Familial hyperaldosteronism is a group of inherited conditions in which the adrenal glands, which are small glands located on top of each kidney, produce too much of the hormone aldosterone. Aldosterone helps control the amount of salt retained by the kidneys. Excess aldosterone causes the kidneys to retain more salt than normal, which in turn increases the body's fluid levels and blood pressure. People with familial hyperaldosteronism may develop severe high blood pressure (hypertension), often early in life. Without treatment, hypertension increases the risk of strokes, heart attacks, and kidney failure.

Familial hyperaldosteronism is categorized into three types, distinguished by their clinical features and genetic causes. In familial hyperaldosteronism type I, hypertension generally appears in childhood to early adulthood and can range from mild to severe. This type can be treated with steroid medications called glucocorticoids, so it is also known as glucocorticoid-remediable aldosteronism (GRA). In familial hyperaldosteronism type II, hypertension usually appears in early to middle adulthood and does not improve with glucocorticoid treatment. In most individuals with familial hyperaldosteronism type III, the adrenal glands are enlarged up to six times their normal size. These affected individuals have severe hypertension that starts in childhood. The hypertension is difficult to treat and often results in damage to organs such as the heart and kidneys. Rarely, individuals with type III have milder symptoms with treatable hypertension and no adrenal gland enlargement.

There are other forms of hyperaldosteronism that are not familial. These conditions are caused by various problems in the adrenal glands or kidneys. In some cases, a cause for the increase in aldosterone levels cannot be found.

The various types of familial hyperaldosteronism have different genetic causes. Familial hyperaldosteronism type I is caused by the abnormal joining together (fusion) of two similar genes called CYP11B1 and CYP11B2, which are located close together on chromosome 8. These genes provide instructions for making two enzymes that are found in the adrenal glands.

The CYP11B1 gene provides instructions for making an enzyme called 11-beta-hydroxylase. This enzyme helps produce hormones called cortisol and corticosterone. The CYP11B2 gene provides instructions for making another enzyme called aldosterone synthase, which helps produce aldosterone. When CYP11B1 and CYP11B2 are abnormally fused together, too much aldosterone synthase is produced. This overproduction causes the adrenal glands to make excess aldosterone, which leads to the signs and symptoms of familial hyperaldosteronism type I.

Familial hyperaldosteronism type III is caused by mutations in the KCNJ5 gene. The KCNJ5 gene provides instructions for making a protein that functions as a potassium channel, which means that it transports positively charged atoms (ions) of potassium into and out of cells. In the adrenal glands,the flow of ions through potassium channels produced from the KCNJ5 gene is thought to help regulate the production of aldosterone. Mutations in the KCNJ5 gene likely result in the production of potassium channels that are less selective, allowing other ions (predominantly sodium) to pass as well. The abnormal ion flow results in the activation of biochemical processes (pathways) that lead to increased aldosterone production, causing the hypertension associated with familial hyperaldosteronism type III.

The genetic cause of familial hyperaldosteronism type II is unknown.

Normal Function

The CYP11B1 gene provides instructions for making an enzyme called 11-beta-hydroxylase. This enzyme is found in the adrenal glands, which are located on top of the kidneys. The 11-beta-hydroxylase enzyme is a member of the cytochrome P450 family of enzymes. These enzymes are involved in the formation and breakdown of various molecules within cells.

The 11-beta-hydroxylase enzyme helps produce hormones called cortisol and corticosterone. Specifically, the enzyme helps convert a molecule called 11-deoxycortisol to cortisol, and helps convert another molecule called 11-deoxycorticosterone to corticosterone. These processes are triggered by the release of a hormone called adrenocorticotropic hormone (ACTH) by the pituitary gland, located at the base of the brain.

Cortisol helps maintain blood sugar (glucose) levels, protects the body from physical stress, and suppresses inflammation. Corticosterone is converted to the hormone aldosterone by the aldosterone synthase enzyme, which is produced from the nearby CYP11B2 gene. Aldosterone helps control blood pressure by maintaining proper salt and fluid levels in the body.

Health Conditions Related to Genetic Changes

Congenital adrenal hyperplasia due to 11-beta-hydroxylase deficiency

More than 80 mutations in the CYP11B1 gene have been found to cause congenital adrenal hyperplasia (CAH) due to 11-beta-hydroxylase deficiency, a disorder in which the adrenal glands produce excess male sex hormones (androgens). Most of these mutations change single protein building blocks (amino acids) in the 11-beta-hydroxylase enzyme and decrease the function of the enzyme. CYP11B1 gene mutations that severely reduce or eliminate the function of the enzyme typically result in the classic form of CAH due to 11-beta-hydroxylase deficiency. Mutations that allow for some enzyme function usually result in the non-classic form of the disorder.

Some mutations that cause the classic form of CAH due to 11-beta-hydroxylase deficiency fuse sections of the CYP11B1 gene with sections of a nearby gene called CYP11B2. The added part of the CYP11B2 gene contains a section called a promoter region, which normally controls (regulates) production of the protein made by the CYP11B2 gene. As a result, the CYP11B1 gene is regulated by the CYP11B2 gene promoter region rather than its own promoter region. In addition, the fusion typically deletes parts of the CYP11B1 gene. These changes in the gene's regulation and structure diminish production of 11-beta-hydroxylase.

Both types of CAH due to 11-beta-hydroxylase deficiency interfere with the production of cortisol and corticosterone. The molecules that are used to form these hormones instead build up in the adrenal gland and are converted to androgens. The excess production of androgens leads to abnormalities of sexual development in people with CAH due to 11-beta-hydroxylase deficiency. A buildup of the molecule 11-deoxycorticosterone, the substance that 11-beta-hydroxylase converts to form corticosterone, increases salt retention, leading to high blood pressure (hypertension) in individuals with the classic form of CAH due to 11-beta-hydroxylase deficiency.

