Partial loss of desmin expression due to a leaky splice site variant in the human DES gene is associated with neuromuscular transmission defects.

Recessive desminopathies are rare and often present as severe early-onset myopathy. Here we report a milder phenotype in three unrelated patients from southern India (2 M, 1F) aged 16, 21, and 22 years, who presented with childhood-onset, gradually progressive, fatigable limb-girdle weakness, ptosis, speech and swallowing difficulties, without cardiac involvement. Serum creatine kinase was elevated, and repetitive nerve stimulation showed decrement in all. Clinical improvement was noted with pyridostigmine and salbutamol in two patients. All three patients had a homozygous substitution in intron 5: DES(NM_001927.4):c.1023+5G>A, predicted to cause a donor splice site defect. Muscle biopsy with ultrastructural analysis suggested myopathy with myofibrillar disarray, and immunohistochemistry showed partial loss of desmin with some residual staining, while western blot analysis showed reduced desmin. RT-PCR of patient muscle RNA revealed two transcripts: a reduced normal desmin transcript and a larger abnormal transcript suggesting leaky splicing at the intron 5 donor site. Sequencing of the PCR products confirmed the inclusion of intron 5 in the longer transcript, predicted to cause a premature stop codon. Thus, we provide evidence for a leaky splice site causing partial loss of desmin associated with a unique phenotypic presentation of a milder form of desmin-related recessive myopathy overlapping with congenital myasthenic syndrome.

Investigation of mutation spectrum amongst patients with familial primary cardiomyopathy using targeted NGS in Indian population.

Genetic cardiomyopathies (CM) are disorders that affect morphology and function of cardiac muscle. Significant number of genes have been implicated in causing the phenotype. It is one of the leading genetic causes of death in young. We performed a study to understand the genetic variants in primary cardiomyopathies in an Indian cohort. Study comprised of 22 probands (13 with family history) representing hypertrophic (n = 10), dilated (n = 7), restrictive (n = 2) and arrhythmogenic ventricular(n = 3) cardiomyopathies. Genomic DNA was target captured with a panel of 46 genes and libraries sequenced on Illumina platform. Analysis identified, reported pathogenic as well as novel pathogenic (n = 6) variants in 16 probands. Of the 10 HCM patients, candidate variants were identified in nine of them involving sarcomere genes (62%, MYBPC3, MYH6, MYH7, MYL3, TTN), Z-disc (10%, ACTN2, LDB3, NEXN,), desmosome (10%, DSG2, DSP, PKP2) cytoskeletal (4%, DTNA) and ion channel (10% RYR2). In four DCM patients, variants were identified in genes NEXN, LMNA and TTN. Three arrhythmogenic right ventricular cardiomyopathy (ARVD) patients carried mutations in desmosome genes. Rare TTN variants were identified in multiple patients. Targeted capture and sequencing resulted in identification of candidate variants in about 70% of the samples which will help in management of disease in affected individual as well as in screening and early diagnosis in asymptomatic family members. Amongst the analysed cases, 22% were inconclusive without any significant variant identified. Study illustrates the utility of next-generation multi-gene panel as a cost-effective genetic testing to screen all forms of primary cardiomyopathies.

Myotonic Dystrophy Type 1 (DM1): Clinical Characteristics and Disease Progression in a Large Cohort.

