17,20-lyase deficiency

Isolated 17,20-lyase deficiency (ILD), also called isolated 17,20-desmolase deficiency, is a rare endocrine and autosomal recessive genetic disorder which is characterized by a complete or partial loss of 17,20-lyase activity and, in turn, impaired production of the androgen and estrogen sex steroids. The condition manifests itself as pseudohermaphroditism (partially or fully underdeveloped genitalia) in males, in whom it is considered to be a form of intersex, and, in both sexes, as a reduced or absent puberty/lack of development of secondary sexual characteristics, resulting in a somewhat childlike appearance in adulthood (if left untreated).

Unlike the case of combined 17α-hydroxylase/17,20-lyase deficiency, isolated 17,20-lyase deficiency does not affect glucocorticoid production (or mineralocorticoid levels), and for that reason, does not result in adrenal hyperplasia or hypertension.

Isolated 17,20-lyase deficiency is caused by genetic mutations in the gene CYP17A1, which encodes for 17,20-lyase, while not affecting 17α-hydroxylase, which is encoded by the same gene.

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