The clinical spectrum of CASQ1-related myopathy.

OBJECTIVE: To identify and characterize patients with calsequestrin 1 (CASQ1)-related myopathy. METHODS: Patients selected according to histopathologic features underwent CASQ1 genetic screening. CASQ1-mutated patients were clinically evaluated and underwent muscle MRI. Vacuole morphology and vacuolated fiber type were characterized. RESULTS: Twenty-two CASQ1-mutated patients (12 families) were identified, 21 sharing the previously described founder mutation (p.Asp244Gly) and 1 with the p.Gly103Asp mutation. Patients usually presented in the sixth decade with exercise intolerance and myalgias and later developed mild to moderate, slowly progressive proximal weakness with quadriceps atrophy and scapular winging. Muscle MRI (n = 11) showed a recurrent fibrofatty substitution pattern. Three patients presented subclinical cardiac abnormalities. Muscle histopathology in patients with p.Asp244Gly showed vacuoles in type II fibers appearing empty in hematoxylin-eosin, Gomori, and nicotinamide adenine dinucleotide (NADH) tetrazolium reductase stains but strongly positive for sarcoplasmic reticulum proteins. The muscle histopathology of p.Gly103Asp mutation was different, showing also NADH-positive accumulation consistent with tubular aggregates. CONCLUSIONS: We report the clinical and molecular details of the largest cohort of CASQ1-mutated patients. A possible heart involvement is presented, further expanding the phenotype of the disease. One mutation is common due to a founder effect, but other mutations are possible. Because of a paucity of symptoms, it is likely that CASQ1 mutations may remain undiagnosed if a muscle biopsy is not performed.

SPP1 genotype and glucocorticoid treatment modify osteopontin expression in Duchenne muscular dystrophy cells.

Glucocorticoids are beneficial in Duchenne muscular dystrophy (DMD). Osteopontin (OPN), the protein product of SPP1, plays a role in DMD pathology modulating muscle inflammation and regeneration. A polymorphism in the SPP1 promoter (rs28357094) has been recognized as a genetic modifier of DMD, and there is evidence suggesting that it modifies response to glucocorticoid treatment. The effect of the glucocorticoid deflazacort on SPP1 mRNA and protein expression was investigated in DMD primary human myoblasts and differentiated myotubes with defined rs28357094 genotype (TT versus TG). Both healthy and DMD myoblasts/myotubes abundantly express OPN. In immunoblot, OPN was detected as a doublet of 55 and 50 kDa bands, with a shift towards the lighter isoform in the transition from myoblasts to myotubes and to mature muscle. A significant increase in OPN expression was observed in DMD myotubes carrying the TG compared to the TT genotype at rs28357094. Deflazacort treatment led to a significant increase of OPN only in myotubes carrying the TG genotype, leading to OPN overexpression. Our study shows a strong effect of the rs28357094 G allele in increasing OPN expression in the presence of deflazacort, and adds to the evidence that rs28357094 polymorphism may predict response to glucocorticoids in DMD.

Cardiomyopathy in patients with POMT1-related congenital and limb-girdle muscular dystrophy.

Protein-o-mannosyl transferase 1 (POMT1) is a glycosyltransferase involved in α-dystroglycan (α-DG) glycosylation. Clinical phenotype in POMT1-mutated patients ranges from congenital muscular dystrophy (CMD) with structural brain abnormalities, to limb-girdle muscular dystrophy (LGMD) with microcephaly and mental retardation, to mild LGMD. No cardiac involvement has until now been reported in POMT1-mutated patients. We report three patients who harbored compound heterozygous POMT1 mutations and showed left ventricular (LV) dilation and/or decrease in myocardial contractile force: two had a LGMD phenotype with a normal or close-to-normal cognitive profile and one had CMD with mental retardation and normal brain MRI. Reduced or absent α-DG immunolabeling in muscle biopsies were identified in all three patients. Bioinformatic tools were used to study the potential effect of POMT1-detected mutations. All the detected POMT1 mutations were predicted in silico to interfere with protein folding and/or glycosyltransferase function. The report on the patients described here has widened the clinical spectrum associated with POMT1 mutations to include cardiomyopathy. The functional impact of known and novel POMT1 mutations was predicted with a bioinformatics approach, and results were compared with previous in vitro studies of protein-o-mannosylase function.

