Expression profiling of muscles from Fukuyama-type congenital muscular dystrophy and laminin-α2 deficient congenital muscular dystrophy; is congenital muscular dystrophy a primary fibrotic disease?

Fukuyama-type congenital muscular dystrophy (FCMD) and laminin-α2 deficient congenital muscular dystrophy (MDC1A) are congenital muscular dystrophies (CMDs) and they both are categorized into the same clinical entity of muscular dystrophy as Duchenne muscular dystrophy (DMD). All three disorders share a common etiologic defect in the dystrophin–glycoprotein complex, which connects muscle structural proteins with the extracellular basement membrane. To investigate the pathophysiology of these CMDs, we generated microarray gene expression profiles of skeletal muscle from patients in various clinical stages. Despite diverse pathological changes, the correlation coefficient of overall gene expression among these samples was considerably high. We performed a multi-dimensional statistical analysis, the Distillation, to extract determinant genes that distinguish CMD muscle from normal controls. Up-regulated genes were primarily extracellular matrix (ECM) components, whereas down-regulated genes included structural components of mature muscle. These observations reflect active interstitial fibrosis with less active regeneration of muscle cell components in the CMDs, characteristics that are clearly distinct from those of DMD. Although the severity of fibrosis varied among the specimens tested, ECM gene expression was consistently high without substantial changes through the clinical course. Further, in situ hybridization showed more prominent ECM gene expression on muscle cells than on interstitial tissue cells, suggesting that ECM components are induced by regeneration process rather than by ‘dystrophy.’ These data imply that the etiology of FCMD and MDC1A differs from that of the chronic phase of classical muscular dystrophy, and the major pathophysiologic change in CMDs might instead result from primary active fibrosis.