Publications by authors named "Mirna Assoum"

19 Publications

  • Page 1 of 1

Genotype-first in a cohort of 95 fetuses with multiple congenital abnormalities: when exome sequencing reveals unexpected fetal phenotype-genotype correlations.

J Med Genet 2020 Jul 30. Epub 2020 Jul 30.

UFR Des Sciences de Santé, INSERM-Université de Bourgogne UMR1231 GAD « Génétique des Anomalies du Développement », FHU-TRANSLAD, Dijon, France

Purpose: Molecular diagnosis based on singleton exome sequencing (sES) is particularly challenging in fetuses with multiple congenital abnormalities (MCA). Indeed, some studies reveal a diagnostic yield of about 20%, far lower than in live birth individuals showing developmental abnormalities (30%), suggesting that standard analyses, based on the correlation between clinical hallmarks described in postnatal syndromic presentations and genotype, may underestimate the impact of the genetic variants identified in fetal analyses.

Methods: We performed sES in 95 fetuses with MCA. Blind to phenotype, we applied a genotype-first approach consisting of combined analyses based on variants annotation and bioinformatics predictions followed by reverse phenotyping. Initially applied to OMIM-morbid genes, analyses were then extended to all genes. We complemented our approach by using reverse phenotyping, variant segregation analysis, bibliographic search and data sharing in order to establish the clinical significance of the prioritised variants.

Results: sES rapidly identified causal variant in 24/95 fetuses (25%), variants of unknown significance in OMIM genes in 8/95 fetuses (8%) and six novel candidate genes in 6/95 fetuses (6%).

Conclusions: This method, based on a genotype-first approach followed by reverse phenotyping, shed light on unexpected fetal phenotype-genotype correlations, emphasising the relevance of prenatal studies to reveal extreme clinical presentations associated with well-known Mendelian disorders.
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http://dx.doi.org/10.1136/jmedgenet-2020-106867DOI Listing
July 2020

A genomics approach to male infertility.

Genet Med 2020 Dec 28;22(12):1967-1975. Epub 2020 Jul 28.

Department of Genetics, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia.

Purpose: Male infertility remains poorly understood at the molecular level. We aimed in this study to investigate the yield of a "genomics first" approach to male infertility.

Methods: Patients with severe oligospermia and nonobstructive azoospermia were investigated using exome sequencing (ES) in parallel with the standard practice of chromosomal analysis.

Results: In 285 patients, 10.5% (n = 30) had evidence of chromosomal aberrations while nearly a quarter (n = 69; 24.2%) had a potential monogenic form of male infertility. The latter ranged from variants in genes previously reported to cause male infertility with or without other phenotypes in humans (24 patients; 8.4%) to those in novel candidate genes reported in this study (37 patients; 12.9%). The 33 candidate genes have biological links to male germ cell development including compatible mouse knockouts, and a few (TERB1 [CCDC79], PIWIL2, MAGEE2, and ZSWIM7) were found to be independently mutated in unrelated patients in our cohort. We also found that male infertility can be the sole or major phenotypic expression of a number of genes that are known to cause multisystemic manifestations in humans (n = 9 patients; 3.1%).

Conclusion: The standard approach to male infertility overlooks the significant contribution of monogenic causes to this important clinical entity.
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http://dx.doi.org/10.1038/s41436-020-0916-0DOI Listing
December 2020

Excess of de novo variants in genes involved in chromatin remodelling in patients with marfanoid habitus and intellectual disability.

J Med Genet 2020 07 10;57(7):466-474. Epub 2020 Apr 10.

INSERM, U1231, Génétique des Anomalies du Développement, Université de Bourgogne Franche-Comté, UMR Lipides, Nutrition, Dijon, France

Purpose: Marfanoid habitus (MH) combined with intellectual disability (ID) (MHID) is a clinically and genetically heterogeneous presentation. The combination of array CGH and targeted sequencing of genes responsible for Marfan or Lujan-Fryns syndrome explain no more than 20% of subjects.

