![]() ![]() These inheritance patterns may allow the localization of the disease gene to the X chromosome and are important for genetic counseling. Affected females have a 50% probability of passing the disease allele to both their male and female offspring 9, 10, 11 ( Fig. The male genotype is often lethal, but if it is viable, affected males transmit the trait to all of their female offspring and to none of their male offspring. There are approximately twice as many affected females as males because females carry a larger percentage of all X chromosomes. X-linked dominant disease is rare, but identifiable by pedigree analysis. Carrier females are unaffected, but may show variable signs of the disease 9, 10, 11 ( Fig. Furthermore, both male and female offspring of a carrier female have a 50% possibility of inheriting the affected allele. In X-linked recessive diseases, pedigree analysis will reveal that more males are affected than females, and affected fathers pass the carrier state to 100% of their female offspring and none of their male offspring. Given the linkage to the sex of the patient, pedigree analysis may identify some diseases carried on the X chromosome. Life expectancy is normal.The X chromosome also has a disproportionately large number of genes coding for ocular traits 8 ( Table 1, Fig. The ichthyosis is life-long but hyperkeratosis and scaling may improve with age. RXLI represents a benign form of ichthyosis. during winter, when the ichthyosis is often more severe. For adult patients, systemic retinoids are an option, e. Treatment consists in hydrating and softening the skin with the use of lubricating bath oils and emollients containing humectants and keratolytics (e. Female patients have rarely been reported. XLRI is transmitted as an X-linked recessive trait: it affects males and is inherited through female carriers. ![]() Therefore, RXLI may be detected in utero, when maternal estriol levels are measured for prenatal screening for Down syndrome and other disorders. Maternal urine and serum steroid measurements may show decreased estrogen levels. Differential diagnosisĭifferential diagnosis includes ichthyosis vulgaris, autosomal recessive congenital ichthyosis (ARCI), namely lamellar ichthyosis, syndromic RLXI, or multiple sulfatase deficiency. Histology or ultrastructure of the skin is helpful for the differentiation of ichthyosis vulgaris. It is confirmed by biochemical (serum protein electrophoresis, STS activity test of fibroblasts or leukocytes) and molecular/cytogenetic analyses (polymerase chain reaction (PCR), multiple ligation-dependent probe amplification (MLPA), comparative genomic hybridization/comparative microarray analysis (CMA), fluorescent in situ hybridization (FISH)). Diagnostic methodsĭiagnosis is based on clinical findings and family history (scaling in male relatives, history of delayed birth). There are some much rarer syndromic RXLI cases that are due to contiguous gene deletion affecting neighboring genes of the STS gene. STS deficiency leads to increased amounts of CSO4 that inhibit epidermal serine proteases, which in turn results in decreased desquamation of corneocytes with retention hyperkeratosis. cholesterol sulfate CSO4, sulfated steroid hormones). STS codes for a lipid hydrolase of the stratum corneum that participates in the regulation of permeability barrier homeostasis and desquamation by catalyzing the hydrolysis of steroid sulfates (e.g. X-linked ichthyosis is an epidermal lipid metabolism anomaly due to inactivating mutations or deletions in the steroid sulfatase STS gene (Xp22.3). Large deletions involving adjacent genes may result in more complex phenotypes (contiguous gene deletion syndromes like Kallman´s syndrome, the recessive form of X-linked chondrodysplasia punctata, short stature, intellectual disability, or central nervous systems anomalies). Extracutaneous manifestations like testicular maldescent, attention deficit and hyperactivity disorder (ADHD) and/or corneal opacities are possible. Delayed birth (insufficient cervical dilatation) may be observed. Scaling improves with age and during summer. Skin's folds, palms and soles, are normally spared. These scales later evolve into grayish or blackish adherent scales that are pronounced on the trunk, the extensor and flexor sites of the extremities, and the neck (giving the ''dirty-neck'' appearance). Onset may occur within the first days of life with the development of generalized non-erythematous, polygonal, loosely adherent scales. It is the second most common type of ichthyosis with an estimated prevalence of 1/2,000 to 1/6,000 males. ![]()
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