BET1 is required, together with its SNARE complex partners GOSR2, SEC22b, and Syntaxin‐5 for fusion of endoplasmic reticulum‐derived vesicles with the ER‐Golgi intermediate compartment (ERGIC) and ...the cis‐Golgi. Here, we report three individuals, from two families, with severe congenital muscular dystrophy (CMD) and biallelic variants in BET1 (P1 p.(Asp68His)/p.(Ala45Valfs*2); P2 and P3 homozygous p.(Ile51Ser)). Due to aberrant splicing and frameshifting, the variants in P1 result in low BET1 protein levels and impaired ER‐to‐Golgi transport. Since in silico modeling suggested that p.(Ile51Ser) interferes with binding to interaction partners other than SNARE complex subunits, we set off and identified novel BET1 interaction partners with low affinity for p.(Ile51Ser) BET1 protein compared to wild‐type, among them ERGIC‐53. The BET1/ERGIC‐53 interaction was validated by endogenous co‐immunoprecipitation with both proteins colocalizing to the ERGIC compartment. Mislocalization of ERGIC‐53 was observed in P1 and P2’s derived fibroblasts; while in the p.(Ile51Ser) P2 fibroblasts specifically, mutant BET1 was also mislocalized along with ERGIC‐53. Thus, we establish BET1 as a novel CMD/epilepsy gene and confirm the emerging role of ER/Golgi SNAREs in CMD.
SYNOPSIS
This study describes three individuals with a progressive early‐onset congenital muscular dystrophy, and additional epilepsy in one, caused by biallelic variants in the BET1 gene. BET1, along with its SNARE complex partners, is essential for ER‐to‐Golgi trafficking.
In Family 1, compound heterozygous variants p.(Asp68His)/p.(Ala45Valfs*2) cause aberrant splicing and frameshifting, resulting in very low BET1 protein levels.
Variants in Family 2 (homozygous p.(Ile51Ser)) do not impact BET1 protein levels, interactions with ER‐to‐Golgi SNARE complex members, or SNARE function in yeast.
Mutant Ile51Ser BET1 shows massively reduced binding of the novel Bet1 interaction partner ERGIC‐53, which is also mislocalized in patient fibroblasts.
There is a significant slowing of Golgi‐reconstitution in patient fibroblasts and impaired ER‐to‐Golgi trafficking in HeLa cells.
This study adds to the emerging role of ER/Golgi SNARE dysfunction in the causation of muscular dystrophy.
This study describes three individuals with a progressive early‐onset congenital muscular dystrophy, and additional epilepsy in one, caused by biallelic variants in the BET1 gene. BET1, along with its SNARE complex partners, is essential for ER‐to‐Golgi trafficking.
Only a few small studies have previously reported episodes of hypoglycemia in children with neuromuscular diseases; however, there has been no broader investigation into the occurrence of ...hypoglycemia in children with congenital muscle disease (CMD).
Pediatric patients enrolled in the CMD International Registry (CMDIR) with a history of hypoglycemia were included in this retrospective review. Hypoglycemic episodes and associated clinical and biochemical characteristics were characterized.
Ten patients with CMD (5 with LAMA2-related muscular dystrophy) reported at least one episode of hypoglycemia beginning at an average age of 3.5 years. Predominant symptoms included altered mental status and nausea/vomiting, and laboratory studies demonstrated metabolic acidosis and ketonuria, consistent with ketotic hypoglycemia.
Patients with CMD may have an increased risk of hypoglycemia during fasting, illness, or stress due to their relatively low muscle mass and hence, paucity of gluconeogenic substrate. Clinicians should therefore maintain a high index of suspicion for hypoglycemia in this high-risk patient population and caregivers should routinely be trained to recognize and treat hypoglycemia.
Objective
FHL1‐related reducing body myopathy is an ultra‐rare, X‐linked dominant myopathy. In this cross‐sectional study, we characterize skeletal muscle ultrasound, muscle MRI, and cardiac MRI ...findings in FHL1‐related reducing body myopathy patients.
