Congenital muscular dystrophy with laminin α2 chain deficiency: Identification of a new intermediate phenotype and correlation of clinical findings to muscle immunohistochemistry

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Abstract
The laminins comprise of a family of heterotrimeric proteins of the extracellular matrix. The cross-shaped proteins consist of a heavy α-chain and two light chains, called β and γ. Each group of chains, classified on their sequence identity and domain organization, include different isoforms. A deficiency of the α2 chain of laminin-2, previously termed merosin or M component, was shown to be responsible for one form of congenital muscular dystrophy (CMD). We investigated muscle biopsies of 20 patients with the clinical diagnosis of CMD and histological evidence of muscular dystrophy for the expression of different laminin chains. Patients with evidence of pachygyria/lissencephaly of the CNS were excluded from this series. The immunohistochemical analysis was correlated to clinical findings and MRI data of the brain. Of 20 patients, 11 (55%) revealed complete or near-complete deficiency of the α2 chain in their skeletal muscle specimens. So far none of these patients became ambulant. Of 20 patients 2 showed partial but clear-cut α2 chain-deficiency. These two patients became ambulant at 18 months and 3 years. All 13 patients with complete or partial α2 chain-deficiency demonstrated cerebral white matter changes on MRI. In contrast, 6/7 CMD patients with normal α2 chain expression became ambulant and none of the 6/7 tested showed evidence of cerebral abnormal T2 sequence signal of the myelin on MRI.

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