Genetic underpinnings explored: OPA1 deletion and complex phenotypes on chromosome 3q29

BACKGROUND

Copy number variations (CNVs) have emerged as significant contributors to the elusive genetic causality of inherited eye diseases. In this study, we describe a case with optic atrophy and a brain aneurysm, in which a de novo CNV 3q29 deletion was identified.

CASE PRESENTATION

A 40-year-old female patient was referred to our department after undergoing aneurysm transcatheter arterial embolization for a brain aneurysm. She had no history of systemic diseases, except for unsatisfactory best-corrected visual acuity (BCVA) since elementary school. Electrophysiological tests confirmed the findings in retinal images, indicating optic nerve atrophy. Chromosomal microarray analysis revealed a de novo deletion spanning 960 kb on chromosome 3q29, encompassing OPA1 and six neighboring genes. Unlike previously reported deletions in this region associated with optic atrophy, neuropsychiatric disorders, and obesity, this patient displayed a unique combination of optic atrophy and a brain aneurysm. However, there is no causal relationship between the brain aneurysm and the CNV.

CONCLUSION

In conclusion, the optic atrophy is conclusively attributed to the OPA1 deletion, and the aneurysm could be a coincidental association. The report emphasizes the likelihood of underestimating OPA1 deletions due to sequencing technology limitations. Recognizing these constraints, healthcare professionals must acknowledge these limitations and consistently search for OPA1 variants/deletions in Autosomal Dominant Optic Atrophy (ADOA) patients with negative sequencing results. This strategic approach ensures a more comprehensive exploration of copy-number variations, ultimately enhancing diagnostic precision in the field of genetic disorders.

Recurrent MECR R258W causes adult-onset optic atrophy: A case report

MECR-related neurologic disorder, also known as mitochondrial enoyl CoA reductase protein-associated neurodegeneration (MEPAN) or dystonia with optic atrophy and basal ganglia abnormalities in childhood (MIM: #617282), is an autosomal recessive inherited disease characterized by a progressive childhood-onset movement disorder and optic atrophy. Here we report a 19-year-old male, presented with progressive visual failure, nystagmus, and right orbital pain, with no history of movement or eye disorder in his childhood. His visual decline started at age 18 years, whereas nystagmus emerged seven months later. Analysis of whole-exome sequencing (WES) revealed a homozygous recurrent variant (NM_016011.5:c.772C > T, p.Arg258Trp) in MECR. These findings suggest phenotypic heterogeneity in MECR-related neurologic disorder, thus, more relevant case screening, will help to delineate the genotype-phenotype correlation of the MECR gene.

Early Diagnosis of Wolfram Syndrome by Ophthalmologic Screening in a Patient with Type 1B Diabetes Mellitus: A Case Report

Wolfram syndrome (WS) is a monogenic diabetes caused by variants of the WFS1 gene. It is characterized by diabetes mellitus (DM) and optic atrophy. Individuals with WS initially present with autoantibody-negative type 1 DM (type 1B DM; T1BDM). The diagnosis is often delayed or misdiagnosed, even after visual impairment becomes apparent. We report a case of WS diagnosed by ophthalmologic screening before the appearance of visual impairment. A 7-year-old male patient developed T1BDM at the age of 3 years. At 6 years of age, his endogenous insulin secretion decreased but was not completely absent, and glycemic control was good with insulin treatment. Fundus examination at that time revealed optic nerve head pallor, and WFS1 gene analysis confirmed a compound heterozygous variant (c.2483delinsGGA/c.1247T>A). Ophthalmological screening can help in early diagnosis of WS in T1BDM, especially when endogenous insulin secretion is preserved, which would facilitate effective treatment.

Bi-allelic variants in SNF8 cause a disease spectrum ranging from severe developmental and epileptic encephalopathy to syndromic optic atrophy

The endosomal sorting complex required for transport (ESCRT) machinery is essential for membrane remodeling and autophagy and it comprises three multi-subunit complexes (ESCRT I-III). We report nine individuals from six families presenting with a spectrum of neurodevelopmental/neurodegenerative features caused by bi-allelic variants in SNF8 (GenBank: NM_007241.4), encoding the ESCRT-II subunit SNF8. The phenotypic spectrum included four individuals with severe developmental and epileptic encephalopathy, massive reduction of white matter, hypo-/aplasia of the corpus callosum, neurodevelopmental arrest, and early death. A second cohort shows a milder phenotype with intellectual disability, childhood-onset optic atrophy, or ataxia. All mildly affected individuals shared the same hypomorphic variant, c.304G>A (p.Val102Ile). In patient-derived fibroblasts, bi-allelic SNF8 variants cause loss of ESCRT-II subunits. Snf8 loss of function in zebrafish results in global developmental delay and altered embryo morphology, impaired optic nerve development, and reduced forebrain size. In vivo experiments corroborated the pathogenicity of the tested SNF8 variants and their variable impact on embryo development, validating the observed clinical heterogeneity. Taken together, we conclude that loss of ESCRT-II due to bi-allelic SNF8 variants is associated with a spectrum of neurodevelopmental/neurodegenerative phenotypes mediated likely via impairment of the autophagic flux.

Comprehensive overview of disease models for Wolfram syndrome: toward effective treatments

Wolfram syndrome (OMIM 222300) is a rare autosomal recessive disease with a devastating array of symptoms, including diabetes mellitus, optic nerve atrophy, diabetes insipidus, hearing loss, and neurological dysfunction. The discovery of the causative gene, WFS1, has propelled research on this disease. However, a comprehensive understanding of the function of WFS1 remains unknown, making the development of effective treatment a pressing challenge. To bridge these knowledge gaps, disease models for Wolfram syndrome are indispensable, and understanding the characteristics of each model is critical. This review will provide a summary of the current knowledge regarding WFS1 function and offer a comprehensive overview of established disease models for Wolfram syndrome, covering animal models such as mice, rats, flies, and zebrafish, along with induced pluripotent stem cell (iPSC)-derived human cellular models. These models replicate key aspects of Wolfram syndrome, contributing to a deeper understanding of its pathogenesis and providing a platform for discovering potential therapeutic approaches.

[Wolfram-like syndrome: a case report]

Different from classical autosomal recessive Wolfram syndrome, Wolfram-like syndrome is an autosomal dominant disorder caused by a heterozygous mutation in the WFS1 gene. In this case, a 7-year-old male child presented to the eye clinic due to vision loss that could not be corrected, discovered during a routine examination. The child had experienced hearing impairment since early childhood, leading to cochlear implantation. Ophthalmic examination revealed optic disc atrophy in both eyes. Optical coherence tomography imaging demonstrated a distinctive thickening of the outer plexiform layer with abnormal layering, characteristic of a single mutation in the WFS1 gene. Subsequent genetic testing identified a de novo heterozygous missense mutation c.2051C>T (p.A684V) in the WFS1 gene, which ultimately led to the diagnosis of Wolfram-like syndrome.