Methods
Seventeen patients (11 male, mean age 35.4, range 12–76 years) from nine independent families with FHL1‐related reducing body myopathy underwent clinical evaluation, muscle ultrasound (n = 11/17), and lower extremity muscle MRI (n = 14/17), including Dixon MRI (n = 6/17). Muscle ultrasound echogenicity was graded using a modified Heckmatt scale. T1 and STIR axial images of the lower extremity muscles were evaluated for pattern and distribution of abnormalities. Quantitative analysis of intramuscular fat fraction was performed using the Dixon MRI images. Cardiac studies included electrocardiogram (n = 15/17), echocardiogram (n = 17/17), and cardiac MRI (n = 6/17). Cardiac muscle function, T1 maps, T2‐weighted black blood images, and late gadolinium enhancement patterns were analyzed.
Results
Muscle ultrasound showed a distinct pattern of increased echointensity in skeletal muscles with a nonuniform, multifocal, and “geographical” distribution, selectively involving the deeper fascicles of muscles such as biceps and tibialis anterior. Lower extremity muscle MRI showed relative sparing of gluteus maximus, rectus femoris, gracilis, and lateral gastrocnemius muscles and an asymmetric and multifocal, “geographical” pattern of T1 hyperintensity within affected muscles. Cardiac studies revealed mild and nonspecific abnormalities on electrocardiogram and echocardiogram with unremarkable cardiac MRI studies.
Interpretation
Skeletal muscle ultrasound and muscle MRI reflect the multifocal aggregate formation in muscle in FHL1‐related reducing body myopathy and are practical and informative tools that can aid in diagnosis and monitoring of disease progression.
Muscle strength testing is routine in clinical practice. Here we provide an aid to the documentation and visual conceptualization of those results - MuscleViz: a free, open-source application for ...visualizing the results of muscle strength testing. Its use in clinical settings streamlines the communication of physical examination findings. The tool is also useful for presenting patient data in case reports or case series. A push towards free, open-source software has benefitted other areas of science; we believe a similar effort dedicated to the development of clinical tools is worth pursuing.
Calpainopathy, also known as limb girdle muscular dystrophy (LGMD) type 2A (LGMD2A) or LGMD R1 Calpain3-related, is one of the most common genetically characterized forms of limb-girdle muscular ...dystrophy with a wide range of phenotypic severity. We evaluated a consanguineous family with a clinical phenotype consistent with calpainopathy in whom conventional sequencing did not detect any mutations in the CAPN3 gene. Using whole exome sequencing paired with haplotype analysis, we identified a homozygous deep intronic single base pair deletion in CAPN3 (c.946-29delT). Familial segregation studies were consistent with recessive inheritance. Immunoblotting of muscle tissue from the patient showed complete absence of calpain 3. In silico analysis predicted the deletion to disrupt the branch point and subsequently alter splicing of exon 7. Studies of patient fibroblasts and muscle tissue confirmed altered splicing, resulting in an inclusion of a 389-bp intronic sequence upstream of exon 7, originating from a cryptic splice acceptor site in intron 6. This out-of-frame insertion results in a premature stop codon, leading to an apparent absence of protein likely due to degradation of the transcript via nonsense-mediated decay. We then designed phosphorodiamidate morpholino oligomers (PMOs) as splice modulators to block the new splice acceptor site. This approach successfully prevented the aberrant splicing - reverting the majority of the splice to the wildtype transcript. These results confirm the pathogenicity of this novel deep intronic mutation and provide a mutation-specific therapeutic strategy. Thus, deep intronic mutations in CAPN3 may be pathogenic and should be considered in the appropriate clinical setting. The identification of mutations which may be missed by traditional Sanger sequencing is essential as they may be excellent targets for individualized therapeutic strategies using RNA-directed splice modulation.
OBJECTIVETo better characterize adult myotubularin 1 (MTM1)–related myopathy carriers and recommend a phenotypic classification.
METHODSThis cohort study was performed at the NIH Clinical Center. ...Participants were required to carry a confirmed MTM1 mutation and were recruited via the Congenital Muscle Disease International Registry (n = 8), a traveling local clinic of the Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, NIH and Cure CMD (n = 1), and direct physician referral (n = 1). Neuromuscular examinations, muscle MRI, dynamic breathing MRI, cardiac MRI, pulmonary function tests (PFTs), physical therapy assessments including the Motor Function Measure 32 (MFM-32) scale, and X chromosome inactivation (XCI) studies were performed.
RESULTSPhenotypic categories were proposed based on ambulatory status and muscle weakness. Carriers were categorized as severe (nonambulatory; n = 1), moderate (minimal independent ambulation/assisted ambulation; n = 3), mild (independent ambulation but with evidence of muscle weakness; n = 4), and nonmanifesting (no evidence of muscle weakness; n = 2). Carriers with more severe muscle weakness exhibited greater degrees of respiratory insufficiency and abnormal signal on muscle imaging. Skeletal asymmetries were evident in both manifesting and nonmanifesting carriers. Skewed XCI did not explain phenotypic severity.
