Distal Myopathy Research Articles

Clinical, Histopathologic, and Genetic Features of Patients With Myofibrillar and Distal Myopathies: Experience From the Italian Network.

Clinical, Histopathologic, and Genetic Features of Patients With Myofibrillar and Distal Myopathies: Experience From the Italian Network.

MYH7-related myopathies: clinical, myopathological and genotypic spectrum in a multicentre French cohort

BackgroundMyosin heavy chain 7 (MYH7)-related myopathies (MYH7-RMs) are a group of muscle disorders linked to pathogenic variants in the MYH7 gene, encoding the slow/beta-cardiac myosin heavy chain, which is highly...

Late-onset primary muscle diseases mimicking sarcopenia.

Sarcopenia is an age-related loss of skeletal muscle mass, strength, and function that causes various health problems. In contrast, late-onset primary myopathies, which occur in the older population, are caused by a variety of factors, including genetic mutations, autoimmune processes, and metabolic abnormalities. Although sarcopenia and primary myopathy are two distinct disease processes, their symptoms can overlap, making differentiation challenging. The diagnostic criteria for sarcopenia have evolved over time, and various criteria have been proposed by expert groups. Late-onset primary muscle diseases such as inclusion body myositis, sporadic late-onset nemaline myopathy, muscular dystrophies, distal myopathies, myofibrillar myopathies, metabolic myopathies, and mitochondrial myopathies share common pathogenic mechanisms with sarcopenia, further complicating the diagnostic process. Appropriate clinical evaluation, including detailed history-taking, physical examination, and diagnostic testing, is essential for accurate diagnosis and management. Treatment approaches, including exercise, nutritional support, and disease-specific therapies, must be tailored to the characteristics of each disease. Despite these differences, sarcopenia and primary myopathies require careful consideration in the clinical setting for proper diagnosis and management. This review outlines the evolution of diagnostic criteria and diagnostic items for sarcopenia, late-onset primary myopathies that should be differentiated from sarcopenia, common pathomechanisms, and diagnostic algorithms to properly differentiate primary myopathies. Geriatr Gerontol Int 2024; ••: ••-••.

56P Mutational screening of distal myopathy gene ACTN2 reveals an aggregation hot-spot in the actin-binding domain

56P Mutational screening of distal myopathy gene ACTN2 reveals an aggregation hot-spot in the actin-binding domain

63P Identifying the disease-causing variant in a large family, with a late-onset dominant distal myopathy

63P Identifying the disease-causing variant in a large family, with a late-onset dominant distal myopathy

62P Axial involvement as a prominent feature in SMPX-related distal myopathy

62P Axial involvement as a prominent feature in SMPX-related distal myopathy

Role of biomarkers of inflammation and MRI technique for the early detection of cystinosis-associated myopathy

BackgroundCystinosis is an autosomal recessive lysosomal storage disorder caused by cystine crystals accumulation within lysosomes resulting in multi-organ dysfunction. Infantile nephropathic cystinosis is the most common phenotype of the disease. Cystinosis distal myopathy was first described in 1994 with a 24% prevalence in cystinosis adult patients.MethodsWe prospectively evaluated the clinical, biochemical, and radiological data of 22 nephropathic cystinosis pediatric patients from 19 unrelated families (17 males and 5 females, their ages 105.7 ± 41.5 months) recruited at the cystinosis clinic at Cairo University Children’s Hospital. Biochemical assessment included several inflammatory biomarkers, such as CRP, ESR, chitotriosidase, and galectin-3. We further performed conventional MRI for the muscles of both upper and lower limbs for potential detection of early myopathic involvement. We compared these findings with 44 CKD children as pathological controls and 22 healthy pediatric controls.ResultsClinically, no evidence of neuromuscular involvement was detected in our cystinosis pediatric cohort. Chitotriosidase was elevated significantly in cystinosis patients compared to CKD controls. Regarding MRI, morphologically, there were no significant differences between the muscles of cystinosis patients and healthy controls.ConclusionA significantly higher chitotriosidase activity in cystinosis patients seems to better represent the overall disease burden and cannot be linked to neuromuscular involvement. MRI findings in muscles of the cystinosis cohort are not striking and indicate no early changes at a younger age. Follow-up and further studies for higher age groups are required to accurately elucidate the MRI’s role in assessing cystinosis myopathy.

