Liddle's syndrome

Liddle's syndrome
Diagram of the inheritance of the syndrome.
Classification and external resources
Specialty	Nephrology
ICD-10	I15.1
OMIM	177200
DiseasesDB	7471

Liddle's syndrome, also called Liddle syndrome and pseudohyperaldosteronism,^[1] is a genetic disorder inherited in an autosomal dominant manner that is characterized by early, and frequently severe, high blood pressure associated with low plasma renin activity, metabolic alkalosis, low blood potassium, and normal to low levels of aldosterone.^[1] Liddle syndrome involves abnormal kidney function, with excess reabsorption of sodium and loss of potassium from the renal tubule, and is treated with a combination of low sodium diet and potassium-sparing diuretic drugs (e.g., amiloride). It is extremely rare, with fewer than 30 pedigrees or isolated cases having been reported worldwide as of 2008.^[2]

Signs and symptoms

Children with Liddle syndrome are frequently asymptomatic. The first indication of the syndrome often is the incidental finding of hypertension during a routine physical exam. Because this syndrome is rare, it may only be considered by the treating physician after the child's hypertension does not respond to medications for lowering blood pressure.

Adults could present with nonspecific symptoms of low blood potassium, which can include weakness, fatigue, palpitations or muscular weakness (shortness of breath, constipation/abdominal distention or exercise intolerance). Additionally, long-standing hypertension could become symptomatic.

Cause

This syndrome is caused by dysregulation of an epithelial sodium channel (ENaC) due to a genetic mutation at the 16p13-p12 locus. These channels are found on the surface of epithelial cells found in the kidneys, lungs, and sweat glands. The ENaC channel transports sodium into cells. The mutation changes a domain in the channel so it is no longer degraded correctly by the ubiquitin proteasome system. Specifically, the PY motif in the protein is deleted or altered so the E3 ligase (Nedd4) no longer recognizes the channel. This lose of ability to be degraded leads to a high amounts of the channel being chronically present in the collecting duct. This results in a hyperaldosteronism like state, since Aldosterone is typically responsible for creating and inserting these channels. The increased sodium resorption leads to increased resorption of water, and hypertension due to an increase in extracellular volume.

Liddle syndrome is inherited in an autosomal dominant fashion.

Diagnosis

Evaluation of a child with persistent high blood pressure usually involves analysis of blood electrolytes and an aldosterone level, as well as other tests. In Liddle's disease, the serum sodium is typically elevated, the serum potassium is reduced,^[3] and the serum bicarbonate is elevated. These findings are also found in hyperaldosteronism, another rare cause of hypertension in children. Primary hyperaldosteronism (also known as Conn's syndrome), is due to an aldosterone-secreting adrenal tumor (adenoma) or adrenal hyperplasia. Aldosterone levels are high in hyperaldosteronism, whereas they are low to normal in Liddle syndrome.

A genetic study of the ENaC sequences can be requested to detect mutations (deletions, insertions, missense mutations) and get a diagnosis.^[4]

Treatment

The treatment is with a low sodium (low salt) diet and a potassium-sparing diuretic that directly blocks the sodium channel. Potassium-sparing diuretics that are effective for this purpose include amiloride and triamterene; spironolactone is not effective because it acts by regulating aldosterone and Liddle syndrome does not respond to this regulation. Amiloride is the only treatment option that is safe in pregnancy. Medical treatment usually corrects both the hypertension and the hypokalemia, and as a result these patients may not require any potassium replacement therapy.

Eponym

It is named after Dr. Grant Liddle (1921–1989), an American endocrinologist at Vanderbilt University, who discovered it in 1963.

See also

• Pseudohyperaldosteronism

References

External links

• Pseudoaldosteronism at NIH's Office of Rare Diseases