Disease of the Month Familial Hyperkalemic Hypertension Juliette Hadchouel,* Ce´line Delaloy,* Se´bastien Faure´,† Jean-Michel Achard,† and Xavier Jeunemaitre* *Colle`ge de France, Paris; INSERM U36, Paris; AP-HP, Department of Genetics, Hoˆpital Europe´en Georges Pompidou; University Paris-Descartes, Faculty of Medicine, Paris, France; and †Division of Nephrology and Department of Physiology, Limoges University Hospital, Limoges, France J Am Soc Nephrol 17: 208–217, 2006. doi: 10.1681/ASN.2005030314 amilial hyperkalemic hypertension (FHHt) syndrome biochemical abnormalities and age or BP, which seemed to (1,2), also known as Gordon syndrome (3) or pseudohy- depend primarily on age in affected individuals (11). This F poaldosteronism type 2 (4), is a rare inherited form of phenotypic variability, associated with sensitivity to thia- low-renin hypertension associated with hyperkalemia and hy- zides—which are widely used in hypertension—and with a low perchloremic metabolic acidosis in patients with a normal GFR probability of this rare disease’s being recognized by most (OMIM no. 145260). This monogenic form of arterial hyperten- doctors may have led to an underestimation of its frequency. sion has excited new interest since the discovery of a new, The mode of inheritance of the disease is consistent with unsuspected molecular pathway that is responsible for both the autosomal dominant transmission in most, if not all, of the biochemical abnormalities and the increase in BP observed. pedigrees reported. However, we have identified two families Genetic analysis has led to the identification of mutations in in which the parents of the affected individuals were first two genes that belong to a new family of kinases, the WNK cousins, suggesting possible autosomal recessive transmission. family. Although the physiologic functions of these kinases and This would provide further evidence of the genetic heteroge- the pathophysiology of FHHt are not completely solved, these neity of the disease. Indeed, three loci have already been im- results have opened up major new avenues toward under- plicated in this disease, and additional loci probably are re- standing the regulation of ion handling in the aldosterone- sponsible for the same apparent phenotype. Genomic analysis sensitive nephron. of kindreds with FHHt revealed no linkage with SLC12A3, encoding the thiazide-sensitive NaCl co-transporter (NCC) (12 Chasing the Gene and our own data). In 1997, Lifton’s group at Yale University Phenotypic and Genetic Heterogeneity demonstrated locus heterogeneity of the trait, with a multilocus Since the first description of the disease by Paver and Pauline logarithm of odds score of 8.1 for linkage to two loci: a 20- to in 1964 (1), approximately 50 other cases and families have been 33-cM interval on chromosome 1q31-q42 (PHA2A locus) and a reported (5,6). The original case was a 15-yr-old boy with severe 21- to 43-cM linkage interval on chromosome 17p11-q21 hypertension (180/120 mmHg) and very high potassium levels (PHA2B locus) (13). Our analysis of a large French pedigree led (7.0 to 8.2 mmol/L). Detailed analyses using different diets and to the identification of a new locus on chromosome 12p13.3 pharmacologic stimuli showed that the kidney was probably (14). We were able to exclude linkage with the previously involved but that the renal tubule reacted normally to an acid identified loci and with SLC12A3 in three other French kin- load and to carbonic anhydrase inhibitor. Sensitivity to thiazide dreds, demonstrating the involvement of at least one other gene diuretics was reported a few years later in unrelated, affected in the disease (15). Thus, at least four different genes are re- individuals (2,7). Gordon’s group reported their first case in sponsible for FHHt, suggesting that this syndrome is actually a 1970 (8) and helped to demonstrate the existence of a unifying set of related disorders (Table 1). Two of these genes were syndrome (5). High levels of variability, in terms of age at identified recently (16). diagnosis, which may vary from the first few weeks of life (9) until late in adulthood (10), have been reported in sporadic and Identification of the WNK1 and WNK4 Genes familial cases. We observed a similarly high level of variability A fruitful collaboration with Lifton’s group led to the iden- in the first 14 FHHt families studied at our center (6), with the tification of deletions and missense mutations in two genes age at diagnosis of index cases ranging from 7 mo to 39 yr. An encoding members of a novel family of serine/threonine ki- analysis of the affected and unaffected individuals of our larg- nases. These two genes, WNK1 and WNK4, were shown to be est kindred showed no relationship between the severity of responsible for the disease in six families (16). One large genomic deletion (41 kb) was found in an Ameri- Published online ahead of print. Publication date available at www.jasn.org. can family, and a smaller deletion (22 kb) was found in a French family. Both of the deletions that were found in these unrelated Address correspondence to: Dr. Xavier Jeunemaitre, INSERM U36, College de France 11, Place Marcelin Berthelot, 75005 Paris, France. Phone: ϩ33-0-1-44-27- kindreds were located in the same part of the first intron of the 16-55; Fax: ϩ33-0-1-44-27-16-91; E-mail: [email protected] WNK1 gene. No mutation was identified in the coding se- Copyright © 2006 by the American Society of Nephrology ISSN: 1046-6673/1701-0208 J Am Soc Nephrol 17: 208–217, 2006 Familial Hyperkalemic Hypertension 209 Table 1. Genetic heterogeneity of familial hyperkalemic hypertension Type Transmission Locus Location Gene Reference FHHt1 Dominant PHA2C 12p13.3 WNK1 Wilson et al. (16) FHHt2 Dominant PHA2B 17q21 WNK4 Wilson et al. (16) FHHt3 Dominant PHA2A 1q31-42 ? Mansfield et al. (13) FHHt4 Dominant PHA2D ? ? Disse-Nicodeme et al. (15) quence of the gene. WNK1 is located at the telomeric part of the first and second coiled-coil domains (Figure 1). They result chromosome 12 (12p12.3). It contains 28 exons in a 156-kb in the substitution of a charged residue in these negatively and segment. This segment is particularly large as a result, in part, positively charged sequences (16,17). As coiled-coil domains of the large size (60 kb) of intron 1 (NM_018979.1). Several are generally thought to be involved in protein–protein inter- WNK1 isoforms have been identified (see below). An analysis actions, the mutations may affect the interaction of WNK4 with of WNK1 transcript levels in leukocytes from affected and its partners. unaffected members of one of these FHHt families revealed that the intronic deletion was associated with five times higher levels of its expression (16). WNK Kinase Structure The identification of mutations in WNK1 and knowledge of WNK (with no lysine [K] [18]) proteins form a small family of the existence of a putative PHA2 locus on chromosomes 1 and serine/threonine kinases that were identified by Xu et al. (19). 17 led to the identification of WNK4, located on 17q21-q22. This They lack a conserved lysine that usually is found in subdo- gene contains 18 exons in a 16-kb segment (NM_032387). WNK1 main II of the catalytic domain that is critical for ATP binding and WNK4 have similar sequences and intron-exon organiza- to the catalytic site and strictly conserved in all other serine/ tions, but the WNK4 mutations that were found in several FHHt threonine kinases that have been identified to date. In WNK, kindreds differ considerably from the WNK1 mutations identi- this lysine is replaced by a cysteine, and the catalytic lysine is fied. The WNK4 mutations are missense mutations that affect located in subdomain I. This new subfamily of protein kinases short (approximately 10 amino acids) sequences that are highly has been found only in multicellular organisms. Four members conserved in the WNK family, immediately downstream from of the family have been identified in humans: WNK1, WNK2, Figure 1. Structure of the human WNK4 gene and description of the familial hyperkalemic hypertension (FHHt) missense mutations. The human WNK4 gene is 16 kb long and contains 19 exons. The kinase domain is encoded by exons 1 to 6, the autoinhibitory (AI) domain is encoded by exons 6 to 7. Exons 7 and 17 encode the first (CC1) and second (CC2) coiled-coil domains, respectively, and the adjacent small motifs, where the FHHt missense mutations were found. These 10 and 16 amino acid motifs are conserved among the WNK family. 210 Journal of the American Society of Nephrology J Am Soc Nephrol 17: 208–217, 2006 WNK3, and WNK4, located on 12p13.3, 9q22.31, Xp11.22, and ity. They generated a homology-based structural model of 17p11-q21, respectively (16,20,21). WNK4, using the WNK1 coordinates. They identified two res- New insight recently has been provided into the structure idues, at positions 318 and 448, that differed between the two and function of these kinases. The structure of the kinase do- enzymes and that seemed to mediate stable binding between main of WNK1 has been resolved at a resolution of 1.8 A (22). WNK1 and Syt2. This may account for the poor phosphoryla- This structure has confirmed that the lysine residue that is tion of synaptotagmin 2 by WNK4 in their experiments. Wang responsible for kinase activity is located in strand ␤2 rather et al. (25), using GST fusion constructs, confirmed the capacity than in ␤3 as in other protein kinases and the precise confor- of WNK1 constructs to autophosphorylate and to phosphory- mation of the activation loop and has identified residues that late the generic substrate histone.