Heterozygous loss-of-function variants in SPTAN1 cause a novel early childhood onset distal myopathy with chronic neurogenic features.

Neurogenetic disorders caused by pathogenic variants in four genes encoding non-erythrocytic spectrins ( SPTAN1, SPTBN1, SPTBN2, SPTBN4) range from peripheral and central nervous system involvement to complex syndromic presentations. Heterozygous pathogenic variants in SPTAN1 are exemplary for this diversity with phenotypes spanning almost the entire spectrum. Through international collaboration we identified 14 families with genetically unsolved distal weakness and unreported heterozygous SPTAN1 loss-of-function variants including frameshift, nonsense and splice-acceptor variants. Clinical data, electrophysiology, muscle CT or MRI and muscle biopsy findings were collected and standardized. SPTAN1 protein, mRNA expression analysis and cDNA sequencing was performed on muscle tissue from two patients. All 20 patients presented with early childhood onset distal weakness. The severity varied both within families and between different families. Foot abnormalities ranged from hammer toes and pes cavus to distal arthrogryposis. Electrophysiology showed mixed myogenic and neurogenic features. Muscle MRI or CT in 10 patients showed fatty infiltration of the distal lower limb anterior compartment and/or selective involvement of the extensor hallucis longus muscle. Muscle biopsy revealed myopathic changes with mild dystrophic and chronic neurogenic changes in 7 patients. Finally, we provide proof for nonsense mediated decay in tissues derived from two patients. We provide evidence for the association of SPTAN1 loss-of-function variants with childhood onset distal myopathy in 14 families. This finding extends the phenotypic spectrum of SPTAN1 loss-of-function variants ranging from intellectual disability to distal weakness with a predominant myogenic cause. SPTAN1 loss-of-function variants, including frameshift, nonsense and splice site variants cause a novel childhood onset distal weakness syndrome with primarily skeletal muscle involvement. Hereditary motor neuropathies and distal myopathic disorders present a well-known diagnostic challenge as they demonstrate substantial clinical and genetic overlap. The emergence of SPTAN1 loss-of-function variants serves as a noteworthy example, highlighting a growing convergence in the spectrum of genotypes linked to both hereditary motor neuropathies and distal myopathies.

Genomic and phenotypic landscapes of X-linked hereditary hearing loss in the Chinese population

BackgroundHearing loss (HL) is the most common sensory birth deficit worldwide, with causative variants in more than 150 genes. However, the etiological contribution and clinical manifestations of X-linked inheritance in HL remain unclear within the Chinese HL population. In this study, we focused on X-linked hereditary HL and aimed to assess its contribution to hereditary HL and identify the genotype–phenotype relationship.MethodsWe performed a molecular epidemiological investigation of X-linked hereditary HL based on next-generation sequencing and third-generation sequencing in 3646 unrelated patients with HL. We also discussed the clinical features associated with X-linked non-syndromic HL-related genes based on a review of the literature.ResultsWe obtained a diagnostic rate of 52.72% (1922/3646) among our patients; the aggregate contribution of HL caused by genes on the X chromosome in this cohort was ~ 1.14% (22/1922), and POU3F4 variants caused ~ 59% (13/22) of these cases. We found that X-linked HL was congenital or began during childhood in all cases, with representative audiological profiles or typical cochlear malformations in certain genes. Genotypic and phenotypic analyses showed that causative variants in PRPS1 and AIFM1 were mainly of the missense type, suggesting that phenotypic variability was correlated with the different effects that the replaced residues exert on structure and function. Variations in SMPX causing truncation of the protein product were associated with DFNX4, which resulted in typical audiological profiles before and after the age of 10 years, whereas nontruncated proteins typically led to distal myopathy. No phenotypic differences were identified in patients carrying POU3F4 or COL4A6 variants.ConclusionsOur work constitutes a preliminary evaluation of the molecular contribution of X-linked genes in heritable HL (~ 1.14%). The 15 novel variants reported here expand the mutational spectrum of these genes. Analysis of the genotype–phenotype relationship is valuable for X-linked HL precise diagnostics and genetic counseling. Elucidation of the pathogenic mechanisms and audiological profiles of HL can also guide choices regarding treatment modalities.

