LAMININ ALPHA-2 MUSCULAR-DYSTROPHY - GENOTYPE PHENOTYPE STUDIES OF 22PATIENTS/

Objective: To determine the number of primary laminin alpha 2 gene mut ations and to conduct genotype/phenotype correlation in a cohort of la minin alpha 2-deficient congenital muscular dystrophy patients. Backgr ound: Congenital muscular dystrophies (CMD) are a heterogeneous group of muscle disorders characterized by early onset muscular dystrophy an d a variable involvement of the CNS. Laminin alpha 2 deficiency has be en reported in about 40 to 50% of cases of the occidental, classic typ e 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 t o interact with myofiber membrane receptor, such as integrins, and pos sibly dystrophin-associated glycoproteins.(3,4) Methods: Seventy-five CMD patients were tested for laminin alpha 2 expression by immunofluor escence and immunoblot. The entire 10 kb laminin alpha 2 coding sequen ce of 22 completely laminin alpha 2-deficient patients was screened fo r causative mutations by reverse transcription (RT)-PCR/single strand conformational polymorphisms (SSCP) analysis and protein truncation te st (PTT) analysis followed by automatic sequencing of patient cDNA. Cl inical data from the laminin alpha 2-deficient patients were collected . Results: Thirty laminin alpha 2-negative patients were identified (4 0% of CMD patients tested) and 22 of them were screened for laminin al pha 2 mutations. Clinical features of laminin cra-deficient patients w ere 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% (21/2 2) of the patients studied. SSCP analysis detected laminin alpha 2 gen e mutations in about 50% of the mutant chromosomes; PTT successfully i dentified 75% of the mutations. A two base pair deletion mutation at p osition 2,096-2,097 bp was present in 23% of the patients analyzed. Co nclusions: Our data suggest that the large majority of laminin alpha 2 -deficient patients show laminin alpha 2 gene mutations.