Identification of a Novel Mutation in the Titin Gene in a Chinese Family with Limb-Girdle Muscular Dystrophy 2J

Titinopathies: Phenotype - genotype heterogeneity in an Indian cohort

INTRODUCTION

Titinopathies are heterogenous group of disorders affecting the skeletal and cardiac muscles variably and caused by Titin (TTN) gene mutations located in Chromosome 2. The manifestations extend from congenital to adult-onset myopathies. Here we describe the phenotype-genotype heterogeneity of patients with myopathy/muscular dystrophy associated with TTN variants in an Indian cohort.

METHODS

A retrospective descriptive study of 12 patients diagnosed with primary muscle disease evaluated between 2016 and 2023 harboring rare TTN variants.

RESULTS

Eight patients were included (M:F ratio - 3:1). The median age at onset of entire cohort is 5 (range: birth- 33 years). The major clinical phenotypes were congenital myopathy [n = 3, 37.5%], juvenile onset myopathy [n = 3, 37.5%] and adult AD - Hereditary myopathy with early respiratory failure (HMERF) phenotype [n = 2, P6, P8; 25%]. Prominent / wide first interdigital space in feet in congenital and juvenile forms (c.38421_38437delinsC, c.106531 + 1G > A) was a novel feature. The variant c.95134T > C previously reported in HMERF in British population, was noted in two patients in our cohort and with GNE myopathy like phenotype in one. Muscle MRI done in congenital myopathy (c.26201-1G > A) showed fatty infiltration of anterior and posterior thigh with sparing of gracilis, adductor magnus and tibialis anterior.

CONCLUSION

This is the first Indian study with a large cohort demonstrating many novel mutations and clinical heterogeneity expanding the spectrum of titinopathies.

SpliceTransformer predicts tissue-specific splicing linked to human diseases

We present SpliceTransformer (SpTransformer), a deep-learning framework that predicts tissue-specific RNA splicing alterations linked to human diseases based on genomic sequence. SpTransformer outperforms all previous methods on splicing prediction. Application to approximately 1.3 million genetic variants in the ClinVar database reveals that splicing alterations account for 60% of intronic and synonymous pathogenic mutations, and occur at different frequencies across tissue types. Importantly, tissue-specific splicing alterations match their clinical manifestations independent of gene expression variation. We validate the enrichment in three brain disease datasets involving over 164,000 individuals. Additionally, we identify single nucleotide variations that cause brain-specific splicing alterations, and find disease-associated genes harboring these single nucleotide variations with distinct expression patterns involved in diverse biological processes. Finally, SpTransformer analysis of whole exon sequencing data from blood samples of patients with diabetic nephropathy predicts kidney-specific RNA splicing alterations with 83% accuracy, demonstrating the potential to infer disease-causing tissue-specific splicing events. SpTransformer provides a powerful tool to guide biological and clinical interpretations of human diseases.

Digenic inheritance involving a muscle-specific protein kinase and the giant titin protein causes a skeletal muscle myopathy

In digenic inheritance, pathogenic variants in two genes must be inherited together to cause disease. Only very few examples of digenic inheritance have been described in the neuromuscular disease field. Here we show that predicted deleterious variants in SRPK3, encoding the X-linked serine/argenine protein kinase 3, lead to a progressive early onset skeletal muscle myopathy only when in combination with heterozygous variants in the TTN gene. The co-occurrence of predicted deleterious SRPK3/TTN variants was not seen among 76,702 healthy male individuals, and statistical modeling strongly supported digenic inheritance as the best-fitting model. Furthermore, double-mutant zebrafish (srpk3-/-; ttn.1+/-) replicated the myopathic phenotype and showed myofibrillar disorganization. Transcriptome data suggest that the interaction of srpk3 and ttn.1 in zebrafish occurs at a post-transcriptional level. We propose that digenic inheritance of deleterious changes impacting both the protein kinase SRPK3 and the giant muscle protein titin causes a skeletal myopathy and might serve as a model for other genetic diseases.