GNE Myopathy: Genotype - Phenotype Correlation and Disease Progression in an Indian Cohort.

GNE myopathy is a rare slowly progressive adult-onset distal myopathy with autosomal recessive inheritance. It has distinctive features of quadriceps sparing with preferential anterior tibial involvement. Most patients eventually become wheelchair bound by 10-20 years after onset. This study analyzes the phenotype-genotype characteristics and disease progression in a large cohort of GNEM patients from India. Retrospective observational study on GNEM from a quaternary neurology referral hospital in southern India. Data was collected from clinical phenotyping, serum creatine kinase levels, muscle biopsy histopathology, genetic analysis and functional assessment scales - IBMFRS and MDFRS. 157 patients were included with mean age at onset and diagnosis: 26.5±6.2 years and 32.8±7.8 years, respectively. M:F ratio was 25 : 13. Most common presenting symptom: foot drop (46.5%) and limb girdle weakness (19.1%). Wasting and weakness of small muscles of hand and finger flexors seen in 66.2% and as an initial symptoms in 5.2%. Though tibialis anterior involvement was most common (89.2%), early quadriceps weakness was noted in 3.2% and Beevor's sign in 59.2%. Rimmed vacuoles were present in 75% of patients with muscle biopsy. Most common variant was the Indian Founder variant identified in 129 patients (c.2179 G>A, p.Val727Met - 82.2%) and most common zygosity being compound heterozygous state (n = 115, 87.5%). Biallelic kinase domain variations predisposed to a more severe phenotype. Wheelchair bound state noted in 8.9% with a mean age and duration of 32.0±7.1 and 6.3±4.9 years respectively, earlier than previous studies on other ethnic groups. This is the largest GNEM cohort reported from South Asia. The p.Val727Met variant in compound heterozygous state is noted in majority (82.2%) of the cases. Observed relationships between genotype and clinical parameters shows that severity of the disease might be attributable to specific GNE genotype and thus could aid in predicting the disease progression.

Diverse Phenotypic Presentation of the Welander Distal Myopathy Founder Mutation, With Myopathy and Amyotrophic Lateral Sclerosis in the Same Family.

Welander distal myopathy is a rare myopathy with prominent and early involvement of distal upper extremity muscles, prevalent in individuals of Scandinavian origin, and caused by a founder mutation in the cytotoxic granule-associated RNA-binding protein (T-cell intracellular antigen-1; TIA1), E384K. Different pathogenic variants in the TIA1 gene, distinct from the founder 1, have recently been associated with frontotemporal dementia and amyotrophic lateral sclerosis (ALS), suggesting that TIA1-related disorders belong to the group of multisystem proteinopathies. We describe the first case of a two-generation family with the founder E384K TIA1 mutation demonstrating phenotypic variability; the mother manifested as Welander myopathy, whereas 2 daughters manifested as ALS. No other genetic cause of ALS was found in 1 of the affected daughters. We also discuss the possible mechanisms explaining this pleotropic presentation of the founder mutation.

Clinical, Histopathologic, and Genetic Features of Patients With Myofibrillary and Distal Myopathies: Experience From the Italian Network.

