[Liddle syndrome].
In 1963 Liddle et al. described a disorder that simulated primary aldosteronism, characterized by severe hypertension and hypokalemia but with negligible secretion of aldosterone. They theoried that this was a disorder in which the renal tubules transport ions with such abnormal facility that the end result simulates that of a mineralcorticoid excess. Later, it was postulated that this disorder could be related to the abnormality of amiloride sensitive Na channel. The activity of amiloride-sensitive Na channels constitutes the rate limiting step for Na reabsorption in Na transporting epithelia. Recently, the primary sequence of the rat amiloride-sensitive epithelial Na+ channel (rENaC) was determined by functional expression cloning and shown to be composed of three homologous subunits: alpha, beta, and gamma. Its expression of all three subunits in Xenopus oocytes markedly increased the magnitude of these currents. Analysis of subjects with Liddle's syndrome demonstrates the mutation of carboxy-terminal domain in alpha, beta, and gamma subunits. The mutations are either premature termination, frameshift mutation, or missense mutations.