding in a subset of the tested mutants. Reduced or defective TBCD function resulted in decreased soluble α/β-tubulin levels and accelerated microtubule polymerization in fibroblasts from affected subjects, demonstrating an overall shift toward a more rapidly growing and stable microtubule population. These cells displayed an aberrant mitotic spindle with disorganized, tangle-shaped microtubules and reduced aster formation, which however did not alter appreciably the rate of cell proliferation. Our findings establish that defective TBCD function underlies a recognizable encephalopathy and drives accelerated microtubule polymerization and enhanced microtubule stability, underscoring an additional cause of altered microtubule dynamics with impact on neuronal function and survival in the developing brain.
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http://dx.doi.org/10.1016/j.ajhg.2016.08.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5065658PMC
October 2016

De Novo Mutations in SON Disrupt RNA Splicing of Genes Essential for Brain Development and Metabolism, Causing an Intellectual-Disability Syndrome.

Am J Hum Genet 2016 09 18;99(3):711-719. Epub 2016 Aug 18.

Mitchell Cancer Institute, University of South Alabama, Mobile, AL 36604, USA; Department of Biochemistry and Molecular Biology, College of Medicine, University of South Alabama, Mobile, AL 36688, USA. Electronic address:

The overall understanding of the molecular etiologies of intellectual disability (ID) and developmental delay (DD) is increasing as next-generation sequencing technologies identify genetic variants in individuals with such disorders. However, detailed analyses conclusively confirming these variants, as well as the underlying molecular mechanisms explaining the diseases, are often lacking. Here, we report on an ID syndrome caused by de novo heterozygous loss-of-function (LoF) mutations in SON. The syndrome is characterized by ID and/or DD, malformations of the cerebral cortex, epilepsy, vision problems, musculoskeletal abnormalities, and congenital malformations. Knockdown of son in zebrafish resulted in severe malformation of the spine, brain, and eyes. Importantly, analyses of RNA from affected individuals revealed that genes critical for neuronal migration and cortex organization (TUBG1, FLNA, PNKP, WDR62, PSMD3, and HDAC6) and metabolism (PCK2, PFKL, IDH2, ACY1, and ADA) are significantly downregulated because of the accumulation of mis-spliced transcripts resulting from erroneous SON-mediated RNA splicing. Our data highlight SON as a master regulator governing neurodevelopment and demonstrate the importance of SON-mediated RNA splicing in human development.
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http://dx.doi.org/10.1016/j.ajhg.2016.06.029DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5011044PMC
September 2016

Mutation in SLC6A9 encoding a glycine transporter causes a novel form of non-ketotic hyperglycinemia in humans.

Hum Genet 2016 Nov 1;135(11):1263-1268. Epub 2016 Aug 1.

GeneDx, Gaithersburg, MD, 20877, USA.

Glycine cleavage system (GCS) catalyzes the degradation of glycine and disruption of its components encoded by GLDC, AMT and GCSH are the only known causes of glycine encephalopathy, also known as non-ketotic hyperglycinemia (NKH). In this report, we describe a consanguineous family with one child who presented with NKH, but harbored no pathogenic variants in any of the three genes linked to this condition. Whole-exome sequencing revealed a novel homozygous missense variant in exon 9 of SLC6A9 NM_201649.3: c.1219 A>G (p.Ser407Gly) that segregates with the disease within the family. This variant replaces the highly conserved S407 in the ion-binding site of this glycine transporter and is predicted to disrupt its function. In murine model, knockout of Slc6a9 is associated with equivalent phenotype of NKH, namely respiratory distress and hypotonia. This is the first demonstration that mutation of the glycine transporter can be associated with NKH in humans.
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http://dx.doi.org/10.1007/s00439-016-1719-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5052303PMC
November 2016

De novo pathogenic variants in CHAMP1 are associated with global developmental delay, intellectual disability, and dysmorphic facial features.

Cold Spring Harb Mol Case Stud 2016 Jan;2(1):a000661

Department of Pediatrics, Columbia University Medical Center, New York, New York 10032, USA;; Department of Medicine, Columbia University Medical Center, New York, New York 10032, USA.

We identified five unrelated individuals with significant global developmental delay and intellectual disability (ID), dysmorphic facial features and frequent microcephaly, and de novo predicted loss-of-function variants in chromosome alignment maintaining phosphoprotein 1 (CHAMP1). Our findings are consistent with recently reported de novo mutations in CHAMP1 in five other individuals with similar features. CHAMP1 is a zinc finger protein involved in kinetochore-microtubule attachment and is required for regulating the proper alignment of chromosomes during metaphase in mitosis. Mutations in CHAMP1 may affect cell division and hence brain development and function, resulting in developmental delay and ID.
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http://dx.doi.org/10.1101/mcs.a000661DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4849844PMC
January 2016