A family with MA5A Syndrome in 4 generation is described. Identification of the mutation in the L1CAM gene makes it possible to diagnose heterozygous carriers or to exclude the risk of their reproduction and to detect prenatally affected hemizygous male foetuses. Adducted thumbs are a signal of the affection in hemizygotes.

        Key words: MA5A Syndrome, mutation in L1CAM gene, mental retardation, adducted thumbs