Methods: To further decipher the genetic basis of MHID, we performed exome sequencing on a combination of trio-based (33 subjects) or single probands (31 subjects), of which 61 were sporadic.

Results: We identified eight genes with de novo variants (DNVs) in at least two unrelated individuals ( and ). Using simulation models, we showed that five genes ( and ) met conservative Bonferroni genomewide significance for an excess of the observed de novo point variants. Overall, at least one pathogenic or likely pathogenic variant was identified in 54.7% of subjects (35/64). These variants fell within 27 genes previously associated with Mendelian disorders, including and , which are known to be mutated in overgrowth syndromes.

Conclusion: We demonstrated that DNVs were enriched in chromatin remodelling (p=2×10) and genes regulated by the fragile X mental retardation protein (p=3×10), highlighting overlapping genetic mechanisms between MHID and related neurodevelopmental disorders.
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http://dx.doi.org/10.1136/jmedgenet-2019-106425DOI Listing
July 2020

Novel KIAA1033/WASHC4 mutations in three patients with syndromic intellectual disability and a review of the literature.

Am J Med Genet A 2020 04 18;182(4):792-797. Epub 2020 Jan 18.

UMR-Inserm 1231 GAD team, Génétique des Anomalies du développement, Université de Bourgogne Franche-Comté, Dijon, France.

In 2011, KIAA1033/WASHC4 was associated with autosomal recessive intellectual disability (ARID) in a large consanguineous family comprising seven affected individuals with moderate ID and short stature. Since then, no other cases of KIAA1033 variants have been reported. Here we describe three additional patients (from two unrelated families) with syndromic ID due to compound heterozygous KIAA1033 variants ascertained by exome sequencing (ES). Two sisters, aged 4 and 5.5 years, had a stop-gain and a missense variants, each inherited from one parent (p.(Gln442*) and p.(Asp1048Gly)). Both had learning disabilities, macrocephaly, dysmorphic features, skeletal anomalies, and subependymal heterotopic nodules. In addition, the younger sibling had a congenital absence of the right internal carotid and bilateral sensorineural hearing loss. The third patient was aged 34 years and had two missense variants, one inherited from each parent (p.(Lys1079Arg) and p.(His503Arg)). This patient presented with mild ID, short stature, and microcephaly. KIAA1033 encodes a large protein (WASHC4), which is part of the WASH complex. The WASH complex is involved in the regulation of the fission of tubules that serve as transport intermediates during endosome sorting. Another member of the WASH complex, KIAA0196/WASHC5, has already been implicated in ARID with brain and cardiac malformations, under the designation of 3C or Ritscher-Schinzel syndrome (MIM#20210). ES has proved efficient for finding replications of genes with insufficient data in the literature to be defined as new OMIM genes. We conclude that KIAA1033 is responsible for a heterogeneous ARID phenotype, and additional description will be needed to refine the clinical phenotype.
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http://dx.doi.org/10.1002/ajmg.a.61487DOI Listing
April 2020

Lessons Learned from Large-Scale, First-Tier Clinical Exome Sequencing in a Highly Consanguineous Population.