Walking with giants: The challenges of variant impact assessment in the giant sarcomeric protein titin

Titin, the so-called "third filament" of the sarcomere, represents a difficult challenge for the determination of damaging genetic variants. A single titin molecule extends across half the length of a sarcomere in striated muscle, fulfilling a variety of vital structural and signaling roles, and has been linked to an equally varied range of myopathies, resulting in a significant burden on individuals and healthcare systems alike. While the consequences of truncating variants of titin are well-documented, the ramifications of the missense variants prevalent in the general population are less so. We here present a compendium of titin missense variants-those that result in a single amino-acid substitution in coding regions-reported to be pathogenic and discuss these in light of the nature of titin and the variant position within the sarcomere and their domain, the structural, pathological, and biophysical characteristics that define them, and the methods used for characterization. Finally, we discuss the current knowledge and integration of the multiple fields that have contributed to our understanding of titin-related pathology and offer suggestions as to how these concurrent methodologies may aid the further development in our understanding of titin and hopefully extend to other, less well-studied giant proteins. This article is categorized under: Cardiovascular Diseases > Genetics/Genomics/Epigenetics Congenital Diseases > Genetics/Genomics/Epigenetics Congenital Diseases > Molecular and Cellular Physiology.

Novel MFSD8 Variants in a Chinese Family with Nonsyndromic Macular Dystrophy

Purpose

To identify the molecular etiology of a Chinese family with nonsyndromic macular dystrophy.

Methods

Ophthalmic examinations were performed, and genomic DNA was extracted from available family members. Whole exome sequencing of two members (the proband and her unaffected mother) and Sanger sequencing in available family members were performed to screen potential pathogenic variants.

Results

Novel compound heterozygous variants, c.1066C>T (p.Pro356Ser) and c.1102+2T>C, in the major facilitator superfamily domain containing 8 gene (MFSD8) were suspected to be involved in this family's macular dystrophy phenotype. The novel c.1066C>T variant in the MFSD8 gene probably resulted in substitution of serine for proline at the 356th residue and was predicted to be “uncertain significance” through in silico analyses. The novel c.1102+2T>C variant in the MFSD8 gene was likely to affect the splicing form and predicted to be “pathogenic.”

Conclusion

The novel compound heterozygous variants, c.1066C>T (p.Pro356Ser) and c.1102+2T>C, in the MFSD8 gene are likely responsible for the isolated macular dystrophy phenotype in this family. This study enlarged the MFSD8 gene mutant spectrum and might provide more accurate genetic counseling for this family.

Building a Chinese pan-genome of 486 individuals

Pan-genome sequence analysis of human population ancestry is critical for expanding and better defining human genome sequence diversity. However, the amount of genetic variation still missing from current human reference sequences is still unknown. Here, we used 486 deep-sequenced Han Chinese genomes to identify 276 Mbp of DNA sequences that, to our knowledge, are absent in the current human reference. We classified these sequences into individual-specific and common sequences, and propose that the common sequence size is uncapped with a growing population. The 46.646 Mbp common sequences obtained from the 486 individuals improved the accuracy of variant calling and mapping rate when added to the reference genome. We also analyzed the genomic positions of these common sequences and found that they came from genomic regions characterized by high mutation rate and low pathogenicity. Our study authenticates the Chinese pan-genome as representative of DNA sequences specific to the Han Chinese population missing from the GRCh38 reference genome and establishes the newly defined common sequences as candidates to supplement the current human reference.

Identification of compound heterozygous DNAH11 variants in a Han-Chinese family with primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) is a group of genetically and clinically heterogeneous disorders with motile cilia dysfunction. It is clinically characterized by oto‐sino‐pulmonary diseases and subfertility, and half of the patients have situs inversus (Kartagener syndrome). To identify the genetic cause in a Han‐Chinese pedigree, whole‐exome sequencing was conducted in the 37‐year‐old proband, and then, Sanger sequencing was performed on available family members. Minigene splicing assay was applied to verify the impact of the splice‐site variant. Compound heterozygous variants including a splice‐site variant (c.1974‐1G>C, rs1359107415) and a missense variant (c.7787G>A, p.(Arg2596Gln), rs780492669), in the dynein axonemal heavy chain 11 gene (DNAH11) were identified and confirmed as the disease‐associated variants of this lineage. The minigene expression in vitro revealed that the c.1974‐1G>C variant could cause skipping over exon 12, predicted to result in a truncated protein. This discovery may enlarge the DNAH11 variant spectrum of PCD, promote accurate genetic counselling and contribute to PCD diagnosis.