Refining the phenotypic spectrum of CCDC88A-related PEHO-like syndrome

Progressive encephalopathy with edema, hypsarrhythmia, and optic atrophy (PEHO) and PEHO-like syndromes are very rare infantile disorders characterized by profound intellectual disability, hypotonia, convulsions, optic, and progressive brain atrophy. Many causative genes for PEHO and PEHO-like syndromes have been identified including CCDC88A. So far, only five patients from two unrelated families with biallelic CCDC88A variants have been reported in the literature. Herein, we describe a new family from Egypt with a lethal epileptic encephalopathy. Our patient was the youngest child born to a highly consanguineous couple and had a family history of five deceased sibs with the same condition. She presented with postnatal microcephaly, poor visual responsiveness, and epilepsy. Her brain MRI showed abnormal cortical gyration with failure of opercularization of the insula, hypogenesis of corpus callosum, colpocephaly, reduced white matter, hypoplastic vermis, and brain stem. Whole exome sequencing identified a new homozygous frameshift variant in CCDC88A gene (c.1795_1798delACAA, p.Thr599ValfsTer4). Our study presents the third reported family with this extremely rare disorder. We also reviewed all described cases to better refine the phenotypic spectrum associated with biallelic loss of function variants in the CCDC88A gene.

Infantile epileptic spasm syndrome as a new NR2F1 gene phenotype

INTRODUCTION

NR2F1 pathogenetic variants are associated with the Bosch-Boonstra-Schaaf optic atrophy syndrome (BBSOAS). Recent studies indicate that BBSOAS patients not only have visual impairments but may also have developmental delays, hypotonia, thin corpus callosum and epileptic seizures. However, reports of BBSOAS occurrence along with infantile epileptic spasm syndrome (IESS) are rare.

METHODS

Here, we report three cases involving children with IESS and BBSOAS caused by de novo NR2F1 pathogenetic variants and summarize the genotype, clinical characteristics, diagnosis and treatment of them.

RESULTS

All three children experienced epileptic spasms and global developmental delays, with brain Magnetic Resonance Imaging (MRI) suggesting abnormalities (thinning of the corpus callosum or widened extracerebral spaces) and two of the children exhibiting abnormal visual evoked potentials.

CONCLUSIONS

Our findings indicate that new missense NR2F1 pathogenetic variants may lead to IESS with abnormal visual evoked potentials. Thus, clinicians should be aware of the Bosch-Boonstra-Schaaf optic atrophy syndrome and regular monitoring of the fundus, and the optic nerve is necessary during follow-up.

[Clinical features of CAPOS syndrome caused by maternal ATP1A3 gene variation: a case report]

CAPOS syndrome is an autosomal dominant neurological disorder caused by mutations in the ATP1A3 gene. Initial symptoms, often fever-induced, include recurrent acute ataxic encephalopathy in childhood, featuring cerebellar ataxia, optic atrophy, areflflexia, sensorineural hearing loss, and in some cases, pes cavus. This report details a case of CAPOS syndrome resulting from a maternal ATP1A3 gene mutation. Both the child and her mother exhibited symptoms post-febrile induction,including severe sensorineural hearing loss in both ears, ataxia, areflexia, and decreased vision. Additionally, the patient's mother presented with pes cavus. Genetic testing revealed a c. 2452G>A（Glu818Lys） heterozygous mutation in theATP1A3 gene in the patient . This article aims to enhance clinicians' understanding of CAPOS syndrome, emphasizing the case's clinical characteristics, diagnostic process, treatment, and its correlation with genotypeic findings.

A Homozygous NDUFS6 Variant Associated with Neuropathy and Optic Atrophy

Background

The NADH dehydrogenase [ubiquinone] iron-sulfur protein 6 (NDUFS6) gene encodes for an accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (complex I). Bi-allelic NDUFS6 variants have been linked with a severe disorder mostly reported as a lethal infantile mitochondrial disease (LMID) or Leigh syndrome (LS).

Objective

Here, we identified a homozygous variant (c.309 + 5 G > A) in NDUFS6 in one male patient with axonal neuropathy accompanied by loss of small fibers in skin biopsy and further complicated by optic atrophy and borderline intellectual disability.

Methods

To address the pathogenicity of the variant, biochemical studies (mtDNA copy number quantification, ELISA, Proteomic profiling) of patient-derived leukocytes were performed.

Results

The analyses revealed loss of NDUFS6 protein associated with a decrease of three further mitochondrial NADH dehydrogenase subunit/assembly proteins (NDUFA12, NDUFS4 and NDUFV1). Mitochondrial copy number is not altered in leukocytes and the mitochondrial biomarker GDF15 is not significantly changed in serum.

Conclusions

Hence, our combined clinical and biochemical data strengthen the concept of NDUFS6 being causative for a very rare form of axonal neuropathy associated with optic atrophy and borderline intellectual disability, and thus expand (i) the molecular genetic landscape of neuropathies and (ii) the clinical spectrum of NDUFS6-associated phenotypes.

Wolfram syndrome type 1: a case series

BACKGROUND

Wolfram syndrome (WS) is a rare autosomal recessive multisystem neurodegenerative disease characterized by non-autoimmune insulin-dependent diabetes mellitus, optic atrophy, sensorineural deafness, and diabetes as the main features. Owing to clinical phenotypic heterogeneity, the misdiagnosis rate is high. However, early accurate diagnosis and comprehensive management are key to improving quality of life and prolonging life.

RESULTS

Eleven patients from seven WS pedigrees with 10 mutation sites (c.1314_1317delCTTT, c.C529T, c.C529A, c.G2105A, c.C1885T, c.1859_1860del, c.G2020A, c.C529A, c.G2105A, and c.G1393C) in the WFS1 gene were included. We conducted further expert department analysis to clarify the diagnosis and analyze the correlation between genes and phenotypes.

CONCLUSIONS

The genotypes of these patients were closely associated with their phenotypes. The clinical data of the patients were analyzed to provide a basis for the diagnosis and clinical management of the disease.

[Analysis of NR2F1 gene variant in a child with optic atrophy and global developmental delay]

OBJECTIVE

To explore the genetic basis for a child with optic atrophy and global developmental delay.

METHODS

A child who had presented at the Guangzhou Women and Children's Medical Center in January 2022 was selected as the study subject. Clinical data were collected. Whole exome sequencing (WES) was carried out for the child. Candidate variant was validated by Sanger sequencing and bioinformatic analysis.

RESULTS

The child, a nine-month-old female, had manifested dysopia and global developmental delay. Genetic testing revealed that she has harbored a de novo c.425G>C (p.Arg142Pro) variant of the NR2F1 gene, which has been associated with Bosch-Boonstra-Schaaf syndrome. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), the variant was classified as pathogenic (PS2+PM1+PM2_Supporting+PM5+PP3+PP4).

CONCLUSION

The c.425G>C (p.Arg142Pro) variant of the NR2F1 gene probably underlay the pathogenesis in this child. Above finding has enriched the genotypic and phenotypic spectrum of the NR2F1 gene.

Variants in the WDR45 Gene Within the OPA-2 Locus Associate With Isolated X-Linked Optic Atrophy

Purpose

To describe clinical and molecular findings of two families with X-linked optic atrophy and present two new pathogenic variants in the WDR45 gene.

Methods

Case series and molecular analysis of two families of Jewish Ashkenazi descent with early onset bilateral optic atrophy. Whole-exome sequencing (WES) and bioinformatic analysis were performed, followed by Sanger sequencing and segregation analysis.