Authors:
Dorota Monies Mohammed Abouelhoda Mirna Assoum Nabil Moghrabi Rafiullah Rafiullah Naif Almontashiri Mohammed Alowain Hamad Alzaidan Moeen Alsayed Shazia Subhani Edward Cupler Maha Faden Amal Alhashem Alya Qari Aziza Chedrawi Hisham Aldhalaan Wesam Kurdi Sameena Khan Zuhair Rahbeeni Maha Alotaibi Ewa Goljan Hadeel Elbardisy Mohamed ElKalioby Zeeshan Shah Hibah Alruwaili Amal Jaafar Ranad Albar Asma Akilan Hamsa Tayeb Asma Tahir Mohammed Fawzy Mohammed Nasr Shaza Makki Abdullah Alfaifi Hanna Akleh Suad Yamani Dalal Bubshait Mohammed Mahnashi Talal Basha Afaf Alsagheir Musad Abu Khaled Khalid Alsaleem Maisoon Almugbel Manal Badawi Fahad Bashiri Saeed Bohlega Raashida Sulaiman Ehab Tous Syed Ahmed Talal Algoufi Hamoud Al-Mousa Emadia Alaki Susan Alhumaidi Hadeel Alghamdi Malak Alghamdi Ahmed Sahly Shapar Nahrir Ali Al-Ahmari Hisham Alkuraya Ali Almehaidib Mohammed Abanemai Fahad Alsohaibaini Bandar Alsaud Rand Arnaout Ghada M H Abdel-Salam Hasan Aldhekri Suzan AlKhater Khalid Alqadi Essam Alsabban Turki Alshareef Khalid Awartani Hanaa Banjar Nada Alsahan Ibraheem Abosoudah Abdullah Alashwal Wajeeh Aldekhail Sami Alhajjar Sulaiman Al-Mayouf Abdulaziz Alsemari Walaa Alshuaibi Saeed Altala Abdulhadi Altalhi Salah Baz Muddathir Hamad Tariq Abalkhail Badi Alenazi Alya Alkaff Fahad Almohareb Fuad Al Mutairi Mona Alsaleh Abdullah Alsonbul Somaya Alzelaye Shakir Bahzad Abdulaziz Bin Manee Ola Jarrad Neama Meriki Bassem Albeirouti Amal Alqasmi Mohammed AlBalwi Nawal Makhseed Saeed Hassan Isam Salih Mustafa A Salih Marwan Shaheen Saadeh Sermin Shamsad Shahrukh Shahrukh Hashmi Ayman Shawli Ameen Tajuddin Abdullah Tamim Ahmed Alnahari Ibrahim Ghemlas Maged Hussein Sami Wali Hatem Murad Brian F Meyer Fowzan S Alkuraya

Am J Hum Genet 2019 Oct;105(4):879

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http://dx.doi.org/10.1016/j.ajhg.2019.09.019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6817532PMC
October 2019

Increased diagnostic and new genes identification outcome using research reanalysis of singleton exome sequencing.

Eur J Hum Genet 2019 10 23;27(10):1519-1531. Epub 2019 Jun 23.

Inserm UMR 1231 GAD, Genetics of Developmental disorders, Université de Bourgogne-Franche Comté, FHU TRANSLAD, Dijon, France.

In clinical exome sequencing (cES), the American College of Medical Genetics and Genomics recommends limiting variant interpretation to established human-disease genes. The diagnostic yield of cES in intellectual disability and/or multiple congenital anomalies (ID/MCA) is currently about 30%. Though the results may seem acceptable for rare diseases, they mean that 70% of affected individuals remain genetically undiagnosed. Further analysis extended to all mutated genes in a research environment is a valuable strategy for improving diagnostic yields. This study presents the results of systematic research reanalysis of negative cES in a cohort of 313 individuals with ID/MCA. We identified 17 new genes not related to human disease, implicated 22 non-OMIM disease-causing genes recently or previously rarely related to disease, and described 1 new phenotype associated with a known gene. Twenty-six candidate genes were identified and are waiting for future recurrence. Overall, we diagnose 15% of the individuals with initial negative cES, increasing the diagnostic yield from 30% to more than 40% (or 46% if strong candidate genes are considered). This study demonstrates the power of such extended research reanalysis to increase scientific knowledge of rare diseases. These novel findings can then be applied in the field of diagnostics.
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http://dx.doi.org/10.1038/s41431-019-0442-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6777617PMC
October 2019

Lessons Learned from Large-Scale, First-Tier Clinical Exome Sequencing in a Highly Consanguineous Population.

