Pseudohypoaldosteronism (PHA) is a condition that mimics

hypoaldosteronism Hypoaldosteronism is an endocrinological disorder characterized by decreased levels of the hormone aldosterone. Similarly, isolated hypoaldosteronism is the condition of having lowered aldosterone without corresponding changes in cortisol. (The ...

. However, the condition is due to a failure of ''response'' to

aldosterone Aldosterone is the main mineralocorticoid steroid hormone produced by the zona glomerulosa of the adrenal cortex in the adrenal gland. It is essential for sodium conservation in the kidney, salivary glands, sweat glands, and colon. It plays a c ...

, and levels of aldosterone are actually elevated, due to a lack of feedback inhibition.

Types

Presentation

PHA2 is clinically characterised by hypertension,

hyperkalaemia Hyperkalemia is an elevated level of potassium (K+) in the blood. Normal potassium levels are between 3.5 and 5.0mmol/L (3.5 and 5.0mEq/L) with levels above 5.5mmol/L defined as hyperkalemia. Typically hyperkalemia does not cause symptoms. Occas ...

metabolic acidosis Metabolic acidosis is a serious electrolyte disorder characterized by an imbalance in the body's acid-base balance. Metabolic acidosis has three main root causes: increased acid production, loss of bicarbonate, and a reduced ability of the kidneys ...

and normal renal function.

Mechanism

PHA2 is also known as familial hyperkalaemic hypertension, or Gordon syndrome. The underlying genetic defect leads to increased sodium chloride reabsorption in the distal tubule in the kidney, leading to volume expansion, hypertension and lowered renin levels. The hyperkalemia found in PHA2 is proposed to be a function of diminished sodium delivery to the cortical collecting tubule (potassium excretion is mediated by the renal outer medullary potassium channel ROMK in which sodium reabsorption plays a role). Alternatively, WNK4 mutations that result in a gain of function of the Na-Cl co-transporter may inhibit ROMK activity resulting in hyperkalemia. Unlike in PHA1 in which aldosterone resistance is present, in PHA2 the volume expansion leads to relatively low aldosterone levels.

Treatment

Treatment of severe forms of PHA1 requires relatively large amounts of

sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35. ...

. These conditions also involve

hyperkalemia Hyperkalemia is an elevated level of potassium (K+) in the blood. Normal potassium levels are between 3.5 and 5.0mmol/L (3.5 and 5.0mEq/L) with levels above 5.5mmol/L defined as hyperkalemia. Typically hyperkalemia does not cause symptoms. Occa ...

. In contrast, PHA2 (Gordon's syndrome) requires salt restriction and use of thiazide diuretics to block sodium chloride reabsorption and normalise blood pressure and serum potassium.

History

This syndrome was first described by Cheek and Perry in 1958. Later pediatric endocrinologist Aaron Hanukoglu reported that there are two independent forms of PHA with different inheritance patterns: A renal form with autosomal dominant inheritance exhibiting salt loss mainly from the kidneys, and a multi-system form with autosomal recessive form exhibiting salt loss from kidney, lung, and sweat and salivary glands. The hereditary lack of responsiveness to aldosterone could be due to at least two possibilities: 1. A mutation in the mineralocorticoid receptor that binds aldosterone, or 2. A mutation in a gene that is regulated by aldosterone. Linkage analysis on patients with the severe form of PHA excluded the possibility of linkage of the disease with the mineralocorticoid receptor gene region. Later, the severe form of PHA was discovered to be due to mutations in the genes

SCNN1A The SCNN1A gene encodes for the α subunit of the epithelial sodium channel ENaC in vertebrates. ENaC is assembled as a heterotrimer composed of three homologous subunits α, β, and γ or δ, β, and γ. The other ENAC subunits are encoded by SCN ...

SCNN1B The SCNN1B gene encodes for the β subunit of the epithelial sodium channel ENaC in vertebrates. ENaC is assembled as a heterotrimer composed of three homologous subunits α, β, and γ or δ, β, and γ. The other ENAC subunits are encoded by S ...

, and

SCNN1G The SCNN1G gene encodes for the γ subunit of the epithelial sodium channel ENaC in vertebrates. ENaC is assembled as a heterotrimer composed of three homologous subunits α, β, and γ or δ, β, and γ. The other ENAC subunits are encoded by S ...

that code for the epithelial sodium channel subunits, α, β, and γ, respectively. A stop mutation in the SCNN1A gene has been shown to be associated with female infertility.

References

External links

GeneReviews/NCBI/NIH/UW entry on Pseudohypoaldosteronism Type II
{{Deficiencies of intracellular signaling peptides and proteins Transcription factor deficiencies Nephrology Pediatrics Channelopathies Rare diseases