X-linked ichthyosis (XLI) differs from ichthyosis vulgaris clinically and biochemically. Which deficiency characterises XLI and explains its pathogenesis?

• A Deficiency of steroid sulfatase causing accumulation of cholesterol sulfate ✓
• B Deficiency of profilaggrin/filaggrin (FLG mutation)
• C Deficiency of transglutaminase-1 (TGM1 gene)
• D Deficiency of lamellar body secretion of lipid

Explanation

X-linked ichthyosis is caused by deficiency of steroid sulfatase (STS gene, Xp22.3), leading to accumulation of cholesterol sulfate in the stratum corneum. Elevated cholesterol sulfate inhibits normal desquamation by inhibiting serine proteases (kallikreins) responsible for corneodesmosome breakdown. Filaggrin deficiency causes ichthyosis vulgaris and atopic predisposition; TGM1 deficiency causes lamellar ichthyosis; lamellar body abnormalities occur in some ARCI forms.

Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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