Authors:
Dorota Monies Mohammed Abouelhoda Mirna Assoum Nabil Moghrabi Rafiullah Rafiullah Naif Almontashiri Mohammed Alowain Hamad Alzaidan Moeen Alsayed Shazia Subhani Edward Cupler Maha Faden Amal Alhashem Alya Qari Aziza Chedrawi Hisham Aldhalaan Wesam Kurdi Sameena Khan Zuhair Rahbeeni Maha Alotaibi Ewa Goljan Hadeel Elbardisy Mohamed ElKalioby Zeeshan Shah Hibah Alruwaili Amal Jaafar Ranad Albar Asma Akilan Hamsa Tayeb Asma Tahir Mohammed Fawzy Mohammed Nasr Shaza Makki Abdullah Alfaifi Hanna Akleh Suad Yamani Dalal Bubshait Mohammed Mahnashi Talal Basha Afaf Alsagheir Musad Abu Khaled Khalid Alsaleem Maisoon Almugbel Manal Badawi Fahad Bashiri Saeed Bohlega Raashida Sulaiman Ehab Tous Syed Ahmed Talal Algoufi Hamoud Al-Mousa Emadia Alaki Susan Alhumaidi Hadeel Alghamdi Malak Alghamdi Ahmed Sahly Shapar Nahrir Ali Al-Ahmari Hisham Alkuraya Ali Almehaidib Mohammed Abanemai Fahad Alsohaibaini Bandar Alsaud Rand Arnaout Ghada M H Abdel-Salam Hasan Aldhekri Suzan AlKhater Khalid Alqadi Essam Alsabban Turki Alshareef Khalid Awartani Hanaa Banjar Nada Alsahan Ibraheem Abosoudah Abdullah Alashwal Wajeeh Aldekhail Sami Alhajjar Sulaiman Al-Mayouf Abdulaziz Alsemari Walaa Alshuaibi Saeed Altala Abdulhadi Altalhi Salah Baz Muddathir Hamad Tariq Abalkhail Badi Alenazi Alya Alkaff Fahad Almohareb Fuad Al Mutairi Mona Alsaleh Abdullah Alsonbul Somaya Alzelaye Shakir Bahzad Abdulaziz Bin Manee Ola Jarrad Neama Meriki Bassem Albeirouti Amal Alqasmi Mohammed AlBalwi Nawal Makhseed Saeed Hassan Isam Salih Mustafa A Salih Marwan Shaheen Saadeh Sermin Shamsad Shahrukh Shahrukh Hashmi Ayman Shawli Ameen Tajuddin Abdullah Tamim Ahmed Alnahari Ibrahim Ghemlas Maged Hussein Sami Wali Hatem Murad Brian F Meyer Fowzan S Alkuraya

Am J Hum Genet 2019 06 23;104(6):1182-1201. Epub 2019 May 23.

Department of Genetics, King Faisal Specialist Hospital and Research Centre, Riyadh 11211, Saudi Arabia; Saudi Human Genome Program, King Abdulaziz City for Science and Technology, Riyadh 12354, Saudi Arabia; College of Medicine, Alfaisal University, Riyadh 11533, Saudi Arabia. Electronic address:

We report the results of clinical exome sequencing (CES) on >2,200 previously unpublished Saudi families as a first-tier test. The predominance of autosomal-recessive causes allowed us to make several key observations. We highlight 155 genes that we propose to be recessive, disease-related candidates. We report additional mutational events in 64 previously reported candidates (40 recessive), and these events support their candidacy. We report recessive forms of genes that were previously associated only with dominant disorders and that have phenotypes ranging from consistent with to conspicuously distinct from the known dominant phenotypes. We also report homozygous loss-of-function events that can inform the genetics of complex diseases. We were also able to deduce the likely causal variant in most couples who presented after the loss of one or more children, but we lack samples from those children. Although a similar pattern of mostly recessive causes was observed in the prenatal setting, the higher proportion of loss-of-function events in these cases was notable. The allelic series presented by the wealth of recessive variants greatly expanded the phenotypic expression of the respective genes. We also make important observations about dominant disorders; these observations include the pattern of de novo variants, the identification of 74 candidate dominant, disease-related genes, and the potential confirmation of 21 previously reported candidates. Finally, we describe the influence of a predominantly autosomal-recessive landscape on the clinical utility of rapid sequencing (Flash Exome). Our cohort's genotypic and phenotypic data represent a unique resource that can contribute to improved variant interpretation through data sharing.
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http://dx.doi.org/10.1016/j.ajhg.2019.04.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6562004PMC
June 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

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

The oculoauriculofrontonasal syndrome: Further clinical characterization and additional evidence suggesting a nontraditional mode of inheritance.

