*3.1. Familial Hyperaldosteronism Type I*

Familial hyperaldosteronism type I (FH type I or GRA, glucocorticoid remediable aldosteronism) is caused by a hybrid *CYP11B1/CYP11B2* gene inherited as an autosomal dominant trait. The hybrid gene results from an asymmetrical crossing over between the highly homologous *CYP11B1* (encoding 11β-hydroxylase) and *CYP11B2* (encoding aldosterone synthase) genes and comprises 5 sequences of *CYP11B1* (including the promoter region) and 3 sequences of *CYP11B2* (including the coding region of aldosterone synthase). Thus, in FH type I, aldosterone synthase is ectopically expressed in the ZF under the control of adrenocorticotropic hormone (ACTH) rather than restricted to the ZG under the control of angiotensin II [13,14].