CONCLUSIONThis work illustrates the phenotypic range of MTM1-related myopathy carriers in adulthood and recommends a phenotypic classification. This classification, defined by ambulatory status and muscle weakness, is supported by muscle MRI, PFT, and MFM-32 scale composite score findings, which may serve as markers of disease progression and outcome measures in future gene therapy or other clinical trials.
To accurately categorize the phenotypes of individuals with collagen VI-related dystrophies (COL6-RDs) during the first years of life to predict long-term motor function and pulmonary function, to ...provide phenotype-specific anticipatory care, and to improve clinical trial readiness.
This retrospective, multicenter, international study analyzed the relationship of long-term motor and pulmonary function with the initial maximal motor ability achieved in individuals with COL6-RD.
We studied 119 patients with COL6-RD from Spain (n = 54) and the United States (n = 65). The early maximal motor milestones of ability to rise from the floor unassisted and ability to climb 4 steps without holding onto a railing demonstrated reliability in distinguishing between 3 COL6-RD phenotypic subgroups: (1) Ullrich congenital muscular dystrophy, (2) intermediate COL6-RD, and (3) Bethlem myopathy. Long-term motor function and pulmonary function are strongly correlated with the maximal motor ability achieved during the first years of life. Maximal motor capacity can predict other disease-relevant events such as the age at loss of ambulation and the need for the initiation of nocturnal noninvasive ventilation.
This work proposes a prospective phenotypic classification for COL6-RDs that will enable an accurate prediction of a patient's COL6-RD phenotype during the first years of life. The ability to establish a patient's COL6-RD phenotypic classification early will enable a more accurate prognosis of future motor and pulmonary function, thus improving anticipatory clinical care, and it will be instrumental in aiding the design of future clinical trials by allowing early stratification of trial cohorts.
•Cohort of 10 patients with ANO5 gene mutation with no cardiac symptoms reported.•Muscle MRI, neurological testing and cardiac imaging were performed.•Muscle MRI showed increased T1 signal in the ...posterior thigh and lower leg.•Cardiac imaging showed aortic root dilation & ventricular dilation in some patients.•Cardiac MRI showed cardiac fibrosis on late enhancement which is a novel finding.
Patients with bi-allelic loss-of-function mutations in the gene ANO5 most commonly present with muscular dystrophy. In some studies, patients with ANO5-related dystrophy (ANO5-RD) had evidence of mild cardiac abnormalities; however, cardiac magnetic resonance imaging (MRI) has not been used for myocardial characterization. Ten patients with genetically confirmed ANO5-RD were enrolled in a phenotyping study to better characterize cardiac involvement. Evaluations included medical history, neurological examination and cardiac evaluations (electrocardiogram, echocardiogram and cardiac MRI). All patients were clinically asymptomatic from a cardiac perspective. Muscle MRI was consistent with previous studies of ANO5-RD with increased T1 signal in the posterior and medial compartments of the upper leg and the posterior compartment of the lower leg. Cardiac studies using echocardiography and cardiac MRI revealed dilation of the aortic root and thickening of the aortic valve without significant stenosis in 3/10 patients. There was evidence of abnormal late gadolinium enhancement (LGE) on cardiac MRI in 2/10 patients. In ANO5-RD, the development of cardiac fibrosis, edema or inflammation as demonstrated by LGE has not yet been reported. Cardiac MRI can characterize cardiac tissue and may detect subtle changes before they appear on echocardiography, with potential prognostic implications.
