Liddle Syndrome with a SCNN1A Mutation: A Case Report and Literature Review.

Introduction: Liddle syndrome is an autosomal dominant monogenic disease that mainly manifests as early-onset hypertension, hypokalaemia and metabolic alkalosis, as well as hyporeninaemia and hypoaldosteronism. The aetiology of Liddle syndrome is missense or frameshift mutations in the SCNN1A, SCNN1B, or SCNN1G genes, which encode for the epithelial sodium channel subunits. Among these, mutations in the SCNN1A gene are very rare.

Case presentation: A Liddle syndrome case caused by a SCNN1A mutation was reported from China. A 59-year-old proband had a 21-year history of chronic hypertension. His blood pressure was poorly controlled with various antihypertensive drugs, and hypokalaemia was found 8 years ago with no definite cause. At this visit, the patient presented with excessive renal potassium excretion and decreased renin activity in the postural stimulation test; however, his aldosterone level was normal. Subsequent genetic testing identified a missense mutation in SCNN1A (c.1475G>A), which encodes for a protein with an altered amino acid at position 492 (p.Arg492Gln). The pedigree investigation found that the older brother and son of the proband also have the same mutation. The patient's serum potassium returned to normal, and blood pressure control was significantly improved after being treated with triamterene.

Conclusion: A middle-aged patient with Liddle syndrome was diagnosed. A new point mutation in the SCNN1A gene was detected in this patient, and the pathogenicity of this mutation was predicted using AlphaFold software, expanding the genetic mutation spectrum of Liddle syndrome. Genetic testing should be improved to exclude monogenic hypertension in patients with hypertension complicated with hypokalaemia.