The diagnostic process for myofibrillar myopathies (MFM) and distal myopathies (DM) is particularly complex because of the large number of causative genes, the existence of still molecularly undefined disease entities, and the overlapping features between the 2 categories. This study aimed to characterize a large cohort of patients affected by MFM and DM and identify the most important diagnostic and prognostic aspects of these diseases. Patients with either a myopathological diagnosis of MFM or a clinical diagnosis of DM were included in this retrospective multicentric national study. Demographic, genetic, clinical, and histopathologic data of anonymized patients were collected from the neuromuscular centers of the Italian Association of Myology network. Data regarding 132 patients with MFM (mean age 57.0 ± 15.8 years, 49% female) and 298 patients with DM (mean age 50.7 ± 15.9 years, 40% female) were gathered from 20 neuromuscular centers. 69 patients fulfilled the criteria for both groups (distal myopathies with myofibrillar pathology, DM-MP). Molecular confirmation was achieved in 63% of the patients. Fifty-two percent of the patients with MFM carried pathogenic variants in either DES (n = 30), MYOT (n = 20), or DNAJB6 (n = 18), which were also the most frequent disease-causing genes in DM-MP, while GNE (n = 44) and MYH7 (n = 23) were the genes most commonly carrying pathogenic variants in DM. The mean age at onset varied from <25 years in patients with causative variants in MYH7 and DYSF to 59 years in patients with myotilinopathies. Cardiac involvement was reported in 29% of patients with MFM and 16% of patients with DM, with DES and MYH7 variants significantly associated with the development of cardiomyopathy. Respiratory impairment was more prevalent in patients with TTN and DES variants and rare in other disorders such as GNE myopathy and dysferlinopathies, which were instead associated, together with DNAJB6-related and PLIN4-related myopathies, with the risk of losing ambulation during the disease course. The Italian cohort of patients with MFM and DM recapitulates the phenotypic heterogeneity and the partial overlap between the 2 groups. However, in relative contrast to the encountered phenotypic variability, only 5 genes accounted for most of the molecular diagnoses. Specific genetic entities are associated with significantly increased risk of developing cardiorespiratory complications or loss of ambulation, which has relevant prognostic implications.

Protein-extending ACTN2 frameshift variants cause variable myopathy phenotypes by protein aggregation.

The objective of the study is to characterize the pathomechanisms underlying actininopathies. Distal myopathies are a group of rare, inherited muscular disorders characterized by progressive loss of muscle fibers that begin in the distal parts of arms and legs. Recently, variants in a new disease gene, ACTN2, have been shown to cause distal myopathy. ACTN2, a gene previously only associated with cardiomyopathies, encodes alpha-actinin-2, a protein expressed in both cardiac and skeletal sarcomeres. The primary function of alpha-actinin-2 is to link actin and titin to the sarcomere Z-disk. New ACTN2 variants are continuously discovered; however, the clinical significance of many variants remains unknown. Thus, lack of clear genotype-phenotype correlations in ACTN2-related diseases, actininopathies, persists. Functional characterization in C2C12 cell model of several ACTN2 variants is conducted, including frameshift and missense variants associated with dominant and recessive actininopathies. We assess the genotype-phenotype correlations of actininopathies using clinical data from several patients carrying these variants. The results show that the missense variants associated with a recessive form of actininopathy do not cause detectable alpha-actinin-2 aggregates in the cell model. Conversely, dominant frameshift variants causing a protein extension do form alpha-actinin-2 aggregates. The results suggest that alpha-actinin-2 aggregation is the disease mechanism underlying some dominant actininopathies, and thus, we recommend that protein-extending frameshift variants in ACTN2 should be classified as pathogenic. However, this mechanism is likely elicited by only a limited number of variants. Alternative functional characterization methods should be explored to further investigate other molecular mechanisms underlying actininopathies.

A novel variant in the GNE gene in a Malian patient presenting with distal myopathy.