Results

In both families, male siblings (three in family 1, two in family 2) had early-onset isolated bilateral optic atrophy. The sibling's healthy mother (and in the second family also one healthy sister) had a mild presentation, suggesting a carrier state and an X-linked inheritance pattern. All participants were otherwise healthy, apart from mild learning disabilities and autism spectrum disorder in two siblings of the second family. Variants in known optic atrophy genes were excluded. Analysis revealed a point variant in the WDR45 gene-a missense variant in the first family, NM_001029896.2:c.107C>A; NP_001025067.1:p.Pro36His (variant ID: 1704205), and a splice site variant in the second family, NM_001029896.2:c.236-1G>T; NP_009006.2:p.Val80Leu (variant ID: 1704204), located on Xp11.23 (OPA2 locus). Both variants are novel and predicted as pathogenic. In both families, the variant was seen with full segregation with the disease, occurring in all affected male participants and in one allele of the carrier females, as well as none of the healthy participants.

Conclusions

Among two families with isolated X-linked optic atrophy, molecular analysis revealed novel variants in the WDR45 gene in full segregation with the disease. This gene resides within the OPA2 locus, previously described to associate with X-linked optic atrophy. Taken together, these findings suggest that certain pathogenic variants in the WDR45 gene are associated with isolated X-linked optic atrophy.

A new genetic cause of spastic ataxia: the p.Glu415Lys variant in TUBA4A

Tubulinopathies encompass neurodevelopmental disorders caused by mutations in genes encoding for different isotypes of α- and β-tubulins, the structural components of microtubules. Less frequently, mutations in tubulins may underlie neurodegenerative disorders. In the present study, we report two families, one with 11 affected individuals and the other with a single patient, carrying a novel, likely pathogenic, variant (p. Glu415Lys) in the TUBA4A gene (NM_006000). The phenotype, not previously described, is that of spastic ataxia. Our findings widen the phenotypic and genetic manifestations of TUBA4A variants and add a new type of spastic ataxia to be taken into consideration in the differential diagnosis.

Retinopathy and optic atrophy in a case of COQ2-related primary coenzyme Q10 deficiency

PURPOSE

To describe a case of primary coenzyme Q10 deficiency in a child manifesting as early-onset renal failure, retinal dystrophy, and optic atrophy leading to progressive vision loss.

METHODS

Clinical presentation and workup including visual fields, electroretinogram, and optical coherence tomography are presented. Genetic testing was performed.

RESULTS

An eight-year-old female with nephropathy requiring renal transplantation subsequently developed progressive cone-rod dystrophy and optic atrophy. The patient had negative results on a targeted next-generation sequencing retinal dystrophy panel but whole-exome sequencing revealed two variants in COQ2 (likely biallelic), consistent with a diagnosis of primary coenzyme Q10 deficiency.

CONCLUSIONS

Primary coenzyme Q10 deficiency is a rare disorder with variable systemic and ocular findings; there is also genetic heterogeneity. Genetic testing aids in the diagnosis of this condition, and variants in the COQ2 and PDSS1 genes appear to have the strongest association with ocular manifestations. Oral supplementation of coenzyme Q10 may slow progression of disease. This case highlights the utility of whole-exome sequencing in the diagnosis of a rare syndromic form of ocular disease and reports a novel phenotypic association for this condition.

Next generation sequencing identifies a pathogenic mutation of WFS1 gene in a Moroccan family with Wolfram syndrome: a case report

BACKGROUND

Wolfram syndrome is a rare autosomal recessive neurodegenerative disorder that affects 1/200,000 to 1/1,000,000 children. It is characterized by juvenile onset diabetes, optic nerve atrophy and other systemic manifestations. Symptoms of the disease arise mostly in early childhood with a high mortality rate due to severe neurological complications. Two causative genes have been identifed in this syndrome; the classical form is caused by autosomal recessive mutations of the WFS1 gene, and a smaller portion of patients has mutations in the CIDS2 gene, which are responsible for autosomal recessive Wolfram syndrome 2.

CASE PRESENTATION

We report the case of a 28-year-old Moroccan boy born from consanguineous parents referred to the department of medical genetics at the National Institute of Health in Rabat. The diagnosis of Wolfram syndrome was made based on insulin-dependent diabetes, optic nerve atrophy, sensorineural deafness, urological abnormalities and psychiatric illness. To establish the diagnosis at a molecular level, we performed next-generation sequencing in the index patient, which revealed compound heterozygous WFS1 mutations: c.1113G > A (p.Trp371Ter) and c.1223_1224insGGAACCACCTGGAGCCCTATGCCCATTT (p.Phe408fs). This second variant has never been described in patients with Wolfram syndrome.

CONCLUSION

The identification of the genetic substrate in our patient confirmed the clinical diagnosis of Wolfram syndrome and allowed us to provide him an appropriate management and genetic counseling to his family.

Genomics of Wolfram Syndrome 1 (WFS1)

Wolfram Syndrome (WFS) is a rare, autosomal, recessive neurogenetic disorder that affects many organ systems. It is characterised by diabetes insipidus, diabetes mellites, optic atrophy, and deafness and, therefore, is also known as DIDMOAD. Nearly 15,000-30,000 people are affected by WFS worldwide, and, on average, patients suffering from WFS die at 30 years of age, usually from central respiratory failure caused by massive brain atrophy. The more prevalent of the two kinds of WFS is WFS1, which is a monogenic disease and caused by the loss of the WFS1 gene, whereas WFS2, which is more uncommon, is caused by mutations in the CISD2 gene. Currently, there is no treatment for WFS1 to increase the life expectancy of patients, and the treatments available do not significantly improve their quality of life. Understanding the genetics and the molecular mechanisms of WFS1 is essential to finding a cure. The inability of conventional medications to treat WFS1 points to the need for innovative strategies that must address the fundamental cause: the deletion of the WFS1 gene that leads to the profound ER stress and disturbances in proteostasis. An important approach here is to understand the mechanism of the cell degeneration after the deletion of the WFS1 gene and to describe the differences in these mechanisms for the different tissues. The studies so far have indicated that remarkable clinical heterogeneity is caused by the variable vulnerability caused by WFS1 mutations, and these differences cannot be attributed solely to the positions of mutations in the WFS1 gene. The present review gives a broader overview of the results from genomic studies on the WFS1 mouse model.

A Diagnostic Approach to Spastic ataxia Syndromes

Spastic ataxia is characterized by the combination of cerebellar ataxia with spasticity and other pyramidal features. It is the hallmark of some hereditary ataxias, but it can also occur in some spastic paraplegias and acquired conditions. It often presents with heterogenous clinical features with other neurologic and non-neurological symptoms, resulting in complex phenotypes. In this review, the differential diagnosis of spastic ataxias are discussed and classified in accordance with inheritance. Establishing an organized classification method based on mode inheritance is fundamental for the approach to patients with these syndromes. For each differential, the clinical features, neuroimaging and genetic aspects are reviewed. A diagnostic approach for spastic ataxias is then proposed.

A fetus with Bosch-Boonstra-Schaaf optic atrophy syndrome characterized by bilateral ventricle widening: A case report and related literature review

RATIONALE

Bosch-Boonstra-Schaaf optic atrophy syndrome (BBSOAS) is a rare neurodevelopmental disorder caused by loss-of-function variants in the Nuclear Receptor Subfamily 2 Group F Member 1 (NR2F1). Here, we report a case of fetal BBSOAS. The fetus is typically featured by bilateral ventricle widening in the late second trimester, meanwhile, a 7.94-Mb deletion fragment on 5q14.3q15 involving the whole NR2F1 gene was confirmed by copy number variation sequencing (CNV-Seq) combined with karyotyping analysis. Our aim is to provide comprehensive prenatal clinical management strategy for fetal BBSOAS.

