ABSTRACT
OBJECTIVE: Autosomal recessive limb girdle muscular dystrophies (LGMD type 2) are a clinically and genetically heterogeneous group of disorders, characterized by progressive involvement and wasting of limb girdle muscles. In order to describe the peculiar clinical features of LGMD2A (calpainopathy) and LGMD2B (dysferlinopathy), the most frequent forms of LGMD in European countries, we analysed and compared the phenotype and the clinical course in two relatively large groups of these patients. METHODS: We selected 22 patients with a molecular diagnosis of LGMD2A and 21 patients with LGMD2B and reported their clinical data collected from both clinical history and during periodical neuromuscular examinations: age and distribution of muscle involvement at onset, clinical functional score by the use of ten-point modified scale of Gardner-Medwin and Walton at onset and at last clinical examination, and the rate of disease progression. RESULTS: LGMD2A group included patients with different ages at onset (early-onset or late-onset), different phenotypes (upper girdle in Erb LGMD or lower girdle in Leyden-Moebius LGMD) and different disease progressions (rapid or slow course). LGMD2B patients differed for pattern of muscle involvement at onset (distal in Miyoshi dystrophy or proximal in Leyden-Moebius LGMD) but they had a rather homogeneous age at onset (in the second/third decade) and rate of disease progression. DISCUSSION: Our data show that besides the clinical differences within each group of patients, the two forms of LGMD present distinctive clinical features. The various phenotypes and courses can be attributed to specific pathogenetic mechanisms and might suggest differential therapeutic strategies.
Subject(s)
Disease Progression , Muscular Dystrophies, Limb-Girdle , Adolescent , Adult , Age of Onset , Child , Child, Preschool , Female , Humans , Male , Neurologic Examination , Phenotype , Retrospective Studies , Severity of Illness Index , Young AdultABSTRACT
BACKGROUND: The frequency of various limb-girdle muscular dystrophy (LGMD) molecular diagnoses has previously been investigated only in cohorts of patients presenting LGMD phenotype. METHODS: A total of 550 muscle biopsies underwent multiple protein screening (including calpain-3 functional assay) and extensive gene mutation analysis to examine the frequency of LGMD subtypes in patients with distinct clinical phenotypes (severe childhood-onset LGMD, adult-onset LGMD, distoproximal myopathy, and asymptomatic hyperCKemia). RESULTS: The percentage of molecularly ascertained cases directly relates with the degree of clinical involvement: 60% of total LGMD (77% of childhood-onset, 46% of adult-onset, 66% of distoproximal myopathy) and 14% of hyperCKemia. The higher number of molecular diagnoses in severe phenotypes might suggest that genes selected for our screening are those more frequently associated with severe LGMD, and that the hyperCKemia group includes heterogeneous diagnoses. The probability of obtaining a molecular diagnosis increases when a protein defect is found in a muscle biopsy: in such cases, we diagnosed 87% of LGMD and 76% of hyperCKemia. CONCLUSIONS: Diagnosing 77% of childhood-onset limb-girdle muscular dystrophy (LGMD) and 60% of total LGMD is an important result. The missing identification of gene mutations in about 40% of patients with typical LGMD phenotype suggests that unknown genetic or nongenetic etiologies are still to be recognized. Dysferlin, caveolin-3, and emerin protein defects invariably corresponded to primary disorders (100%), whereas a lower correlation was found for sarcoglycans (77%) and calpain-3 (84%). The different efficiency of genetic diagnosis after the identification of a protein defect in the various disorders is possibly due to different pathogenetic effects of mutations.
Subject(s)
Genetic Predisposition to Disease/genetics , Muscle Proteins/genetics , Muscular Dystrophies, Limb-Girdle/genetics , Mutation/genetics , Adult , Age of Onset , Calpain/genetics , Caveolin 3/genetics , Child , Cohort Studies , Creatine Kinase/metabolism , DNA Mutational Analysis , Dysferlin , Female , Gene Frequency/genetics , Genetic Testing , Genotype , Humans , Italy , Male , Membrane Proteins/genetics , Muscular Dystrophies, Limb-Girdle/metabolism , Muscular Dystrophies, Limb-Girdle/physiopathology , Nuclear Proteins/genetics , Phenotype , Sarcoglycans/geneticsABSTRACT
BACKGROUND: Limb girdle muscular dystrophy type 2A (LGMD2A) is characterised by wide variability in clinical features and rate of progression. Patients with two null mutations usually have a rapid course, but in the remaining cases (two missense mutations or compound heterozygote mutations) prognosis is uncertain. METHODS: We conducted what is to our knowledge the first systematic histopathological, biochemical and molecular investigation of 24 LGMD2A patients, subdivided according to rapid or slow disease progression, to determine if some parameters could correlate with disease progression. RESULTS: We found that muscle histopathology score and the extent of regenerating and degenerating fibres could be correlated with the rate of disease course when the biochemical and molecular data do not offer sufficient information. Comparison of clinical and muscle histopathological data between LGMD2A and four other types of LGMD (LGMD2B-E) also gave another important and novel result. We found that LGMD2A has significantly lower levels of dystrophic features (ie degenerating and regenerating fibres) and higher levels of chronic changes (ie lobulated fibres) compared with other LGMDs, particularly LGMD2B. These results might explain the observation that atrophic muscle involvement seems to be a clinical feature peculiar to LGMD2A patients. CONCLUSIONS: Distinguishing patterns of muscle histopathological changes in LGMD2A might reflect the effects of a disease-specific pathogenetic mechanism and provide clues complementary to genetic data.