The Sarcomeric Spring Protein Titin: Biophysical Properties, Molecular Mechanisms, and Genetic Mutations Associated with Heart Failure and Cardiomyopathy

PURPOSE OF REVIEW

The giant protein titin forms the "elastic" filament of the sarcomere, essential for the mechanical compliance of the heart muscle. Titin serves a biological spring, and therefore structural modifications of titin affect function of the myocardium and are associated with heart failure and cardiomyopathy.

RECENT FINDINGS

In this review, we discuss the current understanding of titin's biophysical properties and how modifications contribute to cardiac function and heart failure. In addition, we review the most recent data on the clinical impact and phenotype heterogeneity of TTN truncating variants, including diseases involving striated muscles, and prospects for future therapies. Because of the giant structure of the titin protein and the complexity of its function, titin's role in health and disease is not yet completely understood. Future research efforts need to focus on novel therapeutic approaches able to modulate titin transcriptional and post-translational modification.

The constantly evolving spectrum of phenotypes in titinopathies - will it ever stop?

PURPOSE OF REVIEW

The last few years have confirmed previous assumptions of an enormous impact of the titin gene (TTN) on the occurrence of muscle disease, cardiomyopathy, or both together. The reason for this rather late understanding of its importance is because of the huge size which prevented sequencing of the whole gene by the previous Sanger technique in the individual cases. An update of the advances in diagnosing titinopathies is the main focus of this review.

RECENT FINDINGS

High throughput methods are now widely available for TTN sequencing and a corresponding explosion of different types of identified titinopathies is observed and published in the literature, although final confirmation is lacking in many cases with recessive missense variants.

SUMMARY

The implications of these findings for clinical practice are easy to understand: patients with previously undiagnosed muscle disease can now have a correct diagnosis and subsequently receive a likely prognosis, can have accurate genetic counseling for the whole family and early treatment for predictable complications from the heart and respiratory muscles. In addition not to forget, they can avoid wrong diagnoses leading to wrong treatments.

Digenic Variants in the TTN and TRAPPC11 Genes Co-segregating With a Limb-Girdle Muscular Dystrophy in a Han Chinese Family

Limb-girdle muscular dystrophies (LGMD) are hereditary genetic disorders characterized by progressive muscle impairment which predominantly include proximal muscle weaknesses in the pelvic and shoulder girdles. This article describes an attempt to identify genetic cause(s) for a LGMD pedigree via a combination of whole exome sequencing and Sanger sequencing. Digenic variants, the titin gene (TTN) c.19481T>G (p.Leu6494Arg) and the trafficking protein particle complex 11 gene (TRAPPC11) c.3092C>G (p.Pro1031Arg), co-segregated with the disease phenotype in the family, suggesting their possible pathogenicity.

How wide is the application of genetic big data in biomedicine

In the era of big data, massive genetic data, as a new industry, has quickly swept almost all industries, especially the pharmaceutical industry. As countries around the world start to build their own gene banks, scientists study the data to explore the origins and migration of humans. Moreover, big data encourage the development of cancer therapy and bring good news to cancer patients. Big datum has been involved in the study of many diseases, and it has been found that analyzing diseases at the gene level can lead to more beneficial treatment options than ordinary treatments. This review will introduce the development of extensive data in medical research from the perspective of big data and tumor, neurological and psychiatric diseases, cardiovascular diseases, other applications and the development direction of big data in medicine.

Expanding the Clinico-Genetic Spectrum of Myofibrillar Myopathy: Experience From a Chinese Neuromuscular Center

Background: Myofibrillar myopathy is a group of hereditary neuromuscular disorders characterized by dissolution of myofibrils and abnormal intracellular accumulation of Z disc-related proteins. We aimed to characterize the clinical, physiological, pathohistological, and genetic features of Chinese myofibrillar myopathy patients from a single neuromuscular center.