BACKGROUND: DM1 is a multisystem disorder caused by expansion of a CTG triplet repeat in the 3' non-coding region of DMPK. Neuropsychological consequences and sleep abnormalities are important associations in DM1. OBJECTIVE: To describe the clinical phenotype, disease progression and characterize the sleep alterations and cognitive abnormalities in a sub-set of patients. MATERIALS AND METHODS: A retrospective study on 120 genetically confirmed DM1 cases. Findings in neuropsychological assessment and multiple sleep questionnaires were compared with 14 age and sex matched healthy individuals. All 120 patients were contacted through letters/telephonic consultation/hospital visits to record their latest physical and functional disabilities. RESULTS: The mean age at symptom onset was 23.1 ± 11.4 years, M: F = 3.8:1, mean duration of illness = 14.3 ± 9.5 years. Clinically 54.2% had adult onset form, juvenile = 27.5%, infantile = 10.8%, late adult onset = 7.5%. Paternal transmission occurred more frequently. The predominant initial symptoms were myotonia (37.5%), hand weakness (21.7%), lower limb weakness (23.3%) and bulbar (10%). Twenty patients completed sleep questionnaires (SQ). Abnormal scores were noted in Epworth sleepiness scale (55%); Pittsburgh sleep quality index (45%); Berlin SQ (30%); Rapid eye movement sleep Behaviour Disorder SQ (15%); Restless leg syndrome rating scale (10%). Neuropsychological assessment of 20 patients revealed frontal executive dysfunction, attention impairment and visuospatial dysfunction. Frontal lobe was most affected (72%) followed by parietal (16%) and temporal lobe (12%). CONCLUSIONS: The current study provides a comprehensive account of the clinical characteristics in Indian patients with DM1. Hypersomnolence was most commonly seen. Excessive daytime sleepiness and Sleep disordered breathing were the most common sleep related abnormality. Cognitive impairment comprised predominantly of frontal lobe dysfunction.

Generation of induced pluripotent stem cell line, NIMHi009-A, from PBMCs of an adult healthy male.

Human induced pluripotent stem cells provide an exceptional platform for studying pathogenesis in vitro. We, therefore, have generated and characterized human induced pluripotent stem cell (iPSC) line NIMHi009-A derived from peripheral blood mononuclear cells (PBMCs) of healthy adult male control for an epileptic patient carrying voltage gated sodium channel mutation, using Sendai virus-based reprogramming. The generated iPSCs express pluripotency genes and can spontaneously differentiate into three germ layers. These cells display a normal karyotype and are free of mycoplasma. The iPSC line NIMHi009-A can be used as healthy control for modelling various diseases and screening for drugs.

Generation of induced pluripotent stem cell line NIMHi010-A from dermal fibroblast cells of a healthy individual.

In this study, we have established human induced pluripotent stem cell (hiPSC) line, NIMHi010-A of a 42-year-old healthy donor. The iPSC line was generated from human dermal fibroblasts using Sendai viruses carrying reprogramming factors c-MYC, SOX2, KLF4, and OCT4 under a feeder-free culture system. The generated hiPSC line expressed typical pluripotency markers, displayed a normal karyotype, and demonstrated the potential to differentiate into the three germ layers. This hiPSC line will serve as a healthy control model for physiological processes and drug screening of Asian origin from Indian population.

Childhood-Onset Myopathy With Preserved Ambulation Caused by a Recurrent ADSSL1 Missense Variant.

Background and Objectives: Distal myopathies are a heterogeneous group of primary muscle disorders with recessive or dominant inheritance. ADSSL1 is a muscle-specific adenylosuccinate synthase isoform involved in adenine nucleotide synthesis. Recessive pathogenic variants in the ADSSL1 gene located in chromosome 14q32.33 cause a distal myopathy phenotype. In this study, we present the clinical and genetic attributes of 6 Indian patients with this myopathy. Methods: This was a retrospective study describing on Indian patients with genetically confirmed ADSSL1 myopathy. Details were obtained from the medical records. Results: All patients presented in their first or early second decade. All had onset in the first decade with a mean age at presentation being 17.7 ± 8.4 years (range: 3-27 years) and M:F ratio being 1:2. The mean disease duration was 9.3 ± 5.2 years ranging from 2 to 15 years. All patients were ambulant with wheelchair bound state in 1 patient due to respiratory involvement. The median serum creatine kinase (CK) level was 185.5 IU/L (range: 123-1564 IU/L). In addition to salient features of ptosis, cardiac involvement, bulbar weakness, and proximo-distal limb weakness with fatigue, there were significant seasonal fluctuations and decremental response to repetitive nerve stimulation, which have not been previously reported. Muscle histopathology was heterogenous with the presence of rimmed vacuoles, nemaline rods, intracellular lipid droplets along with chronic myopathic changes. Subtle response to pyridostigmine treatment was reported. While 5 of 6 patients had homozygous c.781G>A (p.Asp261Asn) variation, 1 had homozygous c.794G>A (p.Gly265Glu) in ADSSL1 gene. Discussion: This study expands the phenotypic spectrum and variability of ADSSL1 myopathy with unusual manifestations in this rare disorder. Because the variant c.781G>A (p.Asp261Asn) is the most common mutation among Indian patients similar to other Asian cohorts, this finding could be useful for genetic screening of suspected patients.

