X_linked ichthyosis = السماك المرتبط بالجنس |
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X-Linked Ichthyosis
X-linked ichthyosis is recessively inherited, with about 90% caused by gene deletion. It is only rarely present at birth. Although female heterozygotes are frequently affected, males have a more severe form of the disorder. The thickness of the adherent scales increases during childhood . In contrast to ichthyosis vulgaris, the flexural creases may be involved.
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Histopathology.
In hyperkeratosis, the granular layer is normal or slightly thickened but not thinned as in dominant ichthyosis vulgaris. The epidermis may be slightly thickened .
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X-linked ichthyosis, like ichthyosis vulgaris, shows a normal rate of epidermal proliferation. The disorder is a retention hyperkeratosis characterized by delayed dissolution of the desmosomal disks in the horny layer.
In contrast to that of ichthyosis vulgaris, the synthesis of keratohyaline granules in X-linked ichthyosis is not defective, and the rate of synthesis is slightly increased (B). The cause of the retention hyperkeratosis in X-linked ichthyosis is the virtual absence of steroid sulfatase activity. This was first recognized in skin fibroblasts but was found subsequently also in the entire epidermis and in leukocytes . X-linked ichthyosis is caused by an extensive deletion of the steroid sulfatase gene . Steroid sulfatase normally acts on cholesteryl sulfate, a product of the Odland bodies that is discharged with them from the granular cells into the intercellular space and provides cell cohesion in the lower stratum corneum. Failure of steroid sulfatase to remove cholesteryl sulfate results in persistent cell cohesion even in the upper stratum corneum and interferes with the normal process of desquamation
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