Methods: A total of 18 patients were enrolled. Demographic and clinical data were collected. Laboratory investigations, electromyography, and cardiac evaluation was performed. Routine and immunohistochemistry stainings against desmin, αB-crystallin, and BAG3 of muscle specimen were carried out. Finally, next-generation sequencing panel array for genes associated with hereditary neuromuscular disorders were performed.

Results: Twelve pathogenic variants in DES, BAG3, FLNC, FHL1, and TTN were identified, of which seven were novel mutations. The novel DES c.1256C>T substitution is a high frequency mutation. The combined recessively/dominantly transmitted c.19993G>T and c.107545delG mutations in TTN gene cause a limb girdle muscular dystrophy phenotype with the classical myofibrillar myopathy histological changes.

Conclusions: We report for the first time that hereditary myopathy with early respiratory failure patient can have peripheral nerve and severe spine involvement. The mutation in Ig-like domain 16 of FLNC is associated with the limb girdle type of filaminopathy, and the mutation in Ig-like domain 18 with distal myopathy type. These findings expand the phenotypic and genotypic correlation spectrum of myofibrillar myopathy.

Genetics of Muscle Stiffness, Muscle Elasticity and Explosive Strength

Muscle stiffness, muscle elasticity and explosive strength are the main components of athletes' performance and they show a sex-based as well as ethnicity variation. Muscle stiffness is thought to be one of the risk factors associated with sports injuries and is less common in females than in males. These observations may be explained by circulating levels of sex hormones and their specific receptors. It has been shown that higher levels of estrogen are associated with lower muscle stiffness responsible for suppression of collagen synthesis. It is thought that these properties, at least in part, depend on genetic factors. Particularly, the gene encoding estrogen receptor 1 (ESR1) is one of the candidates that may be associated with muscle stiffness. Muscle elasticity increases with aging and there is evidence suggesting that titin (encoded by the TTN gene), a protein that is expressed in cardiac and skeletal muscles, is one of the factors responsible for elastic properties of the muscles. Mutations in the TTN gene result in some types of muscular dystrophy or cardiomyopathy. In this context, TTN may be regarded as a promising candidate for studying the elastic properties of muscles in athletes. The physiological background of explosive strength depends not only on the muscle architecture and muscle fiber composition, but also on the central nervous system and functionality of neuromuscular units. These properties are, at least partly, genetically determined. In this context, the ACTN3 gene code for α-actinin 3 has been widely researched.

Novel GLI3 Mutations in Chinese Patients with Non-syndromic Post-axial Polydactyly

BACKGROUND

Polydactyly, characterized by supernumerary digits in the upper or lower extremities, is the most common congenital digital abnormalities. It derives from the defective patterning of anteroposterior axis of the developing limb, with various etiology and clinical heterogeneity. The patients with post-axial polydactyly type A (PAPA) have the typical symptom of a well-formed supernumerary digit outside the fifth digit.

OBJECTIVE

The aim of present study was to identify the causative mutations of two unrelated Han Chinese patients with non-syndromic PAPA.

METHODS

Two unrelated Han Chinese patients and 100 ethnicity-matched, unrelated normal controls were recruited for this study. BGISEQ-500 exome sequencing was performed in the two patients, followed by validation in the patients and 100 controls by using Sanger sequencing.

RESULTS

Two mutations in the GLI family zinc finger 3 gene (GLI3), including a frameshift mutation c.3437_3453delTCGAGCAGCCCTGCCCC (p.L1146RfsX95) and a nonsense mutation c.3997C>T (p.Q1333X), were identified in two patients but were absent in the 100 healthy controls.

CONCLUSION

The two GLI3 mutations, p.L1146RfsX95 and p.Q1333X, may account for non-syndromic PAPA in the two patients, respectively. The findings of this study may expand the mutational spectrum of GLI3-PAPA and provide novel insights into the genetic basis of polydactyly.

