Genetic heterogeneity of familial hyperkalaemic hypertension.

BACKGROUND: Familial hyperkalaemic hypertension (FHH) is a Mendelian form of low-renin hypertension characterized by hyperkalaemia and hyperchloraemic acidosis despite a normal glomerular filtration rate. To date, three different loci have been identified, on chromosomes 1, 17 and 12. OBJECTIVE: To test for genetic linkage between the three FHH loci and three new affected kindreds. DESIGN AND METHODS: Clinical, biological and genetic analyses were made of three kindreds, including 11 affected individuals among 25 members. Genotyping was performed using four series of microsatellite markers spanning the chromosomes 1, 17 and 12 loci, and the thiazide-sensitive Na-Cl cotransporter (SLC12A3) gene. RESULTS: Segregation of the trait in each kindred was compatible with an autosomal transmission, the affected individuals displaying reasonably consistent biochemical abnormalities and the expected variability in arterial hypertension. Multipoint linkage analysis excluded linkage with the four candidate loci in kindreds 1 and 2, but not with the chromosome 1 locus in kindred 3. CONCLUSION: These results demonstrate further genetic heterogeneity and that a fourth gene is responsible for FHH in at least two unrelated kindreds. They suggest a variety of molecular defects leading to FHH.

Human hypertension caused by mutations in WNK kinases.

Hypertension is a major public health problem of largely unknown cause. Here, we identify two genes causing pseudohypoaldosteronism type II, a Mendelian trait featuring hypertension, increased renal salt reabsorption, and impaired K+ and H+ excretion. Both genes encode members of the WNK family of serine-threonine kinases. Disease-causing mutations in WNK1 are large intronic deletions that increase WNK1 expression. The mutations in WNK4 are missense, which cluster in a short, highly conserved segment of the encoded protein. Both proteins localize to the distal nephron, a kidney segment involved in salt, K+, and pH homeostasis. WNK1 is cytoplasmic, whereas WNK4 localizes to tight junctions. The WNK kinases and their associated signaling pathway(s) may offer new targets for the development of antihypertensive drugs.

Phenotypic and genetic heterogeneity of familial hyperkalaemic hypertension (Gordon syndrome).

1. Familial hyperkalaemic hypertension (FHH), also called pseudohypoaldosteronism type II (PHA2) or Gordon syndrome, is a rare Mendelian-form of low-renin hypertension. The first cases of FHH were reported approximately 30 years ago and they described the peculiar biochemical abnormalities (i.e. hyperkalaemia and hyperchloraemic acidosis despite a normal glomerular filtration rate). 2. Since then, more than 90 single cases and families have been reported in the literature. These various reports show marked differences in phenotype. 3. Our group has now collected 14 unrelated pedigrees originating from different parts of France and Europe. We confirm the large variations in the age of discovery and in the severity of the biochemical abnormalities from one individual to another and from one family to another one. 4. Blood pressure levels have no significant relationship with hyperkalaemia or hyperchloraemia, but there is a positive relationship with age, as in the normal population. 5. Analyses of clinical features and Mendelian segregation in our families demonstrate autosomal-dominant inheritance, as expected from the literature. 6. Efforts have been made in the past years to unravel the gene responsible for the disease. Until now, a primary responsibility of the gene encoding the thiazide-sensitive Na-Cl cotransporter (SLC12A3) has been excluded in PHA2 families. Three loci have been identified on chromosomes 1 (PHA2A), 17 (PHA2B) and 12 (PHA2C). 7. More recently, analysis of three additional pedigrees, including 10 affected subjects, with over 25 members allowed us to demonstrate further genetic heterogeneity and the existence of at least a fourth locus. 8. The genetic heterogeneity of this syndrome, and thus the variety of molecular defects, suggests the role of either several new components of the same pathway, multiple aldosterone- regulated effectors or direct or indirect partners of the Na-Cl cotransporter.

A new locus on chromosome 12p13.3 for pseudohypoaldosteronism type II, an autosomal dominant form of hypertension.

Pseudohypoaldosteronism type II (PHA2) is a rare autosomal dominant form of volume-dependent low-renin hypertension characterized by hyperkalemia and hyperchloremic acidosis but also by a normal glomerular filtration rate. These features, together with the correction of blood pressure and metabolic abnormalities by small doses of thiazide diuretics, suggest a primary renal tubular defect. Two loci have previously been mapped at low resolution to chromosome 1q31-42 (PHA2A) and 17p11-q21 (PHA2B). We have now analyzed a new, large French pedigree, in which 12 affected members over three generations confirmed the autosomal dominant inheritance. Affected subjects had hypertension together with long-term hyperkalemia (range 5.2-6.2 mmol/liter), hyperchloremia (range: 100-109 mmol/liter), normal plasma creatinine (range: 63-129 mmol/liter) and low renin levels. Genetic linkage was excluded for both PHA2A and PHA2B loci (all LOD scores Z<-3.2 at recombination fraction [theta] 0), as well as for the thiazide-sensitive sodium-chloride cotransporter gene. A genome-wide scan using 383 microsatellite markers showed a strong linkage with the chromosome 12p13 region (maximum LOD score Z=6.18, straight theta=0, at D12S99). Haplotype analysis using 10 additional polymorphic markers led to a minimum 13-cM interval flanked by D12S1652 and D12S336, thus defining a new PHA2C locus. Analysis of two obvious candidate genes (SCNN1A and GNb3) located within the interval showed no deleterious mutation. In conclusion, we hereby demonstrate further genetic heterogeneity of this Mendelian form of hypertension and identify a new PHA2C locus, the most compelling and precise linkage interval described to date.