A form of ichthyosis that is often associated with a defective STS gene, inherited as an X-linked recessive, and resulting in the deficiency of the steroid sulfatase enzyme
Ichthyosis is a skin disorder characterized by having a dry, thick, scaly skin. Its name is derived from the Greek ichthys meaning fish. The skin is compared to the scaly outer covering of the fish. The scaly appearance of the skin is due to excessive skin keratinization or cornification. X-linked ichthyosis is one of the many forms of ichthyosis.
X-linked ichthyosis is a form of ichthyosis that is often associated with a defective STS gene. The gene (located on the X chromosome at band Xp22.3) codes for the steroid sulfatase enzyme. The enzyme is essential in the metabolism of steroids. In particular, it catalyzes the breakdown of sulfated steroid precursors to free steroid. X-linked ichthyosis is often due to mutations or deletions in the STS gene. Without a functional STS gene, there is not enough steroid sulfatase produced that will breakdown cholesterol sulfate (a steroid involved in adding cohesion in the outer layers of the skin). Thus, this could lead to the accumulation of the cholesterol sulfate.
X-linked ichthyosis is an X-linked recessive disorder. A heterozygous female would become a carrier of the defective gene and may exhibit mild to no symptoms. A homozygous female carrying two copies of the defective gene would exhibit the trait. Male offspring would also exhibit the trait when he inherits one copy of the gene from a carrier mother.
Inadequate cholesterol sulfate leads to scaling, often brown in colour, on extremities, neck, trunk, and buttocks. Deletions of the STS gene have been associated with other conditions apart from ichthyosis. Corneal opacities and cryptorchidism may also manifest in individuals with X-linked ichthyosis.
- steroid sulfatase deficiency
- X-linked recessive ichthyosis