Omigapil is a small molecule which inhibits the GAPDH-Siah1-mediated apoptosis pathway. Apoptosis is a pathomechanism underlying the congenital muscular dystrophy subtypes LAMA2-related dystrophy ...(LAMA2-RD) and COL6-related dystrophy (COL6-RD). Studies of omigapil in the (dyw/dyw) LAMA2-RD mouse model demonstrated improved survival, and studies in the (dy2J/dy2J) LAMA2-RD mouse model and the (Col6a1-/-) COL6-RD mouse model demonstrated decreased apoptosis.Background and ObjectivesOmigapil is a small molecule which inhibits the GAPDH-Siah1-mediated apoptosis pathway. Apoptosis is a pathomechanism underlying the congenital muscular dystrophy subtypes LAMA2-related dystrophy (LAMA2-RD) and COL6-related dystrophy (COL6-RD). Studies of omigapil in the (dyw/dyw) LAMA2-RD mouse model demonstrated improved survival, and studies in the (dy2J/dy2J) LAMA2-RD mouse model and the (Col6a1-/-) COL6-RD mouse model demonstrated decreased apoptosis.A phase 1 open-label, sequential group, ascending oral dose, cohort study of omigapil in patients with LAMA2-RD or COL6-RD ages 5-16 years was performed (1) to establish the pharmacokinetic (PK) profile of omigapil at a range of doses, (2) to evaluate the safety and tolerability of omigapil at a range of doses, and (3) to establish the feasibility of conducting disease-relevant clinical assessments. Patients were enrolled in cohorts of size 4, with each patient receiving 4 weeks of vehicle run-in and 12 weeks of study drug (at daily doses ranging from 0.02 to 0.08 mg/kg). PK data from each cohort were analyzed before each subsequent dosing cohort was enrolled. A novel, adaptive dose-finding method (stochastic approximation with virtual observation recursion) was used to allow for dose escalation/reduction between cohorts based on PK data.MethodsA phase 1 open-label, sequential group, ascending oral dose, cohort study of omigapil in patients with LAMA2-RD or COL6-RD ages 5-16 years was performed (1) to establish the pharmacokinetic (PK) profile of omigapil at a range of doses, (2) to evaluate the safety and tolerability of omigapil at a range of doses, and (3) to establish the feasibility of conducting disease-relevant clinical assessments. Patients were enrolled in cohorts of size 4, with each patient receiving 4 weeks of vehicle run-in and 12 weeks of study drug (at daily doses ranging from 0.02 to 0.08 mg/kg). PK data from each cohort were analyzed before each subsequent dosing cohort was enrolled. A novel, adaptive dose-finding method (stochastic approximation with virtual observation recursion) was used to allow for dose escalation/reduction between cohorts based on PK data.Twenty patients were enrolled at the NIH (LAMA2-RD: N = 10; COL6-RD: N = 10). Slightly greater than dose-proportional increases in systemic exposure to omigapil were seen at doses 0.02-0.08 mg/kg/d. The dose which achieved patient exposure within the pre-established target area under the plasma concentration-vs-time curve (AUC0-24h) range was 0.06 mg/kg/d. In general, omigapil was safe and well tolerated. No consistent changes were seen in the disease-relevant clinical assessments during the duration of the study.ResultsTwenty patients were enrolled at the NIH (LAMA2-RD: N = 10; COL6-RD: N = 10). Slightly greater than dose-proportional increases in systemic exposure to omigapil were seen at doses 0.02-0.08 mg/kg/d. The dose which achieved patient exposure within the pre-established target area under the plasma concentration-vs-time curve (AUC0-24h) range was 0.06 mg/kg/d. In general, omigapil was safe and well tolerated. No consistent changes were seen in the disease-relevant clinical assessments during the duration of the study.This study represents the thus far only clinical trial of a therapeutic small molecule for LAMA2-RD and COL6-RD, completed with an adaptive trial design to arrive at dose adjustments. The trial met its primary end point and established that the PK profile of omigapil is suitable for further development in pediatric patients with LAMA2-RD or COL6-RD, the most common forms of congenital muscular dystrophy. While within the short duration of the study disease-relevant clinical assessments did not demonstrate significant changes, this study establishes the feasibility of performing interventional clinical trials in these rare disease patient populations.DiscussionThis study represents the thus far only clinical trial of a therapeutic small molecule for LAMA2-RD and COL6-RD, completed with an adaptive trial design to arrive at dose adjustments. The trial met its primary end point and established that the PK profile of omigapil is suitable for further development in pediatric patients with LAMA2-RD or COL6-RD, the most common forms of congenital muscular dystrophy. While within the short duration of the study disease-relevant clinical assessments did not demonstrate significant changes, this study establishes the feasibility of performing interventional clinical trials in these rare disease patient populations.This study provides Class IV evidence of omigapil in a dose-finding phase 1 study.Classification of EvidenceThis study provides Class IV evidence of omigapil in a dose-finding phase 1 study.Clinical Trials NCT01805024.Trial Registration InformationClinical Trials NCT01805024.
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