GENOTYPE-PHENOTYPE ANALYSIS OF A NEWLY DISCOVERED FAMILY WITH LIDDLES-SYNDROME

Objective To investigate the clinical, biologic, and molecular abnorma lities in a family with Liddle's syndrome and analyze the short-and lo ng-term efficacies of amiloride treatment, Patients The pedigree consi sted of one affected mother and four children, of whom three suffered from early-onset and moderate-to-severe hypertension, Methods In addit ion to the biochemical and hormonal measurements, genetic analysis of the carboxy terminus of the beta subunit of the epithelial sodium chan nel (beta ENaC) was conducted through single-strand conformation analy sis and direct sequencing. The functional properties of the mutation w ere analyzed using the Xenopus expression system and compared with one mutation affecting the proline-rich sequence of the beta ENaC. Result s Mild hypokalemia and suppressed levels of plasma renin and aldostero ne were observed in all affected subjects. Administration of 10 mg/day amiloride for 2 months normalized the blood pressure and plasma potas sium levels of all of the affected subjects, whereas their plasma and urinary aldosterone levels remained surprisingly low. A similar patter n was observed after 11 years of follow-up, but a fivefold increase in plasma aldosterone was observed under treatment with 20 mg/day amilor ide for 2 weeks, Genetic analysis of the beta ENaC revealed a deletion of 32 nucleotides that had modified the open reading frame and introd uced a stop codon at position 582, Expression of this beta 579del32 mu tant caused a 3.7 +/- 0.3-fold increase in the amiloride-sensitive sod ium current, without modification of the unitary properties of the cha nnel, A similar increase was elicited by one mutation affecting the ca rboxy terminus of the beta ENaC. Conclusions This new mutation leading to Liddle's syndrome highlights the importance of the carboxy terminu s of the beta ENaC in the activity of the epithelial sodium channel. S mall doses of amiloride are able to control the brood pressure on a lo ng-term basis in this monogenic form of hypertension.