Structural diversity in the atomic resolution 3D fingerprint of the titin M-band segment

In striated muscles, molecular filaments are largely composed of long protein chains with extensive arrays of identically folded domains, referred to as “beads-on-a-string”. It remains a largely unresolved question how these domains have developed a unique molecular profile such that each carries out a distinct function without false-positive readout. This study focuses on the M-band segment of the sarcomeric protein titin, which comprises ten identically folded immunoglobulin domains. Comparative analysis of high-resolution structures of six of these domains ‒ M1, M3, M4, M5, M7, and M10 ‒ reveals considerable structural diversity within three distinct loops and a non-conserved pattern of exposed cysteines. Our data allow to structurally interpreting distinct pathological readouts that result from titinopathy-associated variants. Our findings support general principles that could be used to identify individual structural/functional profiles of hundreds of identically folded protein domains within the sarcomere and other densely crowded cellular environments.

Heterozygous RHO p.R135W missense mutation in a large Han-Chinese family with retinitis pigmentosa and different refractive errors

Retinitis pigmentosa (RP), the most common type of inherited retinal degeneration causing blindness, initially manifests as severely impaired rod function followed by deteriorating cone function. Mutations in the rhodopsin gene (RHO) are the most common cause of autosomal dominant RP (adRP). The present study aims to identify the disease-causing mutation in a numerous, four-generation Han-Chinese family with adRP detected by whole exome sequencing and Sanger sequencing. Afflicted family members present classic adRP along with heterogeneous clinical phenotypes including differing refractive errors, cataracts, astigmatism and epiretinal membranes. A missense mutation, c.403C>T (p.R135W), in the RHO gene was identified in nine subjects and it co-segregated with family members. The mutation is predicted to be disease-causing and results in rhodopsin protein abnormalities. The present study extends the genotype-phenotype relationship between RHO gene mutations and adRP clinical findings. The results have implications for familial genetic counseling, clinical management and developing RP target gene therapy strategies.

A novel mutation in TTN gene in a Saudi patient with bilateral facial weakness and scapular winging

Titin (TTN) is a large gene with 363 exons that encodes a large abundant protein (longest known polypeptide in nature) that is expressed in cardiac and skeletal muscles. TTN has an important role in the sarcomere organization, assembly of muscles, transmission of the force at the Z-line, passive myocyte stiffness, and resting tension maintenance in the I-band region. Mutation in extreme C terminus of TTN, situated at the end of M-band of the TTN in chromosome 2q31, results in tibial muscular dystrophy (TMD), also called Udd Distal Myopathy, which is an autosomal dominant distal myopathy. In this article, we report a novel mutation in TTN gene in a Saudi patient with bilateral facial weakness and scapular winging. This report adds to the literature a heterozygous missense variant c.85652C>G, p.(Pro28551Arg) in TTN gene, which may be related to genes that cause the disease, but more case validation is needed. The novel mutation described in the present study widened the genetic spectrum of TTN-associated diseases, which may benefit studies addressing this disease in the future.

Titin in muscular dystrophy and cardiomyopathy: Urinary titin as a novel marker

Titin, encoded by the gene TTN, is the largest human protein, and plays central roles in sarcomeric structures and functions in skeletal and cardiac muscles. Mutations of TTN are causally related to specific types of muscular dystrophies and cardiomyopathies. A developed methodology of next generation sequencing has recently led to the identification of novel TTN mutations in such diseases. The clinical significance of titin is now emerging as a target for genetic strategies. Titin-related muscular dystrophies include tibial muscular dystrophy, limb-girdle muscular dystrophy, Emery-Dreifuss muscular dystrophy, hereditary myopathy with early respiratory failure, central core myopathy, centronuclear myopathies, and Salih myopathy. Truncation mutations of TTN have been identified as the most frequent genetic cause of dilated cardiomyopathy. In this review article, we highlight the role of titin and impact of TTN mutations in the pathogenesis of muscular dystrophies and cardiomyopathies. Recently, a novel sensitive sandwich enzyme-linked immunosorbent assay (ELISA) for the detection of the urinary titin N-terminal fragments (U-TN) has been established. We discuss the clinical significance of U-TN in the diagnosis of muscular dystrophies and differential diagnosis of cardiomyopathies, as well as risk stratification in dilated cardiomyopathy.