Familial hyperaldosteronism

A genetic change affecting the CYP11B1 gene causes familial hyperaldosteronism type I, a disorder that leads to hypertension. This change joins (fuses) a section of the CYP11B1 gene called a promoter region, which normally helps start the production of the 11-beta-hydroxylase enzyme, to the section of the CYP11B2 gene that provides instructions for making aldosterone synthase.

By binding to the CYP11B1 gene's promoter region, ACTH normally triggers production of the 11-beta-hydroxylase enzyme. In the fusion gene, ACTH binding abnormally triggers production of aldosterone synthase. High levels of aldosterone synthase result in excessive aldosterone production, which leads to the hypertension associated with familial hyperaldosteronism type I.

Other Names for This Gene

• C11B1_HUMAN
• CPN1
• CYP11B
• CYPXIB1
• cytochrome P-450c11
• cytochrome P450 11B1, mitochondrial
• cytochrome P450 11B1, mitochondrial isoform 1 precursor
• cytochrome P450 11B1, mitochondrial isoform 2 precursor
• cytochrome p450 XIB1
• cytochrome P450, family 11, subfamily B, polypeptide 1
• cytochrome P450, subfamily XIB (steroid 11-beta-hydroxylase), polypeptide 1
• cytochrome P450C11
• DKFZp686B05283
• FHI
• FLJ36771
• P450C11
• steroid 11-beta-hydroxylase
• steroid 11-beta-monooxygenase

Genomic Location

Normal Function

The CYP11B2 gene provides instructions for making an enzyme called aldosterone synthase (previously known as corticosterone methyloxidase). This enzyme is found in the adrenal glands, which are located on top of the kidneys. Aldosterone synthase is a member of the cytochrome P450 family of enzymes. These enzymes are involved in the formation and breakdown of various molecules within cells.

Aldosterone synthase helps produce a hormone called aldosterone. Aldosterone helps control blood pressure by maintaining proper salt and fluid levels in the body. The aldosterone synthase enzyme is involved in a series of three chemical reactions that produce aldosterone from other (precursor) molecules: the conversion of 11-deoxycorticosterone to corticosterone, the conversion of corticosterone to 18-hydroxycorticosterone, and the conversion of 18-hydroxycorticosterone to aldosterone.

Health Conditions Related to Genetic Changes

Corticosterone methyloxidase deficiency

At least 30 CYP11B2 gene mutations that cause corticosterone methyloxidase deficiency (also known as aldosterone synthase deficiency) have been identified. These mutations lead to insufficient production of aldosterone, which impairs the kidneys' ability to reabsorb salt (sodium chloride or NaCl) into the blood and release potassium in the urine. As a result, excessive amounts of salt in the form of charged atoms (ions) of sodium (Na+) and chlorine (Cl-) leave the body in the urine, while not enough potassium is released. The resulting imbalance of ions in the body underlies the signs and symptoms of this disorder, which include nausea, vomiting, dehydration, low blood pressure, extreme tiredness (fatigue), and muscle weakness.

Familial hyperaldosteronism

A genetic change affecting the CYP11B2 gene causes familial hyperaldosteronism type I, a disorder that leads to high blood pressure (hypertension). This change joins (fuses) the section of the CYP11B2 gene that contains the instructions for making aldosterone synthase to a section of a nearby gene called CYP11B1. The added part of the CYP11B1 gene contains a section called a promoter region, which normally helps start the production of an enzyme called 11-beta-hydroxylase from the CYP11B1 gene.

By binding to the CYP11B1 gene's promoter region, a hormone called adrenocorticotropic hormone (ACTH) normally triggers production of the 11-beta-hydroxylase enzyme. In the fusion gene, ACTH binding abnormally triggers production of aldosterone synthase. High levels of aldosterone synthase result in excessive aldosterone production, which leads to the hypertension associated with familial hyperaldosteronism type I.

Other disorders

Normal variations (polymorphisms) of the CYP11B2 gene have been associated with increased risk of cardiovascular problems including hypertension, stroke caused by a lack of blood flow to the brain (ischemic stroke), and a heart rhythm abnormality called atrial fibrillation in people with heart failure. Researchers suggest that differences in blood pressure control resulting from the CYP11B2 gene variations may lead to increased risk of these cardiovascular problems.

Other Names for This Gene

• ALDOS
• aldosterone synthase
• aldosterone-synthesizing enzyme
• C11B2_HUMAN
• CPN2
• CYP11B
• CYP11BL
• CYPXIB2
• cytochrome P-450Aldo
• cytochrome P-450C18
• cytochrome P450 11B2, mitochondrial
• cytochrome P450 11B2, mitochondrial precursor
• cytochrome P450, family 11, subfamily B, polypeptide 2
• cytochrome P450, subfamily XIB (steroid 11-beta-hydroxylase), polypeptide 2
• mitochondrial cytochrome P450, family 11, subfamily B, polypeptide 2
• P-450C18
• P450aldo
• P450C18
• steroid 11-beta-monooxygenase
• steroid 11-beta/18-hydroxylase
• steroid 18-hydroxylase, aldosterone synthase, P450C18, P450aldo

Genomic Location

The prevalence of familial hyperaldosteronism is unknown. Familial hyperaldosteronism type II appears to be the most common variety. All types of familial hyperaldosteronism combined account for fewer than 1 out of 10 cases of hyperaldosteronism.

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.