PATIENT CONCERNS

A 29-year-old primipara and her husband were referred to our prenatal diagnosis center due to the widening of bilateral ventricles at 29 + 1 weeks of gestation age.

DIAGNOSES

Ultrasound revealed the fetal widening posterior horns of bilateral ventricles at the GA of 27 + 3 weeks, 11 mm on the left and 10 mm on the right. At the following 29 + 1 weeks, ultrasound showed the posterior horn of the left lateral ventricle: 12 mm while the width of the right decreased to 9 mm, and intracranial arachnoid cyst. Furthermore, MRI confirmed that intracranial cyst might originate from an enlarged cisterna venae magnae cerebri, with mild dilation of 13.5 mm on the left ventricle. The fetal karyotyping analysis and CNV-Seq detection confirmed a 7.94-Mb deleted fragment on 5q14.3q15 (89340000_97280000) through the amniocentesis at 29 + 4 weeks of GA.

INTERVENTIONS

The fetus was closely monitored and underwent the following assessment by the multidisciplinary team.

OUTCOMES

The pregnancy was terminated in the end.

LESSONS

It is vital to use molecular and cytogenetical detections combined with a dynamic development history to make a definite diagnosis and evaluate the genetic status for the fetuses with BBSOAS.

A Novel Homozygous Founder Variant of RTN4IP1 in Two Consanguineous Saudi Families

The genetic architecture of mitochondrial disease continues to expand and currently exceeds more than 350 disease-causing genes. Bi-allelic variants in RTN4IP1, also known as Optic Atrophy-10 (OPA10), lead to early-onset recessive optic neuropathy, atrophy, and encephalopathy in the afflicted patients. The gene is known to encode a mitochondrial ubiquinol oxidoreductase that interacts with reticulon 4 and is thought to be a mitochondrial antioxidant NADPH oxidoreductase. Here, we describe two unrelated consanguineous families from the northern region of Saudi Arabia harboring a missense variant (RTN4IP1:NM_032730.5; c.475G Collapse

Key Words

• RTN4IP1
• age of variant
• encephalopathy
• founder variant
• in silico pathogenicity prediction
• missense
• optic atrophy
• structural modeling

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MESH Headings

• Antioxidants
• Brain Diseases
• Carrier Proteins/genetics
• Humans
• Mitochondrial Proteins/genetics
• Mutation/genetics
• NADP/genetics
• Optic Atrophy/genetics
• Oxidoreductases/genetics
• Saudi Arabia

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Grants

• MR/W019027/1 Medical Research Council
• MR/S005021/1 Medical Research Council
• Department of Health
• 203105/Z/16/Z Wellcome Trust
• G0800674 Medical Research Council

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Affiliation(s)

Mazhor Aldosary Translational Genomics Department, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Maysoon Alsagob Translational Genomics Department, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia Center of Excellence for Biomedicine, Joint Centers for Excellence Program, King Abdulaziz City for Science and Technology (KACST), Riyadh 11442, Saudi Arabia
Hanan AlQudairy Translational Genomics Department, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Ana C. González-Álvarez Bioscience Program, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia Computational Biology Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
Stefan T. Arold Bioscience Program, Biological and Environmental Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia Computational Biology Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia Centre de Biologie Structurale (CBS), INSERM, CNRS, Université de Montpellier, F-34090 Montpellier, France
Mohammad Anas Dababo Department of Pathology and Laboratory Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Omar A. Alharbi Radiology Department, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Rawan Almass Department of Medical Genomics, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
AlBandary AlBakheet Translational Genomics Department, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Dalia AlSarar Translational Genomics Department, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia Department of Botany and Microbiology, College of Science, King Saud University, Riyadh 11451, Saudi Arabia
Alya Qari Department of Medical Genomics, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Mysoon M. Al-Ansari Department of Botany and Microbiology, College of Science, King Saud University, Riyadh 11451, Saudi Arabia Department of Molecular Oncology, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Monika Oláhová Welcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
Saif A. Al-Shahrani Department of Medical Genomics, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Moeenaldeen AlSayed Department of Medical Genomics, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia College of Medicine, Alfaisal University, P.O. Box 50927, Riyadh 11533, Saudi Arabia
Dilek Colak Department of Molecular Oncology, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Robert W. Taylor Welcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne NE2 4HH, UK NHS Highly Specialized Service for Rare Mitochondrial Disorders, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne NE1 4LP, UK
Mohammed AlOwain Department of Medical Genomics, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia
Namik Kaya Translational Genomics Department, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Centre (KFSHRC), P.O. Box 3354, Riyadh 11211, Saudi Arabia

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Heterozygous UCHL1 loss-of-function variants cause a neurodegenerative disorder with spasticity, ataxia, neuropathy, and optic atrophy

PURPOSE

Biallelic variants in UCHL1 have been associated with a progressive early-onset neurodegenerative disorder, autosomal recessive spastic paraplegia type 79. In this study, we investigated heterozygous UCHL1 variants on the basis of results from cohort-based burden analyses.

METHODS

Gene-burden analyses were performed on exome and genome data of independent cohorts of patients with hereditary ataxia and spastic paraplegia from Germany and the United Kingdom in a total of 3169 patients and 33,141 controls. Clinical data of affected individuals and additional independent families were collected and evaluated. Patients' fibroblasts were used to perform mass spectrometry-based proteomics.

RESULTS

UCHL1 was prioritized in both independent cohorts as a candidate gene for an autosomal dominant disorder. We identified a total of 34 cases from 18 unrelated families, carrying 13 heterozygous loss-of-function variants (15 families) and an inframe insertion (3 families). Affected individuals mainly presented with spasticity (24/31), ataxia (28/31), neuropathy (11/21), and optic atrophy (9/17). The mass spectrometry-based proteomics showed approximately 50% reduction of UCHL1 expression in patients' fibroblasts.

CONCLUSION

Our bioinformatic analysis, in-depth clinical and genetic workup, and functional studies established haploinsufficiency of UCHL1 as a novel disease mechanism in spastic ataxia.