Identification of a Heterozygous Mutation in the TGFBI Gene in a Hui-Chinese Family with Corneal Dystrophy

Background/Aims

Corneal dystrophies (CDs) belong to a group of hereditary heterogeneous corneal diseases which result in visual impairment due to the progressive accumulation of deposits in different corneal layers. So far, mutations in several genes have been responsible for various CDs. The purpose of this study is to identify gene mutations in a three-generation Hui-Chinese family associated with granular corneal dystrophy type I (GCD1).

Methods

A three-generation Hui-Chinese pedigree with GCD1 was recruited for this study. Slit-lamp biomicroscopy, optical coherence tomography, and confocal microscopy were performed to determine the clinical features of available members. Whole exome sequencing was performed on two patients to screen for potential disease-causing variants in the family. Sanger sequencing was used to test the variant in the family members.

Results

Clinical examinations demonstrated bilaterally abundant multiple grayish-white opacities in the basal epithelial and superficial stroma layers of corneas of the two patients. Whole exome sequencing revealed that a heterozygous missense mutation (c.1663C > T, p.Arg555Trp) in the transforming growth factor beta-induced gene (TGFBI) was shared by the two patients, and it cosegregated with this disease in the family confirmed by Sanger sequencing.

Conclusions

The results suggested that the heterozygous TGFBI c.1663C > T (p.Arg555Trp) mutation was responsible for GCD1 in the Hui-Chinese family, which should be of great help in genetic counseling for this family.

Prevalence, pathological mechanisms, and genetic basis of limb-girdle muscular dystrophies: A review

Limb-girdle muscular dystrophies (LGMDs) are a highly heterogeneous group of neuromuscular disorders that are associated with weakness and wasting of muscles in legs and arms. Signs and symptoms may begin at any age and usually worsen by time. LGMDs are autosomal disorders with different types and their prevalence is not the same in different areas. New technologies such as next-generation sequencing can accelerate their diagnosis. Several important pathological mechanisms that are involved in the pathology of the LGMD include abnormalities in dystrophin-glycoprotein complex, the sarcomere, glycosylation of dystroglycan, vesicle and molecular trafficking, signal transduction pathways, and nuclear functions. Here, we provide a comprehensive review that integrates LGMD clinical manifestations, prevalence, and some pathological mechanisms involved in LGMDs.

Increasing Role of Titin Mutations in Neuromuscular Disorders

The TTN gene with 363 coding exons encodes titin, a giant muscle protein spanning from the Z-disk to the M-band within the sarcomere. Mutations in the TTN gene have been associated with different genetic disorders, including hypertrophic and dilated cardiomyopathy and several skeletal muscle diseases.

Before the introduction of next generation sequencing (NGS) methods, the molecular analysis of TTN has been laborious, expensive and not widely used, resulting in a limited number of mutations identified. Recent studies however, based on the use of NGS strategies, give evidence of an increasing number of rare and unique TTN variants. The interpretation of these rare variants of uncertain significance (VOUS) represents a challenge for clinicians and researchers.

The main aim of this review is to describe the wide spectrum of muscle diseases caused by TTN mutations so far determined, summarizing the molecular findings as well as the clinical data, and to highlight the importance of joint efforts to respond to the challenges arising from the use of NGS. An international collaboration through a clinical and research consortium and the development of a single accessible database listing variants in the TTN gene, identified by high throughput approaches, may be the key to a better assessment of titinopathies and to systematic genotype– phenotype correlation studies.

Association of the AADAC gene and Tourette syndrome in a Han Chinese cohort

Tourette syndrome (TS) is a complex neuropsychiatric disorder with chronic motor and vocal tics. Though the etiology is elusive, strong evidence for a genetic contribution to TS has been established. To date, various chromosomal or genetic alterations have been implicated in its pathogenesis. Recently, the deletion in the arylacetamide deacetylase gene (AADAC) was reported to be associated with TS. To investigate the association between the AADAC gene variants and TS, we conducted genetic analysis of the AADAC gene in 200 Han Chinese patients and 300 ethnicity-matched normal controls. Two variants, including a heterozygous splice-site variant, c.361 + 1G > A (rs762169706), and a missense variant, c.744A > T (p.R248S, rs186388618), were identified in two unrelated patients. The c.361 + 1G > A variant, absent in 300 ethnicity-matched controls, led to the deletion of exon 2 in AADAC mRNA, probably associated with development of TS. The c.744A > T variant, predicted to be damaging, was identified in two normal controls. The findings indicate that the AADAC gene c.361 + 1G > A variant may be a potential candidate factor for TS development, though further investigations are warranted.

