Disclosed are compositions and methods for aiding in the diagnosis of congenital muscular dystrophy associated with in-frame deletion in the laminin-2 .alpha.2 polypeptide chain in an individual. In a preferred diagnostic method embodiment, an experimental muscle tissue sample is provided from the individual and treated if necessary to render components available for antibody binding. The components of the sample are then separated on the basis of molecular weight. The separated protein components are then transferred to a solid support while maintaining the relative positions established in separation step. The transferred components are then stained with an affinity reagent which is known to bind to a C-terminal domain of the laminin-2 .alpha.2 polypeptide chain. Individual afflicted with congenital muscular dystrophy associated with in-frame deletion in the laminin-2 .alpha.2 polypeptide chain on the basis of positive staining in combination with reduced molecular weight of the laminin-2 .alpha.2 polypeptide chain relative to the wild-type laminin-2 .alpha.2 polypeptide chain. A preferred composition is a nucleic acid probe for the detection of merosin deletion-type congenital muscular dystrophy. The preferred nucleic acid probe is characterized by the ability to bind specifically to a mutant merosin nucleic acid sequence, the mutant merosin nucleic acid sequence comprising a T to C substitution at position 3973 +2 of the consensus donor splice site of exon 25.