TGFBR2 but not SPP1 genotype modulates osteopontin expression in Duchenne muscular dystrophy muscle.

A polymorphism (rs28357094) in the promoter region of the SPP1 gene coding for osteopontin (OPN) is a strong determinant of disease severity in Duchenne muscular dystrophy (DMD). The rare G allele of rs28357094 alters gene promoter function and reduces mRNA expression in transfected HeLa cells. To dissect the molecular mechanisms of increased disease severity associated with the G allele, we characterized SPP1 mRNA and protein in DMD muscle biopsies of patients with defined rs28357094 genotype. We did not find significant differences in osteopontin mRNA or protein expression between patients carrying the T (ancestral allele) or TG/GG genotypes at rs28357094. The G allele was significantly associated with reduced CD4(+) and CD68(+) cells on patient muscle biopsy. We also quantified transforming growth factor-ß (TGFB) and TGFB receptor-2 (TGFBR2) mRNA in DMD muscle biopsies, given the ability of TGFB and TGFBR2 to activate SPP1 promoter region and their role in DMD pathogenesis. The amount of TGFB and TGFBR2 mRNA did not predict the amount of SPP1 mRNA or protein, while a polymorphism in the TGFBR2 gene (rs4522809) was found to be a strong predictor of SPP1 mRNA level. Our findings suggest that OPN mediates inflammatory changes in DMD and that TGFB signalling has a role in the complex regulation of osteopontin expression.

Clinical and molecular characterization of limb-girdle muscular dystrophy due to LAMA2 mutations.

INTRODUCTION: In this study we describe the clinical and molecular characteristics of limb-girdle muscular dystrophy (LGMD) due to LAMA2 mutations. METHODS: Five patients clinically diagnosed with LGMD and showing brain white matter hyperintensities on MRI were evaluated using laminin α2 genetic and protein testing. RESULTS: The patients had slowly progressive, mild muscular dystrophy with various degrees of CNS involvement. Epilepsy was observed in 2, and subtle symptoms of CNS involvement (mild deficit in executive functions and low IQ scores) were noted in 3 patients. Novel LAMA2 mutations were identified in all patients. The amount of laminin α2 protein in the muscle biopsies ranged from trace to about 50% compared with controls. CONCLUSIONS: This study represents the largest series of LGMD laminin α2-deficient patients and expands the clinical phenotype associated with LAMA2 mutations. The findings suggest that brain MRI could be included in the diagnostic work-up of patients with undiagnosed LGMD.

Biochemical and ultrastructural evidence of endoplasmic reticulum stress in LGMD2I.

Limb girdle muscular dystrophy type 2I (LGMD2I) is due to mutations in the fukutin-related protein gene (FKRP), encoding a putative glycosyltransferase involved in alpha-dystroglycan processing. To further characterize the molecular pathogenesis of LGMD2I, we conducted a histological, immunohistochemical, ultrastructural and molecular analysis of ten muscle biopsies from patients with molecularly diagnosed LGMD2I. Hypoglycosylation of alpha-dystroglycan was observed in all FKRP-mutated patients. Muscle histopathology was consistent with either severe muscular dystrophy or myopathy with a mild inflammatory response consisting of up-regulation of class I major histocompatibility complex in skeletal muscle fibers and small foci of mononuclear cells. At the ultrastructural level, muscle fibers showed focal thinning of basal lamina and swollen endoplasmic reticulum cisternae with membrane re-arrangement. The pathways of the unfolded protein response (UPR; glucose-regulated protein 78 and CHOP) were significantly activated in LGMD2I muscle tissue. Our data suggest that the UPR response is activated in LGMD2I muscle biopsies, and the observed histopathological and ultrastructural alterations may be related to sarcoplasmic structures involved in FKRP and alpha-dystroglycan metabolism and malfunctioning.

