11β-hydroxylase deficiency pathophysiology

Pathogenesis

11β-Hydroxylase deficient congenital adrenal hyperplasia (11β-OH CAH) is an uncommon form of congenital adrenal hyperplasia (CAH) resulting from a defect in the gene encoding the enzyme steroid 11β-hydroxylase which mediates the final step of cortisol synthesis in the adrenal. 11β-OH CAH results in hypertension due to excessive mineralocorticoid effects. It also causes excessive androgen production both before and after birth and can virilize a genetically female fetus or a child of either sex. 11β-OH congenital adrenal hyperplasia resembles 21-hydroxylase deficient CAH in its androgenic manifestations: partial virilization and ambiguous genitalia of genetically female infants, childhood virilization of both sexes, and rarer cases of virilization or infertility of adolescent and adult women. The mineralocorticoid effect differs: hypertension is usually the clinical clue that a patient has 11- rather than 21-hydroxylase CAH. Diagnosis of 11β-OH congenital adrenal hyperplasia is usually confirmed by demonstration of marked elevations of 11-deoxycortisol and 11-deoxycorticosterone (DOC), the substrates of 11β-hydroxylase. Management is similar to that of 21-hydroxylase deficient congenital adrenal hyperplasia except that mineralocorticoids need not be replaced.

Mineralocorticoid effects

Mineralocorticoid manifestations of severe 11β-hydroxylase deficient CAH can be biphasic, changing from deficiency (salt-wasting) in early infancy to excess (hypertension) in childhood and adult life.

Salt-wasting in early infancy does not occur in most cases of 11β-OH CAH but can occur because of impaired production of aldosterone aggravated by inefficiency of salt conservation in early infancy. When it occurs it resembles the salt-wasting of severe 21-hydroxylase deficient CAH: poor weight gain and vomiting in the first weeks of life progress and culminate in life-threatening dehydration, hyponatremia, hyperkalemia, and metabolic acidosis in the first month.

Despite the inefficient production of aldosterone, the more characteristic mineralocorticoid effect of 11β-OH CAH is hypertension. Progressive adrenal hyperplasia due to persistent elevation of ACTH results in extreme overproduction of 11-deoxycorticosterone (DOC) by mid-childhood. DOC is a weak mineralocorticoid, but usually reaches high enough levels in this disease to cause effects of mineralocorticoid excess: salt retention, volume expansion, and hypertension.

Sex steroid effects

Because 11β-hydroxylase activity is not necessary in the production of sex steroids (androgens and estrogens), the hyperplastic adrenal cortex produces excessive amounts of DHEA, androstenedione, and especially testosterone.

These androgens produce effects that are similar to those of 21-hydroxylase deficient CAH. In the severe forms, XX (genetically female) fetuses can be markedly virilized, with ambiguous genitalia that look more male than female, though internal female organs, including ovaries and uterus develop normally.

XY fetuses (genetic males) typically show no abnormal features related to androgen excess. A megalopenis (>22 cm/8.7in) is usually present in male patients.

References

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