X-Linked Ichthyosis

Excerpt

X-linked ichthyosis (MIM #308100), also known as steroid sulfatase (STS) deficiency and X-linked recessive ichthyosis, is a recessive, nonsyndromic genetic skin disorder. This condition is caused by a mutation or deletion in the STS gene, which is responsible for encoding the steroid sulfatase enzyme, causing the complete loss of steroid sulfatase enzyme activity. Although X-linked ichthyosis equally affects all ethnic groups and races worldwide, the condition predominantly affects males rather than females, as suggested by its name. With an incidence of 1 in 2500 to 1 in 6000 males, X-linked ichthyosis is the second most common type of ichthyosis, after ichthyosis vulgaris.

X-linked ichthyosis was first recognized by Dr Wells and Dr Kerr in 1965. Approximately 15% to 20% of individuals with this condition manifest symptoms at birth, which continue to progress, whereas the rest usually develop symptoms over the following weeks. Affected patients can normally produce skin cells but cannot shed them correctly, leading to dry skin that accumulates in the form of polygonal scales. Initially, the symptoms are usually mild and advance to the development of large, polygonal, brownish scales. The extracutaneous features include asymptomatic punctate corneal opacities, cryptorchidism, and cognitive or behavioral disorders, such as attention-deficit hyperactivity disorder (ADHD).

The deficiency of steroid sulfatase results in the accumulation of cholesterol sulfate and depletion of cholesterol levels, leading to an abnormal skin barrier and retention of corneocytes. Although scaling typically does not affect flexural surfaces, such as the popliteal and antecubital fossae, palms, soles, hair, and nails, the anterior surface of the lower extremities is typically the most affected. Unfortunately, a definitive treatment does not exist for X-linked ichthyosis; however, various options are available for long-term management. The primary treatment objectives involve reducing dryness, minimizing scale formation, and enhancing skin appearance without causing irritation.