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Familial hyperaldosteronism type II
Familial hyperaldosteronism type II (FH-II) is a heritable form of primary aldosteronism (PA) characterized by hypertension of varying severity, and non glucocticoid remediable hyperaldosteronism.
ORPHA:404Classification level: Disorder
PA is the most common form of secondary hypertension and is found in 10% of cases. However, familial forms are rare and represent 5% of adult PA cases. FH-II is considered the most common form of familial hyperaldosteronism and it is estimated at around 4% of all PA cases.
Hypertension, of varying severity even within members of the same family, is noted in most patients and occurs during adulthood. FH-II may present either as an aldosterone-producing adenoma (APA; see this term), bilateral adrenal hyperaldosteronism (BAH), or both. Fatigue, and muscle weakness are reported. Complications due to hypertension, chronic increase of aldosterone secretion accompanied with sodium retention and hypokalemia (found in approximately 25% of patients) may occur. In addition, patients with PA are at increased risk of cardiovascular events, such as coronary artery disease, stroke, non-fatal myocardial infarction, atrial fibrillation and heart failure.
The exact etiopathogenetic mechanism is unknown. Linkage analysis has shown an association with the chromosomal region 7p22 but no causal gene has been found to date. Specific heterozygous missense mutations of the KCNJ5 gene (11q24), encoding the G-protein-activated inward rectifier potassium channel GIRK-4 (p.G151E, p.Y152C) and causing FH type III (see this term), have been identified in some rare cases of families with a mild form of FH-III but that resembles FH-II.
FH-II is diagnosed when PA is found in two or more family members by biochemical testing (aldosterone/ plasma renin activity (PRA) ratio testing, fludrocortisone or saline aldosterone suppression testing), and when diagnosis of familial hyperaldosteronism type I (FH-I; see this term) is excluded by hybrid gene testing. Patients show a non-specific variable aldosterone response to upright posture and AngII infusion. Adrenal venous sampling and imaging techniques (computed tomography, magnetic resonance imaging) allow to distinguish lateralized (APA, unilateral adrenal hyperplasia) from bilateral forms of the disease.
FH-II is clinically and biochemically indistinguishable from sporadic PA. Differential diagnosis also includes the other forms of FH (FH-I and FH-III; see these terms).
FH-II is transmitted in an autosomal dominant mode with variable penetrance.
Management and treatment
FH-II does not respond to glucocorticoid treatment. Adrenalectomy is performed in case of APA, and medical therapy with aldosterone antagonists in case of BAH. In case of severe and/or resistant hypertension, additional antihypertensive medication is required.
With treatment prognosis is good. The cardiovascular morbidity of FH-II patients is increased compared to patients with essential hypertension.