Characterization of a novel variant in the HR1 domain of MFN2 in a patient with ataxia, optic atrophy and sensorineural hearing loss

Background: Pathogenic variants in MFN2 cause Charcot-Marie-Tooth disease (CMT) type 2A (CMT2A) and are the leading cause of the axonal subtypes of CMT. CMT2A is characterized by predominantly distal motor weakness and muscle atrophy, with highly variable severity and onset age. Notably, some MFN2 variants can also lead to other phenotypes such as optic atrophy, hearing loss and lipodystrophy. Despite the clear link between MFN2 and CMT2A, our mechanistic understanding of how dysfunction of the MFN2 protein causes human disease pathologies remains incomplete. This lack of understanding is due in part to the multiple cellular roles of MFN2. Though initially characterized for its role in mediating mitochondrial fusion, MFN2 also plays important roles in mediating interactions between mitochondria and other organelles, such as the endoplasmic reticulum and lipid droplets. Additionally, MFN2 is also important for mitochondrial transport, mitochondrial autophagy, and has even been implicated in lipid transfer. Though over 100 pathogenic MFN2 variants have been described to date, only a few have been characterized functionally, and even then, often only for one or two functions. Method: Several MFN2-mediated functions were characterized in fibroblast cells from a patient presenting with cerebellar ataxia, deafness, blindness, and diffuse cerebral and cerebellar atrophy, who harbours a novel homozygous MFN2 variant, D414V, which is found in a region of the HR1 domain of MFN2 where few pathogenic variants occur. Results: We found evidence for impairment of several MFN2-mediated functions. Consistent with reduced mitochondrial fusion, patient fibroblasts exhibited more fragmented mitochondrial networks and had reduced mtDNA copy number. Additionally, patient fibroblasts had reduced oxygen consumption, fewer mitochondrial-ER contacts, and altered lipid droplets that displayed an unusual perinuclear distribution. Conclusion: Overall, this work characterizes D414V as a novel variant in MFN2 and expands the phenotypic presentation of MFN2 variants to include cerebellar ataxia.

Identification and analysis of deletion breakpoints in four Mohr-Tranebjærg syndrome (MTS) patients

Mohr-Tranebjærg syndrome is an X-linked syndrome characterized by sensorineural hearing impairment in childhood, followed by progressive neurodegeneration leading to a broad phenotypic spectrum. Genetically MTS is caused by pathogenic variants in the TIMM8A gene, including gene deletions and larger contiguous gene deletions. Some of the latter involve the neighboring gene BTK, resulting in agammaglobulinemia. By next-generation mate-pair sequencing we have mapped the chromosomal deletion breakpoints of one MTS case and three XLA-MTS cases and used breakpoint-spanning PCR to fine map the breakpoints by Sanger sequencing. Two of the XLA-MTS cases presented with large deletions (63.5 and 27.2 kb), and the junctional regions were characterized by long stretches of microhomology, indicating that the events have emerged through homologous recombination. Conversely, the MTS case exhibited a small 2 bp region of microhomology, and the regions were not characterized by extensive microhomology. The third XLA-MTS case had a more complex breakpoint, including a 59 bp inverted insertion, thus at least four breakpoints were involved in this event. In conclusion, mate-pair library generation combined with next-generation sequencing is an efficient method for breakpoint identification, also in regions characterized by repetitive elements.

Autosomal Recessive Spinocerebellar Ataxia Type 10: A Report of a New Case in Japan

Autosomal recessive spinocerebellar ataxia of type 10 (SCAR10) is a very rare neurodegenerative disease caused by mutations in the TMEM16K (ANO10) gene. This disorder is characterized by slowly progressive cerebellar ataxia and pyramidal signs inconstantly associated with cognitive decline, polyneuropathy, epilepsy, and vesicorectal dysfunction. To date, more than 40 cases have been reported in Europe. In contrast, only three cases have been identified in Asian countries. We herein report the third Japanese case of SCAR10 harboring a novel homozygous deletion mutation (c.616delG, p.Glu206Lysfs*17). This case presented with adult-onset slowly progressive spastic ataxia with cerebellar atrophy and mild cognitive decline.

Novel missense WFS1 variant causing autosomal dominant atypical Wolfram syndrome

BACKGROUND

In contrast to the classic autosomal recessive Wolfram syndrome, Wolfram-like syndrome (WLS) is an autosomal dominant disease caused by heterozygous variants in the WFS1 gene. Here, we present deep phenotyping of a mother and son with a WFS1 variant NM_006005.3:c.2508 G > T, p. (Lys836Asn) detected with next-generation sequencing, which is novel at the nucleotide level. In this Greek family, the proband and mother had sensorineural hearing loss and mild non-progressive vision loss with optic nerve atrophy. An initial optic atrophy panel that did not test for WFS1 was unremarkable, but a broader inherited retinal dystrophy panel found the WFS1 variant.

CONCLUSION

This study highlights the importance of including WFS1 sequencing in the evaluation of optic nerve atrophy to discover syndromic conditions.

An MFN2-related Charcot-Marie-Tooth Disease Patient with Optic Nerve Atrophy, Neurogenic Bladder Dysfunction, and Diaphragmatic Weakness

Charcot-Marie-Tooth disease (CMT) is a common hereditary peripheral polyneuropathy encompassing distinct monogenetic disorders. Pathogenic mutations in mitofusin 2 (MFN2) are the most frequent cause of its axonal type, CMT type 2A, with diverse phenotypes. We herein report a Japanese patient with a novel heterozygous MFN2 pathogenic variant (c.740 G>C, p.R247P) and severe CMT phenotypes, including progressive muscle weakness, optic atrophy, urinary inconsistency, and restrictive pulmonary dysfunction with eventration of the diaphragm that developed over her 60-year disease course. Our case expands the clinico-genetic features of MFN2-related CMT and highlights the need to evaluate infrequent manifestations during long-term care of CMT patients.

OUP accepted manuscript

Wolfram syndrome (WS) is a rare genetic disease characterized by diabetes, optic atrophy and deafness. Patients die at 35 years of age, mainly from respiratory failure or dysphagia. Unfortunately, there is no treatment to block the progression of symptoms and there is an urgent need for adequate research models. Here, we report on the phenotypical characterization of two loss-of-function zebrafish mutant lines: wfs1a^C825X and wfs1b^W493X. We observed that wfs1a deficiency altered the size of the ear and the retina of the fish. We also documented a decrease in the expression level of unfolded protein response (UPR) genes in basal condition and in stress condition, i.e. after tunicamycin treatment. Interestingly, both mutants lead to a decrease in their visual function measured behaviorally. These deficits were associated with a decrease in the expression level of UPR genes in basal and stress conditions. Interestingly, basal, ATP-linked and maximal mitochondrial respirations were transiently decreased in the wfs1b mutant. Taken together, these zebrafish lines highlight the critical role of wfs1a and wfs1b in UPR, mitochondrial function and visual physiology. These models will be useful tools to better understand the cellular function of Wfs1 and to develop novel therapeutic approaches for WS.

WFS1 protein expression correlates with clinical progression of optic atrophy in patients with Wolfram syndrome

BACKGROUND

Wolfram syndrome (WFS) is a rare disorder characterised by childhood-onset diabetes mellitus and progressive optic atrophy. Most patients have variants in the WFS1 gene. We undertook functional studies of WFS1 variants and correlated these with WFS1 protein expression and phenotype.

METHODS

9 patients with a clinical diagnosis of WFS were studied with quantitative PCR for markers of endoplasmic reticulum (ER) stress and immunoblotting of fibroblast protein extracts for WFS1 protein expression. Luciferase reporter assay was used to assess ATF-6 dependent unfolded protein response (UPR) activation.

RESULTS

6 patients with compound heterozygous nonsense mutations in WFS1 had no detectable WFS1 protein expression; 3 patients with missense variants had 4%, 45% and 48% WFS1 protein expression. One of these also had an OPA1 mutation and was reclassified as autosomal dominant optic atrophy-plus syndrome. There were no correlations between ER stress marker mRNA and WFS1 protein expression. ERSE-luciferase reporter indicated activation of the ATF6 branch of UPR in two patients tested. Patients with partial WFS1 expression showed milder visual acuity impairment (asymptomatic or colour blind only), compared with those with absent expression (registered severe vision impaired) (p=0.04). These differences remained after adjusting for duration of optic atrophy.

