Deletion of the paired alpha 5(IV) and alpha 6(IV) collagen genes in inherited smooth muscle tumors.

The gene encoding alpha 6(IV) collagen, COL4A6, was identified on the human X chromosome in a head-to-head arrangement and within 452 base pairs of the alpha 5(IV) collagen gene, COL4A5. In earlier studies, intragenic deletions of COL4A5 were detected in a subset of patients with Alport syndrome (AS), a hereditary defect of basement membranes. In some families, AS cosegregates with diffuse leiomyomatosis (DL), a benign smooth muscle tumor diathesis. Here it is shown that patients with AS-DL harbor deletions that disrupt both COL4A5 and COL4A6. Thus, type IV collagen may regulate smooth muscle differentiation and morphogenesis.