Am J Med Genet A 2018 12 10;176(12):2740-2750. Epub 2018 Dec 10.

Centre de Génétique et Centre de Référence Anomalies du Développement et Syndromes Malformatifs de l'Interrégion Est, Centre Hospitalier Universitaire Dijon, Dijon, France.

The oculoauriculofrontonasal syndrome (OAFNS) is a rare disorder characterized by the association of frontonasal dysplasia (widely spaced eyes, facial cleft, and nose abnormalities) and oculo-auriculo-vertebral spectrum (OAVS)-associated features, such as preauricular ear tags, ear dysplasia, mandibular asymmetry, epibulbar dermoids, eyelid coloboma, and costovertebral anomalies. The etiology is unknown so far. This work aimed to identify molecular bases for the OAFNS. Among a cohort of 130 patients with frontonasal dysplasia, accurate phenotyping identified 18 individuals with OAFNS. We describe their clinical spectrum, including the report of new features (micro/anophtalmia, cataract, thyroid agenesis, polymicrogyria, olfactory bulb hypoplasia, and mandibular cleft), and emphasize the high frequency of nasal polyps in OAFNS (56%). We report the negative results of ALX1, ALX3, and ALX4 genes sequencing and next-generation sequencing strategy performed on blood-derived DNA from respectively, four and four individuals. Exome sequencing was performed in four individuals, genome sequencing in one patient with negative exome sequencing result. Based on the data from this series and the literature, diverse hypotheses can be raised regarding the etiology of OAFNS: mosaic mutation, epigenetic anomaly, oligogenism, or nongenetic cause. In conclusion, this series represents further clinical delineation work of the rare OAFNS, and paves the way toward the identification of the causing mechanism.
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http://dx.doi.org/10.1002/ajmg.a.40662DOI Listing
December 2018

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

Further delineation of the clinical spectrum of de novo TRIM8 truncating mutations.

Am J Med Genet A 2018 11 23;176(11):2470-2478. Epub 2018 Sep 23.

Génétique des Anomalies du Développement, UMR1231, Université de Bourgogne, Dijon, France.

De novo mutations of the TRIM8 gene, which codes for a tripartite motif protein, have been identified using whole exome sequencing (WES) in two patients with epileptic encephalopathy (EE), but these reports were not sufficient to conclude that TRIM8 was a novel gene responsible for EE. Here we report four additional patients presenting with EE and de novo truncating mutations of TRIM8 detected by WES, and give further details of the patient previously reported by the Epi4K consortium. Epilepsy of variable severity was diagnosed in children aged 2 months to 3.5 years of age. All patients had developmental delay of variable severity with no or very limited language, often associated with behavioral anomalies and unspecific facial features or MRI brain abnormalities. The phenotypic variability observed in these patients appeared related to the severity of the epilepsy. One patient presented pharmacoresistant EE with regression, recurrent infections and nephrotic syndrome, compatible with the brain and kidney expression of TRIM8. Interestingly, all mutations were located at the highly conserved C-terminus section of TRIM8. This collaborative study confirms that TRIM8 is a novel gene responsible for EE, possibly associated with nephrotic syndrome. This report brings new evidence on the pathogenicity of TRIM8 mutations and highlights the value of data-sharing to delineate the phenotypic characteristics and biological basis of extremely rare disorders.
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http://dx.doi.org/10.1002/ajmg.a.40357DOI Listing
November 2018

Autosomal-Recessive Mutations in AP3B2, Adaptor-Related Protein Complex 3 Beta 2 Subunit, Cause an Early-Onset Epileptic Encephalopathy with Optic Atrophy.

Am J Hum Genet 2016 Dec 23;99(6):1368-1376. Epub 2016 Nov 23.