GNE-myopathy (GNE-M) is a rare autosomal recessive disorder caused by variants in the GNE gene. We report a novel variant in GNE causing GNE-M in a Malian family. A 19-year-old male patient from consanguineous marriage was seen for progressive walking difficulty. Neurological examination found predominant distal muscle weakness and atrophy, decreased tendon reflexes, predominating in lower limbs. Electroneuromyography showed an axonal neuropathy pattern. However, whole exome sequencing (WES) revealed a novel biallelic variant in GNE c.1838G > A:p.Gly613Glu, segregating with the phenotype within the family. This study highlights its diagnosis challenges in sub-Saharan Africa and broadens the genetic spectrum of this rare disease.

CGG/CCG Repeat Expansions in LOC642361/NUTM2B-AS1 in Thai Patients With Oculopharyngodistal Myopathy.

This study characterizes oculopharyngodistal myopathy in 4 Thai patients from 3 families with CGG/CCG repeat expansion in LOC642361/NUTM2B-AS1. Repeat-primed PCR analyzed CGG/CCG repeat size in LOC642361/NUTM2B-AS1 in 4 Thai patients suspected of oculopharyngodistal myopathy (OPDM). Clinical records were reviewed for clinicopathologic features. All patients exhibited strong somatic instabilities of the expanded CGG/CCG repeats, primarily manifesting as oculopharyngeal weakness. Patient 1 had mild finger extensor and intrinsic hand muscle weakness, and although patient 2 lacked limb weakness, both siblings showed electrophysiologic evidence of distal myopathy, indicative of OPDM. Patient 3, the daughter of a sibling with OPDM reported in 2004, lacked limb weakness or leukoencephalopathy on brain MRI. Patient 4, initially misdiagnosed with refractory myasthenia gravis, had generalized muscle weakness. While initially characterized as oculopharyngeal myopathy with leukoencephalopathy (OPML) in a Japanese family, our study suggests a stronger association between CGG/CCG expansion in LOC642361/NUTM2B-AS1 and oculopharyngodistal myopathy (OPDM) rather than OPML. The variable presence or absence of leukoencephalopathy further supports OPDM as the predominant clinical manifestation linked to CGG/CCG expansion in LOC642361/NUTM2B-AS1.

Current advance on distal myopathy genetics.

Distal myopathies are a clinically heterogenous group of rare, genetic muscle diseases, that present with weakness in hands and/or feet at onset. Some of these diseases remain accentuated in the distal muscles whereas others may later progress to the proximal muscles. In this review, the latest findings related to genetic and clinical features of distal myopathies are summarized. Variants in SMPX , DNAJB2, and HSPB6 have been identified as a novel cause of late-onset distal myopathy and neuromyopathy. In oculopharyngodistal myopathies, repeat expansions were identified in two novel disease-causing genes, RILPL1 and ABCD3. In multisystem proteinopathies, variants in HNRNPA1 and TARDBP , genes previously associated with amyotrophic lateral sclerosis, have been shown to cause late-onset distal myopathy without ALS. In ACTN2 -related distal myopathy, the first recessive forms of the disease have been described, adding it to the growing list of genes were both dominant and recessive forms of myopathy are present. The identification of novel distal myopathy genes and pathogenic variants contribute to our ability to provide a final molecular diagnosis to a larger number of patients and increase our overall understanding of distal myopathy genetics and pathology.

Muscular Dystrophies: An Update Review

A broad group of illnesses known as muscular dystrophies are defined by pathologic alterations found in muscle tissue following biopsy. A progressive weakening of the skeletal muscles characterises the clinical appearance of these disorders. The most common type of muscular dystrophy is Duchenne Muscular Dystrophy, an X-linked recessive disease. Distal muscular dystrophy is most common in people between the ages of 40 and 60 and primarily affects the lower limbs, such as the hands, feet, arms, and legs. The development of muscle weakness during infancy or early childhood, usually before the age of two, is a common symptom of congenital muscular dystrophy. The majority of MD types frequently result in respiratory issues that affect the diaphragm and other breathing muscles. Several MD subtypes are linked to cardiac arrhythmias or cardiomyopathy. This class of disorders is the main target of gene transfer and gene repair therapies.

