COL4A2 and cyst: While sequence analysis of patient IV:21, who has a large porencephalic cyst, excluded COL4A1 mutations, it identified a base pair change in exon 28 of COL4A2 (Fig. 1B) that is predicted to substitute a glycine residue of a Gly-X-Y repeat for aspartic acid (G702D) (Fig. 1C).