X inactivation patterns in two syndromes with probable X‐linked dominant, male lethal inheritance

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Abstract
For Incontinentia pigmenti Bloch‐Sulzberger (IP) and Aicardi syndrome, an X‐linked dominant transmission with lethality in hemizygous males has been proposed. The typical transition from inflammation to verrucous hypertrophy and hyperpigmented skin areas in IP suggests a gradual replacement of defective cells by normal cells. This would imply a preferential inactivation of the X chromosome carrying the IP gene with a proliferative advantage of this cell population. We have confirmed this hypothesis by demonstrating that the same X chromosome is preferentially active in fibroblasts grown from normal and hyperpigmented skin of an affected girl. In contrast, X inactivation was random in a girl with Aicardi syndrome.