CONCLUSIONS

Patients with WFS who have partial WFS1 protein expression present with milder visual impairment. This suggests a protective effect of partial WFS1 protein expression on the severity and perhaps progression of vision impairment and that therapies to increase residual WFS1 protein expression may be beneficial.

SSBP1-Disease Update: Expanding the Genetic and Clinical Spectrum, Reporting Variable Penetrance and Confirming Recessive Inheritance

Purpose

To report novel genotypes and expand the phenotype spectrum of SSBP1-disease and explore potential disease mechanism.

Methods

Five families with previously unsolved optic atrophy and retinal dystrophy underwent whole genome sequencing as part of the National Institute for Health Research BioResource Rare-Diseases and the UK's 100,000 Genomes Project. In silico analysis and protein modelling was performed on the identified variants. Deep phenotyping including retinal imaging and International Society for Clinical Electrophysiology of Vision standard visual electrophysiology was performed.

Results

Seven individuals from five unrelated families with bilateral optic atrophy and/or retinal dystrophy with extraocular signs and symptoms in some are described. In total, 6 SSBP1 variants were identified including the previously unreported variants: c.151A>G, p.(Lys51Glu), c.335G>A p.(Gly112Glu), and c.380G>A, p.(Arg127Gln). One individual was found to carry biallelic variants (c.380G>A p.(Arg127Gln); c.394A>G p.(Ile132Val)) associated with likely autosomal recessive SSBP1-disease. In silico analysis predicted all variants to be pathogenic and Three-dimensional protein modelling suggested possible disease mechanisms via decreased single-stranded DNA binding affinity or impaired higher structure formation.

Conclusions

SSBP1 is essential for mitochondrial DNA replication and maintenance, with defects leading to a spectrum of disease that includes optic atrophy and/or retinal dystrophy, occurring with or without extraocular features. This study provides evidence of intrafamilial variability and confirms the existence of an autosomal recessive inheritance in SSBP1-disease consequent upon a previously unreported genotype.

ACO2 clinicobiological dataset with extensive phenotype ontology annotation

Pathogenic variants of the aconitase 2 gene (ACO2) are responsible for a broad clinical spectrum involving optic nerve degeneration, ranging from isolated optic neuropathy with recessive or dominant inheritance, to complex neurodegenerative syndromes with recessive transmission. We created the first public locus-specific database (LSDB) dedicated to ACO2 within the "Global Variome shared LOVD" using exclusively the Human Phenotype Ontology (HPO), a standard vocabulary for describing phenotypic abnormalities. All the variants and clinical cases listed in the literature were incorporated into the database, from which we produced a dataset. We followed a rational and comprehensive approach based on the HPO thesaurus, demonstrating that ACO2 patients should not be classified separately between isolated and syndromic cases. Our data highlight that certain syndromic patients do not have optic neuropathy and provide support for the classification of the recurrent pathogenic variants c.220C>G and c.336C>G as likely pathogenic. Overall, our data records demonstrate that the clinical spectrum of ACO2 should be considered as a continuum of symptoms and refines the classification of some common variants.

NDUFS3 depletion permits complex I maturation and reveals TMEM126A/OPA7 as an assembly factor binding the ND4-module intermediate

Complex I (CI) is the largest enzyme of the mitochondrial respiratory chain, and its defects are the main cause of mitochondrial disease. To understand the mechanisms regulating the extremely intricate biogenesis of this fundamental bioenergetic machine, we analyze the structural and functional consequences of the ablation of NDUFS3, a non-catalytic core subunit. We show that, in diverse mammalian cell types, a small amount of functional CI can still be detected in the complete absence of NDUFS3. In addition, we determine the dynamics of CI disassembly when the amount of NDUFS3 is gradually decreased. The process of degradation of the complex occurs in a hierarchical and modular fashion in which the ND4 module remains stable and bound to TMEM126A. We, thus, uncover the function of TMEM126A, the product of a disease gene causing recessive optic atrophy as a factor necessary for the correct assembly and function of CI.

A novel de novo heterozygous pathogenic variant in the SDHA gene results in childhood onset bilateral optic atrophy and cognitive impairment

Isolated defects in the mitochondrial respiratory chain complex II (CII; succinate-ubiquinone oxidoreductase) are extremely rare and mainly result from bi-allelic mutations in one of the nuclear encoded subunits: SDHA, SDHB and SDHD, which comprise CII and the assembly CII factor SDHAF1. We report an adolescent female who presented with global developmental delay, intellectual disability and childhood onset progressive bilateral optic atrophy. Whole exome sequencing of the patient and her unaffected parents identified the novel heterozygous de novo variant c.1984C > T [NM_004168.4] in the SDHA gene. Biochemical assessment of CII in the patient's derived fibroblasts and lymphocytes displayed considerably decreased CII residual activity compared with normal controls, when normalized to the integral mitochondrial enzyme citrate synthase. Protein modeling of the consequent p.Arg662Cys variant [NP-004159.2] suggested that this substitution will compromise the structural integrity of the FAD-binding protein at the C-terminus that will ultimately impair the FAD binding to SDHA, thus decreasing the entire CII activity. Our study emphasizes the role of certain heterozygous SDHA mutations in a distinct clinical phenotype dominated by optic atrophy and neurological impairment. This is the second mutation that has been reported to cause this phenotype. Furthermore, it adds developmental delay and cognitive disability to the expanding spectrum of the disorder. We propose to add SDHA to next generation sequencing gene panels of optic atrophy.

A novel mutation in RAB3GAP1 gene in Chinese patient causing the Warburg micro syndrome: A case report

RATIONALE

Warburg Micro syndrome is a rare, autosomal recessive disorder characterized by multiple organ abnormalities involving the ocular, nervous, and genital systems. This case report describes a novel mutation in the RAB3GAP1 gene associated with Warburg Micro syndrome.

PATIENT CONCERNS

A 6-month-old female infant with bilateral congenital cataracts and developmental delay was referred to our department for further assessment. She presented with facial dysmorphic features, including a prominent forehead, microphthalmia, wide nasal bridge, relatively narrow mouth, large anteverted ears, and micrognathia.

DIAGNOSES

The patient was diagnosed with Warburg Micro syndrome based on clinical manifestations, as well as a novel homozygous mutation in RAB3GAP1: c.75-2A>C. Both parents were identified as heterozygotic carriers of this mutation.

INTERVENTIONS

Bilateral cataract extraction and anterior vitrectomy were performed at age 6 months, followed by physical rehabilitation. Convex lenses were used to protect the eyes postoperatively until intraocular lens implantation.

OUTCOMES

Although the patient received physical rehabilitation, she suffered global developmental delay.

LESSONS

The c.75-2A>C mutation in RAB3GAP1 expands the spectrum of known mutations in this gene, and it may be associated with Warburg Micro syndrome. Genetic counselors may wish to take this finding into consideration, especially given the poor prognosis associated with the disease.

[Analysis of a case of Warburg micro syndrome type 1 due to variant of RAB3GAP1 gene]

OBJECTIVE

To explore the clinical and genetic characteristics of a child featuring developmental delay.

