Polymorphism in the beta subunit and Na+ transport.

Primary dysregulation of the epithelial sodium channel, manifested by continuing Na+ channel activity despite dietary salt excess, would cause inappropriate renal sodium reabsorption, blunted sodium excretion, and low-renin hypertension. There are now well-characterized genetic causes of hypertension in human pedigrees, which are explained by inappropriate and/or constitutive activation of the epithelial Na+ channel. Although Liddle's syndrome has been the most thoroughly investigated, the incidence of such activating mutations in the subunits of the Na+ channel appears to be relatively rare. Of continuing interest is the possibility that polymorphisms in the channel subunits could result in activation of the channel in response to normal regulatory influences. One such example is provided by a provocative report by Su et al. In this issue of the journal (J Am Soc Nephrol 1996;7:2543-2549). Despite several important technical limitations of the findings presented in the article, the suggestion that polymorphisms found in defined human populations would affect the regulation of sodium channel activity in response to environmental variables is worthy of serious consideration, and serves as a further stimulus to defining the functional significance of the various polymorphisms described in the subunits of the amiloride-sensitive sodium channel.