Equipe d'Accueil 4271, Génétique des Anomalies du Développement, Université de Bourgogne, 21079 Dijon, France; INSERM 1141, Service de Neurologie Pédiatrique, Hôpital Robert Debré, 75019 Paris, France; Centre de Génétique et Centre de Référence Anomalies du Développement et Syndromes Malformatifs de l'Interrégion Est, Centre Hospitalier Universitaire Dijon, 21079 Dijon, France. Electronic address:

Early-onset epileptic encephalopathy (EOEE) represents a heterogeneous group of severe disorders characterized by seizures, interictal epileptiform activity with a disorganized electroencephalography background, developmental regression or retardation, and onset before 1 year of age. Among a cohort of 57 individuals with epileptic encephalopathy, we ascertained two unrelated affected individuals with EOEE associated with developmental impairment and autosomal-recessive variants in AP3B2 by means of whole-exome sequencing. The targeted sequencing of AP3B2 in 86 unrelated individuals with EOEE led to the identification of an additional family. We gathered five additional families with eight affected individuals through the Matchmaker Exchange initiative by matching autosomal-recessive mutations in AP3B2. Reverse phenotyping of 12 affected individuals from eight families revealed a homogeneous EOEE phenotype characterized by severe developmental delay, poor visual contact with optic atrophy, and postnatal microcephaly. No spasticity, albinism, or hematological symptoms were reported. AP3B2 encodes the neuron-specific subunit of the AP-3 complex. Autosomal-recessive variations of AP3B1, the ubiquitous isoform, cause Hermansky-Pudlak syndrome type 2. The only isoform for the δ subunit of the AP-3 complex is encoded by AP3D1. Autosomal-recessive mutations in AP3D1 cause a severe disorder cumulating the symptoms of the AP3B1 and AP3B2 defects.
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http://dx.doi.org/10.1016/j.ajhg.2016.10.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5142104PMC
December 2016

WDR73 Mutations Cause Infantile Neurodegeneration and Variable Glomerular Kidney Disease.

Hum Mutat 2015 Nov 6;36(11):1021-8. Epub 2015 Aug 6.

Institute of Human Genetics, University Hospital, Magdeburg, Germany.

Infantile-onset cerebellar atrophy (CA) is a clinically and genetically heterogeneous trait. Galloway-Mowat syndrome (GMS) is a rare autosomal recessive disease, characterized by microcephaly with brain anomalies including CA in some cases, intellectual disability, and early-infantile-onset nephrotic syndrome. Very recently, WDR73 deficiency was identified as the cause of GMS in five individuals. To evaluate the role of WDR73 mutations as a cause of GMS and other forms of syndromic CA, we performed Sanger or exome sequencing in 51 unrelated patients with CA and variable brain anomalies and in 40 unrelated patients with a diagnosis of GMS. We identified 10 patients from three CA and from two GMS families with WDR73 mutations including the original family described with CA, mental retardation, optic atrophy, and skin abnormalities (CAMOS). There were five novel mutations, of which two were truncating and three were missense mutations affecting highly conserved residues. Individuals carrying homozygous WDR73 mutations mainly presented with a pattern of neurological and neuroimaging findings as well as intellectual disability, while kidney involvement was variable. We document postnatal onset of CA, a retinopathy, basal ganglia degeneration, and short stature as novel features of WDR73-related disease, and define WDR73-related disease as a new entity of infantile neurodegeneration.
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http://dx.doi.org/10.1002/humu.22828DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4616260PMC
November 2015

PMPCA mutations cause abnormal mitochondrial protein processing in patients with non-progressive cerebellar ataxia.

Brain 2015 Jun 25;138(Pt 6):1505-17. Epub 2015 Mar 25.