METHODS

The child was subjected to whole exome sequencing. Candidate variant was verified by Sanger sequencing.

RESULTS

Whole genome sequencing revealed that the child has carried compound heterozygous variants c.2607-1G>C and c.899 + 2dupT of the RAB3GAP1 gene, which were respectively derived from her mother and father.

CONCLUSION

A rare case of Warburg micro syndrome type 1 was diagnosed. The phenotype of the child was consistent with the literature, in addition with dysplasia of palatine arch, prominent high palatal arch and tooth dysplasia. Above finding has provided a basis for genetic counseling and prenatal diagnosis for the family.

Behr syndrome and hypertrophic cardiomyopathy in a family with a novel UCHL1 deletion

BACKGROUND

Behr syndrome is a clinically distinct, but genetically heterogeneous disorder characterized by optic atrophy, progressive spastic paraparesis, and motor neuropathy often associated with ataxia. The molecular diagnosis is based on gene panel testing or whole-exome/genome sequencing.

METHODS

Here, we report the clinical presentation of two siblings with a novel genetic form of Behr syndrome. We performed whole-exome sequencing in the two patients and their mother.

RESULTS

Both patients had a childhood-onset, slowly progressive disease resembling Behr syndrome, starting with visual impairment, followed by progressive spasticity, weakness, and atrophy of the lower legs and ataxia. They also developed scoliosis, leading to respiratory problems. In their late 30's, both siblings developed a hypertrophic cardiomyopathy and died of sudden cardiac death at age 43 and 40, respectively. Whole-exome sequencing identified the novel homozygous c.627_629del; p.(Gly210del) deletion in UCHL1.

CONCLUSIONS

The presentation of our patients raises the possibility that hypertrophic cardiomyopathy may be an additional feature of the clinical syndrome associated with UCHL1 mutations, and highlights the importance of cardiac follow-up and treatment in neurodegenerative disease associated with UCHL1 mutations.

Novel compound heterozygous ACO2 mutations in an infant with progressive encephalopathy: A newly identified neurometabolic syndrome

BACKGROUND

The ACO2 gene encodes mitochondrial aconitase, the enzyme involved in the second step of the tricarboxylic acid cycle, catalyzing the interconversion of citrate into isocitrate. To date, fewer than 20 families harboring ACO2 mutations have been identified since the first report of a neurodegenerative disorder such as infantile cerebellar retinal degeneration in 2012. Subsequently, various phenotypes, from isolated optic atrophy to spastic paraplegia, have been recognized. Here, we report a case of a newly identified neurometabolic syndrome resulting from novel ACO2 mutations, which expands the genetic spectrum and increases clinical awareness in real-world clinical practice.

CASE REPORT

A 2-month-old boy presented with hypotonia, cyanosis, and abnormal eye movements. He had severe psychomotor retardation and intractable seizures manifesting with cyanotic episodes. Diffuse cerebral atrophy and bilateral optic atrophy were noted without cerebellar atrophy. With unremarkable results on comprehensive diagnostic work-up and targeted genetic tests, whole exome sequencing revealed novel compound heterozygous variants in ACO2 (p.Met393Ile and p.Cys448Ser), which were confirmed by Sanger sequencing. Although no definitive signs suggestive of metabolic disturbances or mitochondrial dysfunction have been noted in patients with ACO2 mutations to date, elevated plasma glutamate levels were noted in our case.

CONCLUSION

A high index of clinical suspicion and awareness of this disease may aid in the diagnosis of cases with unknown neurodegenerative diseases, facilitated by deep sequencing.

Wolfram syndrome: clinical and genetic profiling of a cohort from a tertiary care centre with characterization of the primary gonadal failure

BACKGROUND

Wolfram syndrome (WFS) is a rare, monogenic neurodegenerative syndrome characterised by insulin requiring non-autoimmune diabetes mellitus (DM) and optic atrophy which are usually the earliest and commonest manifestations. However, there are other features which are under-recognized, adding to morbidity and premature mortality in these patients.

METHODS

Five patients (three males, two females) with genetically confirmed WFS at a single tertiary care centre were prospectively followed up. Their symptomatology, clinical profile, genetic analysis and radiology were analyzed. Multidisciplinary approach was used for comprehensive clinical care of this cohort. Patients with primary gonadal failure were subjected to biopsy and immunohistochemistry (IHC) for wolframin was performed.

RESULTS

DM was the earliest presenting manifestation at 6.2 ± 1.3 years followed by optic atrophy at 10.4 ± 2.3 years, diabetes insipidus at 12 ± 2.1 years and deafness at 12.8 ± 2.1 years. All patients were autoantibody negative with low C-peptide(<0.6 ng/ml). Hypoglycemic episodes were frequent (upto 60%) but there was no instance of diabetic ketoacidosis. Optic atrophy was present alongwith proliferative diabetic retinopathy and cataract in 40%. Uncommon manifestations included neuropsychiatric features, parasuicide, cystopathy, brainstem atrophy and hypergonadotropic hypogonadism only in adult males (n = 2). Testicular biopsy revealed partly hyalinised seminiferous tubules and prominence of Leydig cells. IHC confirmed the presence of mutated wolframin, which was not significantly different from normal testis specimen on protein quantification.

CONCLUSIONS

WFS requires a multidisciplinary approach with special emphasis on early diagnosis and management of other endocrine and non-endocrine features so as to improve long-term outcomes. Gonadal functions need periodic assessment, especially in adult males.

Recessive null-allele variants in MAG associated with spastic ataxia, nystagmus, neuropathy, and dystonia

INTRODUCTION

The gene encoding myelin-associated glycoprotein (MAG) has been implicated in autosomal-recessive spastic paraplegia type 75. To date, only four families with biallelic missense variants in MAG have been reported. The genotypic and phenotypic spectrum of MAG-associated disease awaits further elucidation.

METHODS

Four unrelated patients with complex neurologic conditions underwent whole-exome sequencing within research or diagnostic settings. Following determination of the underlying genetic defects, in-depth phenotyping and literature review were performed.

RESULTS

In all case subjects, we detected ultra-rare homozygous or compound heterozygous variants in MAG. The observed nonsense (c.693C > A [p.Tyr231*], c.980G > A [p.Trp327*], c.1126C > T [p.Gln376*], and 1522C > T [p.Arg508*]) and frameshift (c.517_521dupAGCTG [p.Trp174*]) alleles were predicted to result in premature termination of protein translation. Affected patients presented with variable combinations of psychomotor delay, ataxia, eye movement abnormalities, spasticity, dystonia, and neuropathic symptoms. Cerebellar signs, nystagmus, and pyramidal tract dysfunction emerged as unifying features in the majority of MAG-mutated individuals identified to date.

CONCLUSIONS

Our study is the first to describe biallelic null variants in MAG, confirming that loss of myelin-associated glycoprotein causes severe infancy-onset disease with central and peripheral nervous system involvement.

