The Genetics of Incontinentia Pigmenti

The familial incidence of incontinentia pigmenti and its almost exclusive occurrence in females have been explained by two theories. One theory (Pfeiffer 36 ) suggests that the disease is due to an autosomal, dominant gene, which is sex-limited in its expression, producing the defect only in females. The other theory (Lenz 3 ) suggests that incontinentia pigmenti is due to a sex-linked gene carried on the X-chromosome. This gene acts as a dominant in females and is lethal in males. The pros and cons of each theory are discussed. The Franceschetti-Jadassohn type of incontinentia pigmenti is clinically and genetically different from the classic type. A third of "transitional" cases occurs in boys and girls. Its genetic mechanism has not yet been determined.