Familial Hyperkalemia and Hypertension (FHHt) and KLHL3: Description of a Family with a New Recessive Mutation (S553L) Compared to a Family with a Dominant Mutation, Q309R, with Analysis of Urinary Sodium Chloride Cotransporter.

Background: Familial hyperkalemia and hypertension (FHHt) is an inherited disorder manifested by hyperkalemia and hypertension. The following four causative genes were identified: WNK1, WNK4, CUL3, and KLHL3. For the first 3 genes, inheritance is autosomal dominant. For KLHL3, inheritance is mostly dominant. A few cases with autosomal recessive disease were described. The mechanism of these 2 modes of inheritance is not clear. In the recessive form, the phenotype of heterozygotes is not well described. Methods: Clinical and genetic investigation of members of 2 families was performed, one with recessive FHHt, and the other, an expansion of a family with Q309R KLHL3 dominant mutation, previously reported by us. Urinary exosomal sodium chloride cotransporter (NCC) was measured. Results: A family with recessive FHHt caused by a new KLHL3 mutation, S553L, is described. This consanguineous Jewish family of Yemenite extraction, included 2 homozygous and 7 hetero- zygous affected subjects. Increased urinary NCC was found in the affected members of the family with dominant Q309R KLHL3 mutation. In the recessive S553L family, homozygotes appeared to have increased urinary NCC abundance. Surprisingly, heterozygotes seemed to have also increased urinary NCC, though at an apparently lower degree. This was not accompanied by a clinical phenotype. Conclusions: A new recessive mutation in KLHL3 (S553L) was identified in FHHt. Increased urinary NCC was found in affected members (heterozygous) with dominant KLHL3 Q309R, and in affected members (homozygous) of the recessive form. Unexpectedly, in the recessive disease, heterozygotes seemed to have increased urinary NCC as well, apparently not sufficient quantitatively to produce a clinical phenotype. (C) 2017 S. Karger AG, Basel