[Alport's syndrome: apropos of 2 families].

Two families with Alport's syndrome are presented. In the first family, the mode of inheritance is X-linked dominant; the molecular defect involves the alpha 5 chain of type IV collagen, absent from the glomerular and epidermal basal membrane in hemizygous males. In the other family, the transmission is autosomal recessive and the defect involves alpha 3(IV), absent from the glomerular basement membrane in homozygotes but alpha 5(IV) is normally present in the epidermal basement membrane. The consequences of these data on diagnosis and genetic counseling are discussed.