Mild Congenital Muscular Dystrophy in Two Patients with an Internally Deleted Laminin 2-Chain

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Abstract
Congenital muscular dystrophy (CMD) is a group of clinically and genetically heterogeneous disorders inherited in an autosomal recessive mode. The α2-chain of laminin-2 (previously called merosin) has been shown by immunohistochemical and genetic analyses to be implicated in the pathogenesis of the “classic” form of CMD. In the “merosin-deficient” subgroup, which represents about half of the cases, more definite evidence of the involvement of the laminin α2-chain has recently been reported with the identification of mutations in the gene encoding the α2-chain of laminin 2 (LAMA2) in CMD patients. Here we report on two siblings from a consanguineous family expressing an internally deleted laminin α2-chain as a result of a splice site mutation in the LAMA2 gene which causes the splicing of exon 25. The predicted protein lacks 63 amino acids in domain IVa which forms a globular structure on the short arm of the α2-chain. Interestingly, these patients appear mildly affected compared to others who completely lack this protein. This situation presents a striking analogy with Becker muscular dystrophy, where in-frame deletions in the dystrophin gene result in the expression of a semi-functional protein and lead to a mild phenotype.