Hypohidrosis, electrolyte imbalance, lacrimal gland dysfunction, ichthyosis and xerostomia syndrome caused by a novel claudin-10 variant in an adult with hypokalaemic metabolic alkalosis.

We report a man in his mid-30s who presented with persistent hypokalaemia and was initially suspected to have Gitelman syndrome because of hypokalaemic metabolic alkalosis, hypocalciuria and normal blood pressure. However, the absence of hypomagnesaemia was atypical, and a urine osmolality that was low relative to a concurrent serum osmolality of 285 mOsm/kg prompted further evaluation, which confirmed a partial urinary concentrating defect on formal testing. Genetic testing identified a novel homozygous frameshift variant in CLDN10 NM_006984.5(CLDN10):c.113del, p.(Thr38Argfs*46) confirming HELIX (hypohidrosis, electrolyte imbalance, lacrimal gland dysfunction, ichthyosis and xerostomia) syndrome. Following the molecular diagnosis, directed re-evaluation revealed longstanding hypohidrosis, dry eyes, xerosis and severe dental caries, consistent with ectodermal involvement. The patient required only short-term oral potassium supplementation after which serum potassium remained stable without ongoing replacement. This case expands the mutational spectrum of HELIX syndrome and highlights the importance of considering this diagnosis in patients with apparent Gitelman syndrome but preserved serum magnesium levels.