Apparent non-penetrance for dystopia in Waardenburg syndrome type I, with some hints on the diagnosis of dystopia canthorum.

Two large pedigrees with Waardenburg syndrome type I (W--I), i.e. with dystopia canthorum and blepharophimosis, are described to show both the variable expressivity of dystopia canthorum, which may be confused with non-penetrance of this sign, and the possibility to firmly diagnosis it with the new biometric index W, which differentiates a dystopic from a non-dystopic or a non-apparent dystopic subject, the latter within a defined biometric range. A general discussion of the relative value of blepharophimosis and dystopia canthorum as diagnostic features in W--I is presented, to conclude on the greater value of dystopia canthorum, which can be identified with confidence in more than 96% of carriers. Empirical probabilities are given for dystopia canthorum and blepharophimosis in the general populations, based on data from the world literature, useful for all ethnic groups.