Laminin α2 muscular dystrophy -: Genotype/phenotype studies of 22 patients

Objective: To determine the number of primary laminin alpha 2 gene mutations and to conduct genotype/phenotype correlation in a cohort of laminin alpha 2-deficient congenital muscular dystrophy patients. Background: Congenital muscular dystrophies (CMD) are a heterogeneous group of muscle disorders characterized by early onset muscular dystrophy and a variable involvement of the CNS. Laminin alpha 2 deficiency has been reported in about 40 to 50% of cases of the occidental, classic type of CMD.(1,2) Laminin alpha 2 is a muscle specific isoform of laminin localized to the basal lamina of muscle fibers, where it is thought to interact with myofiber membrane receptor, such as integrins, and possibly dystrophin-associated glycoproteins.(3,4) Methods: Seventy-five CMD patients were tested for laminin alpha 2 expression by immunofluorescence and immunoblot. The entire 10 kb laminin alpha 2 coding sequence of 22 completely laminin alpha 2-deficient patients was screened for causative mutations by reverse transcription (RT)-PCR/single strand conformational polymorphisms (SSCP) analysis and protein truncation test (PTT) analysis followed by automatic sequencing of patient cDNA. Clinical data from the laminin alpha 2-deficient patients were collected. Results: Thirty laminin alpha 2-negative patients were identified (40% of CMD patients tested) and 22 of them were screened for laminin alpha 2 mutations. Clinical features of laminin cra-deficient patients were similar, with severe floppiness at birth, delay in achievement of motor milestones, and MRI findings of white matter changes with normal intelligence. Loss-of-function mutations were identified in 95% (21/22) of the patients studied. SSCP analysis detected laminin alpha 2 gene mutations in about 50% of the mutant chromosomes; PTT successfully identified 75% of the mutations. A two base pair deletion mutation at position 2,096-2,097 bp was present in 23% of the patients analyzed. Conclusions: Our data suggest that the large majority of laminin alpha 2-deficient patients show laminin alpha 2 gene mutations.