MYH7 gene mutation in myosin storage myopathy and scapulo-peroneal myopathy.

In order to characterize, at the clinical, molecular and imaging level, myopathies due to MYH7 gene mutations, MYH7 gene analysis was conducted by RT-PCR/SSCP/sequencing in two patients diagnosed with myosin storage myopathy and 17 patients diagnosed with scapulo-peroneal myopathy of unknown etiology. MYH7 gene studies revealed the 5533C>T mutation (Arg1845Trp) in both myosin storage myopathy and in 2 of the 17 scapulo-peroneal patients studied. 5533C>T segregation analysis in the mutation carrier families identified 11 additional patients. The clinical spectrum in our cohort of patients included asymptomatic hyperCKemia, scapulo-peroneal myopathy and proximal and distal myopathy with muscle hypertrophy. Muscle MRI identified a unique pattern in the posterior compartment of the thigh, characterized by early involvement of the biceps femoris and semimembranosus, with relative sparing of the semitendinosus. Muscle biopsy revealed hyaline bodies in only half of biopsied patients (2/4). In conclusion, phenotypic and histopathological variability may underlie MYH7 gene mutation and the absence of hyaline bodies in muscle biopsies does not rule out MYH7 gene mutations.

Clinical and molecular characterization of patients with limb-girdle muscular dystrophy type 2I.

BACKGROUND: Limb-girdle muscular dystrophy type 2I is caused by mutations in the fukutin-related protein gene (FKRP). FKRP encodes a putative glycosyltransferase protein that is involved in alpha-dystroglycan glycosylation. OBJECTIVES: To identify patients with limb-girdle muscular dystrophy type 2I and to derive genotype-phenotype correlations. DESIGN: Two hundred fourteen patients who showed muscle histopathologic features consistent with muscular dystrophy or myopathy of unknown etiology were studied. The entire 1.5-kilobase FKRP coding sequence from patient DNA was analyzed using denaturing high-performance liquid chromatography of overlapping polymerase chain reaction products, followed by direct sequencing of heteroduplexes. RESULTS: Thirteen patients with limb-girdle muscular dystrophy type 2I (6% of all patients tested) were identified by FKRP mutation analysis, and 7 additional patients were identified by family screening. Six missense mutations (1 novel) were identified. The 826C>A nucleotide change was a common mutation, present in 35% of the mutated chromosomes. Clinical presentations included asymptomatic hyperCKemia, severe early-onset muscular dystrophy, and mild late-onset muscular dystrophy. Dilated cardiomyopathy and ventilatory impairment were frequent features. Significant intrafamilial and interfamilial clinical variability was observed. CONCLUSIONS: FKRP mutations are a frequent cause of limb-girdle muscular dystrophies. The degree of respiratory and cardiac insufficiency in patients did not correlate with the severity of muscle involvement. The finding of 2 asymptomatic patients with FKRP mutations suggests that modulating factors may ameliorate the clinical phenotype.

Co-segregation of LMNA and PMP22 gene mutations in the same family.

We report here clinical, electrophysiological, and molecular findings in a family affected with two inherited genetic diseases: limb girdle muscular dystrophy type 1B (LGMD1B) and hereditary neuropathy with liability to pressure palsies (HNPP). Members of the family carry a novel missense mutation in the LMNA gene and a nonsense mutation in the PMP22 gene. Interestingly, the double LMNA/PMP22 mutations carriers showed clinical features more severe than usually seen in HNPP, and electrophysiological findings suggesting an axonal loss in addition to a typical myelinopathy. This study provides further insights into the relevance of lamin A/C in muscle and nerve.