Compound heterozygous POMT1 mutations in a Chinese family with autosomal recessive muscular dystrophy-dystroglycanopathy C1

Muscular dystrophy-dystroglycanopathy (MDDG) is a genetically and clinically heterogeneous group of muscular disorders, characterized by congenital muscular dystrophy or later-onset limb-girdle muscular dystrophy accompanied by brain and ocular abnormalities, resulting from aberrant alpha-dystroglycan glycosylation. Exome sequencing and Sanger sequencing were performed on a six-generation consanguineous Han Chinese family, members of which had autosomal recessive MDDG. Compound heterozygous mutations, c.1338+1G>A (p.H415Kfs*3) and c.1457G>C (p.W486S, rs746849558), in the protein O-mannosyltransferase 1 gene (POMT1), were identified as the genetic cause. Patients that exhibited milder MDDG manifested as later-onset progressive proximal pelvic, shoulder girdle and limb muscle weakness, joint contractures, mental retardation and elevated creatine kinase, without structural brain or ocular abnormalities, were further genetically diagnosed as MDDGC1. The POMT1 gene splice-site mutation (c.1338+1G>A) which leads to exon 13 skipping and results in a truncated protein may contribute to a severe phenotype, while the allelic missense mutation (p.W486S) may reduce MDDG severity. These findings may expand phenotype and mutation spectrum of the POMT1 gene. Clinical diagnosis supplemented with molecular screening may result in more accurate diagnoses of, prognoses for, and improved genetic counselling for this disease.

A customized high-resolution array-comparative genomic hybridization to explore copy number variations in Parkinson's disease

Parkinson’s disease (PD), the second most common progressive neurodegenerative disorder, was long believed to be a non-genetic sporadic syndrome. Today, only a small percentage of PD cases with genetic inheritance patterns are known, often complicated by reduced penetrance and variable expressivity. The few well-characterized Mendelian genes, together with a number of risk factors, contribute to the major sporadic forms of the disease, thus delineating an intricate genetic profile at the basis of this debilitating and incurable condition. Along with single nucleotide changes, gene-dosage abnormalities and copy number variations (CNVs) have emerged as significant disease-causing mutations in PD. However, due to their size variability and to the quantitative nature of the assay, CNV genotyping is particularly challenging. For this reason, innovative high-throughput platforms and bioinformatics algorithms are increasingly replacing classical CNV detection methods. Here, we report the design strategy, development, validation and implementation of NeuroArray, a customized exon-centric high-resolution array-based comparative genomic hybridization (aCGH) tailored to detect single/multi-exon deletions and duplications in a large panel of PD-related genes. This targeted design allows for a focused evaluation of structural imbalances in clinically relevant PD genes, combining exon-level resolution with genome-wide coverage. The NeuroArray platform may offer new insights in elucidating inherited potential or de novo structural alterations in PD patients and investigating new candidate genes.

A novel heterozygous COL4A4 missense mutation in a Chinese family with focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is the most common glomerular histological lesion associated with high-grade proteinuria and end-stage renal disease. Histologically, FSGS is characterized by focal segmental sclerosis with foot process effacement. The aim of this study was to identify the disease-causing mutation in a four-generation Chinese family with FSGS. A novel missense mutation, c.1856G>A (p.Gly619Asp), in the collagen type IV alpha-4 gene (COL4A4) was identified in six patients and it co-segregated with the disease in this family. The variant is predicted to be disease-causing and results in collagen IV abnormalities. Our finding broadens mutation spectrum of the COL4A4 gene and extends the phenotypic spectrum of collagen IV nephropathies. Our study suggests that exome sequencing is a cost-effective and efficient approach for identification of disease-causing mutations in phenotypically complex or equivocal disorders. Timely screening for COL4A3/COL4A4 mutations in patients with familial FSGS may help both accurately diagnose and treat these patients.