Congenital Muscular Dystrophy 1A Research Articles

Genotype–phenotype correlation in a large population of muscular dystrophy patients with LAMA2 mutations

Merosin deficient congenital muscular dystrophy 1A (MDC1A) results from mutations in the LAMA2 gene. We report 51 patients with MDC1A and examine the relationship between degree of merosin expression, genotype and clinical features. Thirty-three patients had absence of merosin and 13 showed some residual merosin. Compared to the residual merosin group, patients with absent merosin had an earlier presentation (<7 days) ( P = 0.0073), were more likely to lack independent ambulation ( P = 0.0215), or require enteral feeding ( P = 0.0099) and ventilatory support ( P = 0.0354). We identified 33 novel LAMA2 mutations; these were distributed throughout the gene in patients with absent merosin, with minor clusters in exon 27, 14, 25 and 26 (55% of mutations). Patients with residual merosin often carried at least one splice site mutation and less frequently frameshift mutations. This large study identified novel LAMA2 mutations and highlights the role of immunohistochemical studies for merosin status in predicting clinical severity of MDC1A.

A Laminin-2, Dystroglycan, Utrophin Axis Is Required for Compartmentalization and Elongation of Myelin Segments

Animal and plant cells compartmentalize to perform morphogenetic functions. Compartmentalization of myelin-forming Schwann cells may favor elongation of myelin segments to the size required for efficient conduction of nerve impulses. Compartments in myelinated fibers were described by Ramón y Cajal and depend on periaxin, mutated in the hereditary neuropathy Charcot-Marie-Tooth disease type 4F (Charcot-Marie-Tooth 4F). Lack of periaxin in mice causes loss of compartments, formation of short myelin segments (internodes) and reduced nerve conduction velocity. How compartments are formed and maintained, and their relevance to human neuropathies is largely unknown. Here we show that formation of compartments around myelin is driven by the actin cytoskeleton, and maintained by actin and tubulin fences through linkage to the dystroglycan complex. Compartmentalization and establishment of correct internodal length requires the presence of glycosylated dystroglycan, utrophin and extracellular laminin-2/211. A neuropathic patient with reduced internodal length and nerve conduction velocity because of absence of laminin-2/211 (congenital muscular dystrophy 1A) also shows abnormal compartmentalization. These data link formation of compartments through a laminin2, dystroglycan, utrophin, actin axis to internodal length, and provide a common pathogenetic mechanism for two inherited human neuropathies. Other cell types may exploit dystroglycan complexes in similar fashions to create barriers and compartments.

A single point mutation in the LN domain of LAMA2 causes muscular dystrophy and peripheral amyelination

Mutations in the gene encoding the basal lamina (BL) component laminin alpha2 (LAMA2) cause merosin-deficient congenital muscular dystrophy 1A (MDC1A), a complex disorder that includes hypomyelination and myodegeneration. In dystrophia muscularis (dy) mice bearing Lama2 mutations, myofibers and Schwann cells fail to assemble stable BLs, which are thought to be crucial for myofiber survival and Schwann cell differentiation. Here, we describe defects in a new allele of Lama2 in mice, nmf417, in which a point mutation substitutes Arg for Cys79 at a universally conserved CxxC motif in the laminin N-terminal (LN) domain; this domain mediates laminin-laminin interactions. nmf417 homozygosity caused progressive myodegeneration and severe peripheral amyelination in nerve roots, similar to previous Lama2 mutations, but without the pervasive BL thinning previously associated with the disorder. In direct contrast to the previously characterized dy and dy2J alleles, nmf417 homozygous myofibers frequently had thickened BLs. Severe amyelination in nmf417-mutant nerve roots suggested complete laminin 2 inactivation for Schwann cells, although myelinated fibers had normal BLs. The results reveal crucial roles for the LN domain CxxC motif in both nerve and muscle, but challenge expected relationships between LN-domain function, Ln2 activity and BL stability. The nmf417 mutation provides a defined animal model in which to investigate mechanisms and treatments for moderate forms of MDC1A.

Diagnosis of congenital muscular dystrophy and clinical significance of merosin expression

The congenital muscular dystrophies (CMD) are a clinically and genetically heterogeneous group of neuromuscular disorders with progressive muscle wasting and weakness that begin during neonatal or early infantile period. To study the clinical diagnosis, immunohistochemical feature and follow-up information of CMD, data of 8 cases with CMD were analyzed. Immunohistochemical features of biopsied muscle specimens were summarized and analyzed by using anti-laminin alpha2 (merosin), anti alpha-dystroglycan (alpha-DG) and anti beta-dystroglycan (beta-DG) antibodies. These patients mostly presented at birth or during the first six months of life with muscle weakness, hypotonia, contractures, and feeding difficulty or respiratory dysfunction. Hematoxylin-eosin staining of skeletal muscle specimens from these patients showed typical characteristics of CMD. Differences in fiber size, with predominantly small and round fibers, and dense connective tissue infiltration were seen. Four of the 8 patients were merosin-stain negative, which might be due to primary merosin deficiency. T2-weighted magnetic resonance imaging of the brain shows abnormalities of the white matter. Four cases were merosin-stain positive, and two of them also had hypoglycosylation of alpha-dystroglycan. Two patients had mental retardation. One of them had optic nerve atrophy and abnormal brain structure. Two types of CMD were present in our group. Merosin-deficient congenital muscular dystrophy (congenital muscular dystrophy 1A, MDC1A) was more common, accompanied by abnormalities of the white matter. "Alpha-dystroglycanopathy" could be seen in merosin-positive cases.