A novel DHTKD1 gene mutation with ALS like presentation: a case report.

DHTKD1 is a nuclear gene that encodes "dehydrogenase E1 and transketolase domain-containing 1", essential in mitochondrial metabolism. First identified in the patients of 2-amino-apidic and 2 oxoapidic aciduria, mutation in this gene has recently been implicated in CMT2Q and ALS. Here we report the case of a septuagenarian who presented with a 2 years progressive history of respiratory and neck muscle weakness without significant bulbar and limb involvement. Clinical and electrophysiological examination revealed lower motor neuron involvement with widespread chronic denervation and reinnervation. Clinical exome sequencing revealed a heterozygous nonsense variant in exon 8 of the DHTKD1 gene, which was previously described in CMT2Q. This report highlights the pleotropic phenotypic presentation of DHTKD1 mutation and the need for genetic testing even in sporadic cases of ALS presenting at a later age.

Clinical and genetic characterisation of a large Indian congenital myasthenic syndrome cohort.

Congenital myasthenic syndromes (CMS) are a rare group of inherited disorders caused by gene defects associated with the neuromuscular junction and potentially treatable with commonly available medications such as acetylcholinesterase inhibitors and ß2 adrenergic receptor agonists. In this study, we identified and genetically characterized the largest cohort of CMS patients from India to date. Genetic testing of clinically suspected patients evaluated in a South Indian hospital during the period 2014-19 was carried out by standard diagnostic gene panel testing or using a two-step method that included hotspot screening followed by whole-exome sequencing. In total, 156 genetically diagnosed patients (141 families) were characterized and the mutational spectrum and genotype-phenotype correlation described. Overall, 87 males and 69 females were evaluated, with the age of onset ranging from congenital to fourth decade (mean 6.6 ± 9.8 years). The mean age at diagnosis was 19 ± 12.8 (1-56 years), with a mean diagnostic delay of 12.5 ± 9.9 (0-49 years). Disease-causing variants in 17 CMS-associated genes were identified in 132 families (93.6%), while in nine families (6.4%), variants in genes not associated with CMS were found. Overall, postsynaptic defects were most common (62.4%), followed by glycosylation defects (21.3%), synaptic basal lamina genes (4.3%) and presynaptic defects (2.8%). Other genes found to cause neuromuscular junction defects (DES, TEFM) in our cohort accounted for 2.8%. Among the individual CMS genes, the most commonly affected gene was CHRNE (39.4%), followed by DOK7 (14.4%), DPAGT1 (9.8%), GFPT1 (7.6%), MUSK (6.1%), GMPPB (5.3%) and COLQ (4.5%). We identified 22 recurrent variants in this study, out of which eight were found to be geographically specific to the Indian subcontinent. Apart from the known common CHRNE variants p.E443Kfs*64 (11.4%) and DOK7 p.A378Sfs*30 (9.3%), we identified seven novel recurrent variants specific to this cohort, including DPAGT1 p.T380I and DES c.1023+5G>A, for which founder haplotypes are suspected. This study highlights the geographic differences in the frequencies of various causative CMS genes and underlines the increasing significance of glycosylation genes (DPAGT1, GFPT1 and GMPPB) as a cause of neuromuscular junction defects. Myopathy and muscular dystrophy genes such as GMPPB and DES, presenting as gradually progressive limb girdle CMS, expand the phenotypic spectrum. The novel genes MACF1 and TEFM identified in this cohort add to the expanding list of genes with new mechanisms causing neuromuscular junction defects.

Adult Onset Episodic Encephalopathy Due to Citrin Deficiency-A Case Report.

