X - linked ichthyosis (Ichthyosis, X-Linked) - Gen STS.

Ichthyosis encompasses a group of skin diseases which are characterized by cornification (excessive accumulation of large amounts of flakes or dead cells) in the top layer of skin. The recessive X - linked ichthyosis (RXLI) is a genodermatosis included within cornification disorders (MÉDOC) and is characterized by generalized hyperkeratosis and skin peeling. This disease affects males almost exclusively.

Recessive X - linked ichthyosis (RXLI), may occur during the first few days of life with the presence of non - erythematous and generalized polygonal loosely attached scales. These flakes then evolve blackish greyish or attached plates located on the trunk, and flexor extensor surfaces of the limbs and neck. Usually, skin folds, palms of hands and soles of the feet are usually not affected. Desquamation improves with age and during the summer. This disease may be associated with insufficient cervical dilatation during labor. In about 20% of all cases, extracutaneous manifestations may occur as a bad testicular descent, but usually do not lead to hypogonadism. Corneal opacities are common but usually do not affect vision. In addition, approximately 40% of children suffer impaired attention deficit hyperactivity disorder. 25% of patients have an autistic spectrum or related communication difficulties and language.

This disease is due to mutations in the STS gene, located on the short arm of chromosome X (Xp22.32). This gene encodes a lipid stratum corneum hydrolase involved in the regulation of homeostasis of the skin barrier permeability and the desquamation process, catalyzing hydrolysis of steroid sulphates. The encoded protein is located in the endoplasmic reticulum, where it acts as a homodimer.

Mutations identified in the STS gene, inactivated or give rise to deletions, causing a greater amount of CSO4 inhibiting proteases epidermal serine, which in turn results in decreased desquamation of corneocytes and hyperkeratosis by retention. Some cases have been described of recessive X - linked ichthyosis syndromic caused by deletion of the STS gene that affects neighboring genes. In these cases it can be seen Kallman syndrome a hypogonadotropic hypogonadism, ocular albinism type 1, or a hypertrophic pyloric stenosis.

This disease is transmitted with an X - linked recessive pattern and is inherited through female carriers. In males, an altered copy of the gene in each cell is sufficient to cause disease. In women, a mutation must be present in both copies of the gene result in the alteration. Males are affected by X - linked recessive disorders much more frequently than women. A feature of the X - linked inheritance is that fathers can not pass X - linked traits to their sons chromosome.

Tests in IVAMI: in IVAMI perform detection of mutations associated with recessive X - linked ichthyosis, by complete PCR amplification of the exons of the STS gene, and subsequent sequencing.

Samples recommended: EDTA blood collected for separation of blood leukocytes, or impregnated sample card with dried blood (IVAMI may mail the card to deposit the blood sample).