1 Division of Clinical and Metabolic Genetics, The Hospital for Sick Children, University of Toronto, Toronto, ON, Canada 20 Division of Neurology, The Hospital for Sick Children, University of Toronto, Toronto, ON, Canada

Non-progressive cerebellar ataxias are a rare group of disorders that comprise approximately 10% of static infantile encephalopathies. We report the identification of mutations in PMPCA in 17 patients from four families affected with cerebellar ataxia, including the large Lebanese family previously described with autosomal recessive cerebellar ataxia and short stature of Norman type and localized to chromosome 9q34 (OMIM #213200). All patients present with non-progressive cerebellar ataxia, and the majority have intellectual disability of variable severity. PMPCA encodes α-MPP, the alpha subunit of mitochondrial processing peptidase, the primary enzyme responsible for the maturation of the vast majority of nuclear-encoded mitochondrial proteins, which is necessary for life at the cellular level. Analysis of lymphoblastoid cells and fibroblasts from patients homozygous for the PMPCA p.Ala377Thr mutation and carriers demonstrate that the mutation impacts both the level of the alpha subunit encoded by PMPCA and the function of mitochondrial processing peptidase. In particular, this mutation impacts the maturation process of frataxin, the protein which is depleted in Friedreich ataxia. This study represents the first time that defects in PMPCA and mitochondrial processing peptidase have been described in association with a disease phenotype in humans.
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http://dx.doi.org/10.1093/brain/awv057DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4542620PMC
June 2015

Targeted next-generation sequencing of a 12.5 Mb homozygous region reveals ANO10 mutations in patients with autosomal-recessive cerebellar ataxia.

Am J Hum Genet 2010 Dec 18;87(6):813-9. Epub 2010 Nov 18.

Department of Human Genetics, Radboud University Nijmegen Medical Centre, The Netherlands.

Autosomal-recessive cerebellar ataxias comprise a clinically and genetically heterogeneous group of neurodegenerative disorders. In contrast to their dominant counterparts, unraveling the molecular background of these ataxias has proven to be more complicated and the currently known mutations provide incomplete coverage for genotyping of patients. By combining SNP array-based linkage analysis and targeted resequencing of relevant sequences in the linkage interval with the use of next-generation sequencing technology, we identified a mutation in a gene and have shown its association with autosomal-recessive cerebellar ataxia. In a Dutch consanguineous family with three affected siblings a homozygous 12.5 Mb region on chromosome 3 was targeted by array-based sequence capture. Prioritization of all detected sequence variants led to four candidate genes, one of which contained a variant with a high base pair conservation score (phyloP score: 5.26). This variant was a leucine-to-arginine substitution in the DUF 590 domain of a 16K transmembrane protein, a putative calcium-activated chloride channel encoded by anoctamin 10 (ANO10). The analysis of ANO10 by Sanger sequencing revealed three additional mutations: a homozygous mutation (c.1150_1151del [p.Leu384fs]) in a Serbian family and a compound-heterozygous splice-site mutation (c.1476+1G>T) and a frameshift mutation (c.1604del [p.Leu535X]) in a French family. This illustrates the power of using initial homozygosity mapping with next-generation sequencing technology to identify genes involved in autosomal-recessive diseases. Moreover, identifying a putative calcium-dependent chloride channel involved in cerebellar ataxia adds another pathway to the list of pathophysiological mechanisms that may cause cerebellar ataxia.
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http://dx.doi.org/10.1016/j.ajhg.2010.10.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2997370PMC
December 2010

Rundataxin, a novel protein with RUN and diacylglycerol binding domains, is mutant in a new recessive ataxia.

Brain 2010 Aug;133(Pt 8):2439-47

Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/Université de Strasbourg, et Collège de France, 67404 Illkirch, France.

We have identified a novel form of recessive ataxia that segregates in three children of a large consanguineous Saudi Arabian family. The three patients presented with childhood onset gait and limb ataxia, dysarthria and had limited walking without aid into their teenage years. Two patients developed epilepsy at 7 months without relapse after treatment, and mental retardation. Linkage studies allowed us to identify a single locus that segregated with the disease on chromosome 3q28-qter. Mutation screening of all coding sequences revealed a single nucleotide deletion, 2927delC, in exon 19 of the KIAA0226 gene, which results in a frame shift of the C-terminal domain (p.Ala943ValfsX146). The KIAA0226 gene encodes a protein that we named rundataxin, with two conserved domains: an N-terminal RUN domain and a C-terminal domain containing a diacylglycerol binding-like motif. The closest paralogue of rundataxin, the plekstrin homology domain family member M1, has been shown to colocalize with Rab7, a small GTPase associated with late endosomes/lysosomes, suggesting that rundataxin may also be associated with vesicular trafficking and signalling pathways through its RUN and diacylglycerol binding-like domains. The rundataxin pathway appears therefore distinct from the ataxia pathways involving deficiency in mitochondrial or nuclear proteins and broadens the range of mechanisms leading to recessive ataxias.
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http://dx.doi.org/10.1093/brain/awq181DOI Listing
August 2010