Warburg Micro Syndrome 1 due to Segmental Paternal Uniparental Isodisomy of Chromosome 2 Detected by Whole-Exome Sequencing and Homozygosity Mapping

Warburg micro syndrome (WARBM) is a rare autosomal recessive disorder characterized by microcephaly, cortical dysplasia, intellectual disability, ocular abnormalities, spastic diplegia, and microgenitalia. WARBM has 4 subtypes arising from pathogenic variants in 4 genes (RAB18, RAB3GAP1, RAB3GAP2, and TBC1D20). Here, we report on a patient with a homozygous pathogenic c.665delC (p.Pro222HisfsTer30) variant in the RAB3GAP1 gene identified by whole-exome sequencing (WES) analyses. Only his father was a heterozygous carrier, and homozygosity mapping analysis of the WES data revealed large loss-of-heterozygosity regions in both arms of chromosome 2, interpreted as uniparental isodisomy. This uniparental disomy pattern could be due to paternal meiosis I nondisjunction because of the preserved heterozygosity in the pericentromeric region. This report provides novel insights, including a rare form of UPD, usage of homozygosity mapping analysis for the evaluation of isodisomy, and the first reported case of WARBM1 as a result of uniparental isodisomy.

Recessive ACO2 variants as a cause of isolated ophthalmologic phenotypes

The mitochondrial aconitase gene (ACO2) encodes an enzyme that catalyzes the conversion of citrate to isocitrate in the tricarboxylic acid cycle. Biallelic variants in ACO2 are purported to cause two distinct disorders: infantile cerebellar-retinal degeneration (ICRD) which is characterized by CNS abnormalities, neurodevelopmental phenotypes, optic atrophy and retinal degeneration; and optic atrophy 9 (OPA9), characterized by isolated ophthalmologic phenotypes including optic atrophy and low vision. However, some doubt remains as to whether biallelic ACO2 variants can cause isolated ophthalmologic phenotypes. A review of the literature revealed five individuals from three families who carry biallelic ACO2 variants whose phenotypes are consistent with OPA9. Here, we describe a brother and sister with OPA9 who are compound heterozygous for novel missense variants in ACO2; c.[487G>T];[1894G>A], p.[(Val163Leu)];[(Val632Met)]. A review of pathogenic ACO2 variants revealed that those associated with OPA9 are distinct from those associated with ICRD. Missense variants associated with either OPA9 or ICRD do not cluster in distinct ACO2 domains, making it difficult to predict the severity of a variant based on position alone. We conclude that biallelic variants in ACO2 can cause the milder OPA9 phenotype, and that the OPA9-related ACO2 variants identified to date are distinct from those that cause ICRD.

Martsolf syndrome with novel mutation in the TBC1D20 gene in a family from Iran

Warburg Micro syndrome and Martsolf syndrome are phenotypically overlapping autosomal recessive conditions characterized by multiple organ abnormalities involving the ocular, nervous, and endocrine systems. Warburg Micro syndrome, the more severe of the two conditions, is caused by loss of function mutations in RAB3GAP1, RAB3GAP2, RAB18, and TBC1D20 genes, whereas Martsolf syndrome has been attributed to less damaging mutations in RAB3GAP1 and RAB3GAP2 genes. We report the clinical description and molecular characterization of a consanguineous Iranian family with two siblings, a male and a female, with dysmorphic features, bilateral congenital cataracts, optic nerve atrophy, congenital glaucoma, mild to moderate intellectual disability, seizures, hypogonadism, and mild osteoporosis. Spastic quadriplegia with contractures was observed in the male patient, while the female patient showed only mild hyperreflexia. Magnetic resonance imaging scans performed in the male patient showed a normal brain structure. Both siblings had neither microcephaly nor postnatal growth retardation. Whole exome sequencing identified a novel homozygous nonsense mutation [c.1060C>T; p.(Arg354Ter)] in the TBC1D20 gene in both siblings and confirmed the heterozygous carrier status of both parents. This report describes a novel mutation in the TBC1D20 gene in two Iranian patients with Martsolf syndrome, further extending the allelic heterogeneity and phenotypic spectrum of this rare condition. The genotype and phenotype of the patients are compared with those of Martsolf syndrome and Warburg Micro syndrome patients reported in the literature.

Segregation of two variants suggests the presence of autosomal dominant and recessive forms of WFS1-related disease within the same family: expanding the phenotypic spectrum of Wolfram Syndrome

BACKGROUND

WFS1 was initially described as causative agent of autosomal recessive (AR) Wolfram syndrome, a childhood-onset disorder involving diabetes, optic atrophy, hearing loss and neurodegenerative features. However, the discovery of autosomal dominant (AD) disorders caused by this gene has resulted in clinical counselling and result interpretation challenges.

OBJECTIVE

We seek to report a family that appears to segregate dominant and recessive forms of WFS1-related disease.

METHODS/RESULTS

A 19-year-old woman presented with progressive childhood sensorineural hearing loss and recent optic atrophy, with biallelic mutations in WFS1: c.2486T>C (likely pathogenic) and c.2470G>A (uncertain significance). Her A1C was normal. Her sister carried the same variants and had a similar phenotype. Their father carried c.2486T>C and was found to have mild-moderate hearing loss but no optic atrophy or neurological symptoms. The mother carried c.2470G>A and had a normal audiogram and ophthalmological exam. Providing anticipatory guidance for this family was difficult given the phenotypic variability of WFS1-related disorders and the uncertainty surrounding whether the inheritance pattern was AR or AD.

CONCLUSION

The clinical correlation of the variants identified in this family suggests an AR Wolfram-like syndrome, without the typical diabetes mellitus or diabetes insipidus nor neurological decline. To our knowledge, this is a novel WFS1-related phenotype.

Hereditary Myelopathies

PURPOSE OF REVIEW

Hereditary myelopathies are very diverse genetic disorders, and many of them represent a widespread neurodegenerative process rather than isolated spinal cord dysfunction. This article reviews various types of inherited myelopathies, with emphasis on hereditary spastic paraplegias and spastic ataxias.

RECENT FINDINGS

The ever-growing number of myelopathy-causing genes and broadening of phenotype-genotype correlations makes the molecular diagnosis of inherited myelopathies a daunting task. This article emphasizes the main phenotypic clusters among inherited myelopathies that can facilitate the diagnostic process. This article focuses on newly identified genetic causes and the most important identifying clinical features that can aid the diagnosis, including the presence of a characteristic age of onset and additional neurologic signs such as leukodystrophy, thin corpus callosum, or amyotrophy.

SUMMARY

The exclusion of potentially treatable causes of myelopathy remains the most important diagnostic step. Syndromic diagnosis can be supported by molecular diagnosis, but the genetic diagnosis at present does not change the management. Moreover, a negative genetic test does not exclude the diagnosis of a hereditary myelopathy because comprehensive molecular testing is not yet available, and many disease-causing genes remain unknown.

A Sporadic Case of Charcot-Marie-Tooth Disease Type 2 with Left Vocal Fold Palsy due to Mitofusin 2 Mutation

A 33-year-old Japanese woman was referred for hoarseness. She had been diagnosed with Charcot-Marie-Tooth disease at age 3 and bilateral optic atrophy at age 15. Laryngoscopy revealed left vocal fold palsy. These findings suggested Charcot-Marie-Tooth disease type 2; the diagnosis was confirmed by a mitofusin 2 mutation analysis. Her symptoms remained stable for almost 10 years. Although vocal fold palsy and optic atrophy have been previously reported in patients with mitofusin 2 mutations, detailed clinical information and clinical course have never been documented. These data might contribute to the elucidation of the pathological conditions associated with mitofusin 2 mutations.