Hyperammonemia is a rare cause of adult episodic encephalopathy. Citrin deficiency resulting in citrullinemia type 2 (CTLN2) can lead to recurrent delirium in adults. Here we report a case of adult onset episodic encephalopathy due to citrin deficiency. A 40 years old male presented with one-year history of episodic encephalopathy triggered by high protein and fat diet. He also had chronic pancreatitis and subacute intestinal obstruction which is a novel manifestation of CTLN2. Evaluation showed elevated blood liver enzymes, ammonia, and citrulline. MRI brain showed frontal hyperintensities and bulky basal ganglia which have not been reported. Diagnosis was confirmed by next-generation sequencing which showed a novel variant c. 1591G > A in exon15 of SLC25A13. Hyperammonemic syndromes should be considered in differential diagnosis of episodic encephalopathy in adults. This report shows novel features of subacute intestinal obstruction and MRI findings in CTLN2 expanding spectrum of manifestation.

Childhood Neurological Disorders With Hyperhomocystinemia: A Case-Based Review.

Hyperhomocysteinemia is a rare neurometabolic syndrome with diverse manifestations in the pediatric age group, thereby posing a diagnostic challenge. Biochemical testing is imperative to guide plan of evaluation, which may include appropriate genetic testing, in inherited disorders. Through this case-based approach, we demonstrate the heterogeneity of clinical presentation, biochemical and genetic evaluation, and treatment strategies that may reverse this condition among children.

Generation and characterisation of a human induced pluripotent stem cell line, NIMHi007-A, from peripheral blood mononuclear cells derived from an adult healthy female.

We report the generation and characterisation of a human induced pluripotent stem cell (iPSC) line, NIMHi007-A, derived from peripheral blood mononuclear cells (PBMCs) of a healthy female adult individual. PBMCs were reprogrammed using the non-integrating Sendai virus consisting of Yamanaka reprogramming factors- SOX2, cMYC, KLF4, and OCT4. The iPSCs displayed a normal karyotype, express pluripotency markers, and could generate into three germ layers, endoderm, mesoderm, and ectoderm, in-vitro. This iPSC line, NIMHi007-A, can be used as a healthy control for various in-vitro disease models and study their underlying pathophysiological mechanisms.

MYH2-related Myopathy: Expanding the Clinical Spectrum of Chronic Progressive External Ophthalmoplegia (CPEO).

Chronic progressive external ophthalmoplegia (CPEO) is symptom complex with progressive ptosis and restricted ocular motility without diplopia. MYH2 myopathy is rare disorder presenting with CPEO and muscle weakness. We report two Indian patients of MYH2 myopathy with unique features. Patient-1 presented with early adult-onset esophageal reflux followed by, proximal lower limb weakness, proptosis, CPEO without ptosis. He had elevated creatine kinase along with characteristic muscle MRI findings of prominent semitendinosus and medial gastrocnemius involvement. Patient -2 presented with early adult onset CPEO without limb weakness. His creatine kinase was normal. Both the patients had novel MYH2 mutations: a homozygous 5'splice variation in intron 4 (c.348 + 2dup) in patient 1 and homozygous single base pair deletion in exon 32 (p. Ala1480ProfsTer11) in patient 2. Unique features noted include adult onset, isolated CPEO, proptosis, esophageal reflux disease and absence of skeletal abnormalities. MYH2 myopathy has to be considered in adult patients with CPEO.

TEFM variants impair mitochondrial transcription causing childhood-onset neurological disease.

Mutations in the mitochondrial or nuclear genomes are associated with a diverse group of human disorders characterized by impaired mitochondrial respiration. Within this group, an increasing number of mutations have been identified in nuclear genes involved in mitochondrial RNA biology. The TEFM gene encodes the mitochondrial transcription elongation factor responsible for enhancing the processivity of mitochondrial RNA polymerase, POLRMT. We report for the first time that TEFM variants are associated with mitochondrial respiratory chain deficiency and a wide range of clinical presentations including mitochondrial myopathy with a treatable neuromuscular transmission defect. Mechanistically, we show muscle and primary fibroblasts from the affected individuals have reduced levels of promoter distal mitochondrial RNA transcripts. Finally, tefm knockdown in zebrafish embryos resulted in neuromuscular junction abnormalities and abnormal mitochondrial function, strengthening the genotype-phenotype correlation. Our study highlights that TEFM regulates mitochondrial transcription elongation and its defect results in variable, tissue-specific neurological and neuromuscular symptoms.