Generation of iPSC lines from three Laing distal myopathy patients with a recurrent MYH7 p.Lys1617del variant

Variants in MYH7 cause cardiomyopathies as well as myosin storage myopathy and Laing early-onset distal myopathy (MPD1). MPD1 is characterized by muscle weakness and atrophy usually beginning in the lower legs. Here, we generated iPSC lines from lymphoblastoid cells of three unrelated individuals heterozygous for the most common MPD1-causing variant; p.Lys1617del. iPSC lines showed typical morphology, expressed pluripotency markers, demonstrated trilineage differentiation potential, and had a normal karyotype. These lines represent the first iPSCs derived from MPD1 patients and complement existing MPD1 animal models. They can provide in vitro platforms to better understand and model MPD1 pathomechanisms and test therapies.

A novel mutation alters GNE bifunctional enzyme activity and leads to familial inherited GNE diseases

Distal myopathies are a group of rare heterogeneous diseases that are mostly caused by genetic factors. At least 20 genes have been associated with distal myopathies. We performed whole-exome sequencing to identify the genetic cause of disease in a family with distal myopathy. Following the American College of Medical Genetics and Genomics (ACMG) guidelines, we analyzed the sequencing results and screened suspicious mutations based on mutation frequency, functional impact, and disease inheritance pattern. The harmfulness of the mutations was predicted using bioinformatics methods, and the pathogenic mutations were determined. We identified a novel amino acid mutation (NP_005467.1:p.S663L) on the GNE gene that may cause familial distal myopathy. This mutation is the result of the simultaneous mutation of two adjacent nucleotides (c.1988C > T, c.1989C > A) in the codon. First, we measured the mRNA and protein expression of the GNE gene in the lymphoblastoid cell lines (LCLs) of the probands and their family members. Second, GNE vectors carrying the novel mutation, two other known pathogenic mutations, and the wild-type gene were constructed and transfected into HEK293T cells. The enzymatic activity of these GNE variants was investigated and showed that the p.S663L mutation significantly reduced the activity of the bifunctional GNE enzyme without altering the expression level of the GNE protein. Furthermore, the mutation may also alter the immunogenicity of the 3′ end of the GNE protein, potentially affecting its oligomer formation. In this study, a novel GNE gene mutation that may cause distal myopathy was identified, expanding the spectrum of genetic mutations associated with this disease.

Defining the landscape of TIA1 and SQSTM1 digenic myopathy

TIA1/SQSTM1 myopathy is one of the few digenic myopathies. We describe four new French adult male patients carrying the TIA1 p.Asn357Ser and SQSTM1 p.Pro392Leu variant and review the literature to include 20 additional cases to define the spectrum of the disease. These twenty-four patients (75% males) had late-onset (52,6 ± 10,1 years), mainly asymmetric, distal ankle and hand finger extension weakness (75%), mild CK elevation (82.4%) and myopathic EMG. Two of the four French patients had sensorimotor axonal polyneuropathy and an additional one had neurogenic changes in muscle biopsy. Muscle biopsy showed rimmed vacuoles (44.4%), myofibrillar disorganization (16.7%) or both (38.9%), with P62/TDP43 aggregates. The TIA1 p.Asn357Ser variant was present in all patients and the SQSTM1 p.Pro392Leu was the most frequent (71%) of the four reported SQSTM1 variants. We reviewed the distal myopathy gene panels of Pitié-Salpêtrière's hospital cohort finding a prevalence of 11/414=2.7% of the TIA1 p.Asn357Ser variant, with two patients having an alternative diagnosis (TTN and MYH7) with atypical phenotypes, resembling some of the features seen in TIA1/SQSTM1 myopathy. Overall, TIA1/SQSTM1 myopathy has a homogenous phenotype reinforcing the pathogenicity of its digenic variants. We confirm an increased burden of the TIA1 p.Asn357Ser variant in distal myopathy patients which could act as a genetic modifier.