Mutations in ABHD12 cause the neurodegenerative disease PHARC: An inborn error of endocannabinoid metabolism.

Am J Hum Genet 2010 Sep;87(3):410-7

Center for Medical Genetics and Molecular Medicine, Haukeland University Hospital, Bergen, Norway.

Polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataract (PHARC) is a neurodegenerative disease marked by early-onset cataract and hearing loss, retinitis pigmentosa, and involvement of both the central and peripheral nervous systems, including demyelinating sensorimotor polyneuropathy and cerebellar ataxia. Previously, we mapped this Refsum-like disorder to a 16 Mb region on chromosome 20. Here we report that mutations in the ABHD12 gene cause PHARC disease and we describe the clinical manifestations in a total of 19 patients from four different countries. The ABHD12 enzyme was recently shown to hydrolyze 2-arachidonoyl glycerol (2-AG), the main endocannabinoid lipid transmitter that acts on cannabinoid receptors CB1 and CB2. Our data therefore represent an example of an inherited disorder related to endocannabinoid metabolism. The endocannabinoid system is involved in a wide range of physiological processes including neurotransmission, mood, appetite, pain appreciation, addiction behavior, and inflammation, and several potential drugs targeting these pathways are in development for clinical applications. Our findings show that ABHD12 performs essential functions in both the central and peripheral nervous systems and the eye. Any future drug-mediated interference with this enzyme should consider the potential risk of long-term adverse effects.
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http://dx.doi.org/10.1016/j.ajhg.2010.08.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2933347PMC
September 2010

ADCK3, an ancestral kinase, is mutated in a form of recessive ataxia associated with coenzyme Q10 deficiency.

Am J Hum Genet 2008 Mar;82(3):661-72

Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/Université Louis Pasteur, et Collège de France, Chaire de génétique humaine, 67404 Illkirch, France.

Muscle coenzyme Q(10) (CoQ(10) or ubiquinone) deficiency has been identified in more than 20 patients with presumed autosomal-recessive ataxia. However, mutations in genes required for CoQ(10) biosynthetic pathway have been identified only in patients with infantile-onset multisystemic diseases or isolated nephropathy. Our SNP-based genome-wide scan in a large consanguineous family revealed a locus for autosomal-recessive ataxia at chromosome 1q41. The causative mutation is a homozygous splice-site mutation in the aarF-domain-containing kinase 3 gene (ADCK3). Five additional mutations in ADCK3 were found in three patients with sporadic ataxia, including one known to have CoQ(10) deficiency in muscle. All of the patients have childhood-onset cerebellar ataxia with slow progression, and three of six have mildly elevated lactate levels. ADCK3 is a mitochondrial protein homologous to the yeast COQ8 and the bacterial UbiB proteins, which are required for CoQ biosynthesis. Three out of four patients tested showed a low endogenous pool of CoQ(10) in their fibroblasts or lymphoblasts, and two out of three patients showed impaired ubiquinone synthesis, strongly suggesting that ADCK3 is also involved in CoQ(10) biosynthesis. The deleterious nature of the three identified missense changes was confirmed by the introduction of them at the corresponding positions of the yeast COQ8 gene. Finally, a phylogenetic analysis shows that ADCK3 belongs to the family of atypical kinases, which includes phosphoinositide and choline kinases, suggesting that ADCK3 plays an indirect regulatory role in ubiquinone biosynthesis possibly as part of a feedback loop that regulates ATP production.
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http://dx.doi.org/10.1016/j.ajhg.2007.12.024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2427193PMC
March 2008