X-linked ichthyosis: an update

X-linked ichthyosis is a genetic disorder of keratinization characterized b y a generalized desquamation of large, adherent, dark brown scales. Extracu taneous manifestations include corneal opacity and cryptorchidism. Since 19 78 it has been known that a deficit in steroid sulphatase enzyme (STS) is r esponsible for the abnormal cutaneous scaling, although the exact physiolog ical mechanism remains uncertain. The STS gene has been mapped to the dista l part of the short arm of the X chromosome. Interestingly, this region esc apes S chromosome inactivation and has the highest ratio of chromosomal del etions among all genetic disorders, complete deletions having been found in up to 90% of patients. Diagnosis of patients with X-linked ichthyosis and female carriers is based on biochemical and genetic analysis. The latter cu rrently seems to be the most accurate method in the majority of cases.