Waardenburg syndrome--penetrance of major signs.

We have estimated that 83% of individuals carrying the gene for Waardenburg syndrome type I show penetrance of the gene as measured by dystopia canthorum. This is lower than previous estimates, which failed to consider the frequency of equivocal dystopia in the general population. The addition of three other major signs (hearing loss, white forelock, and premature graying of the hair or vitiligo) does not substantially increase the discrimination of gene carriers (85% versus 83%). We estimate that about 75% of the first-degree relatives of probands can be assigned as normal or a gene carrier on the basis of the four major signs.