WNK1 is a serine-threonine kinase, the expression of which is affected in pseudohypoaldosteronism type II, a Mendelian form of arterial hypertension. We characterized human WNK1 transcripts to determine the molecular mechanisms governing WNK1 expression. We report the presence of two promoters generating two WNK1 isoforms with a complete kinase domain. Further variations are achieved by the use of two polyadenylation sites and tissue-specific splicing. We also determined the structure of a kidney-specific isoform regulated by a third promoter and starting at a novel exon. This transcript is kinase defective and has a predominant expression in the kidney compared to the other WNK1 isoforms, with, furthermore, a highly restricted expression profile in the distal convoluted tubule. We confirmed that the ubiquitous and kidneyspecific promoters are functional in several cells lines and identified core promoters and regulatory elements. In particular, a strong enhancer element upstream from the kidney-specific exon seems specific to renal epithelial cells. Thus, control of human WNK1 gene expression of kinase-active or -deficient isoforms is mediated predominantly through the use of multiple transcription initiation sites and tissue-specific regulatory elements.A new family of serine-threonine kinases was recently described. The members of this family lack a lysine at a usually invariant position in the active site and are therefore known as With No Lysine (WNK) protein kinases (17,20). Rat WNK1 was the first member of this family to be characterized; it has a cysteine in place of the conserved lysine residue in subdomain II of the catalytic domain (20). The active lysine is itself located in subdomain I in both rats and humans. In both species, WNK1 is expressed in a wide variety of tissues, and two major transcripts have been identified. One is produced mainly in heart, muscle, and brain, and the other, shorter transcript is produced mainly in kidney (18,20). The substrates of WNK1 are unknown, but WNK1 is capable of autophosphorylation on serine residues, an activity that is increased in vitro by increasing the salt concentration (20). Like many other protein kinases, WNK1 enzymes contain an autoinhibitory domain outside the catalytic domain, which is capable of abolishing kinase activity in vitro (21). There is also evidence that the autophosphorylation sites detected in the activation loop of WNK1 may control kinase activity (21).Mutations in the genes encoding WNK1 and WNK4, two of the other four members of the human WNK family (17), are responsible for pseudohypoaldosteronism type II (PHA2), also known as Gordon syndrome, an autosomal dominant form of human arterial hypertension associated with hyperkalaemia and metabolic acidosis with hyperchloraemia (5). The mutations in the WNK4 gene are missense mutations clustering in highly conserved domains close to those encoding the coiled-coil domains (18). The location and nature of these mutations suggest that they may result in changes in interactions with as-yet-u...

Myxomatous mitral-valve prolapse (MMVP), also called Barlow disease, is a common cardiac abnormality and affects up to 5% of the population. It is characterized by an excess of tissue that leads to billowing of the mitral leaflets, sometimes complicated by prolapse. Typical histological findings include myxomatous degeneration and degradation of collagen and elastin. Previous reports have proposed an autosomal dominant inheritance of the trait, with age- and sex-dependent expression. By systematic echocardiographic screening of the first-degree relatives of 17 patients who underwent mitral-valve repair, we have identified four pedigrees showing such an inheritance. Genomewide linkage analysis of the most informative pedigree (24 individuals, three generations) showed a significant linkage for markers mapping to chromosome 16p, with a two-point maximum LOD score for D16S3068 (Zmax=3.30 at straight theta=0). Linkage to D16S3068 was confirmed in a second family (Zmax=2.02 at straight theta=0) but was excluded for the two remaining families, thus demonstrating the genetic heterogeneity of the disease. Multipoint linkage analysis performed, with nine additional markers, on the two families with linkage gave maximum multipoint LOD scores of 5.45 and 5.68 for D16S3133, according to a conservative and a stringent model, respectively. Haplotype analysis defined a 5-cM minimal MMVP-1 locus between D16S3068 (16p11.2) and D16S420 (16p12. 1) and a 34-cM maximal interval between D16S404 and D16S3068 when recombination events were taken into account only in affected individuals. The identification of this locus represents a first step toward a new molecular classification of mitral-valve prolapse.

Abstract-Mutations of the last exon of the ␤ subunit of the amiloride-sensitive epithelial Na ϩ channel (␤ENaC) can lead to Liddle's syndrome, a rare monogenic form of hypertension. The objective of this study was to test whether more subtle changes of ␤ENaC could be implicated in essential hypertension. After determination of the ␤ENaC coding gene organization (12 exons spanning 23.5 kb), a systematic screening of the last exon of the gene was performed in 525 subjects (475 whites, 50 Afro-Caribbeans), all probands of hypertensive families. This search was extended to the remaining 11 exons in a subset of 101 probands with low-renin hypertension. Seven amino acid changes were detected: G589S, T594M, R597H, R624C, E632G (last exon), G442V, and V434M (exon 8). These genetic variants were more frequent in subjects of African origin (44%) than in whites (1%). The functional properties of the variants were analyzed in Xenopus oocytes by two independent techniques, ie, electrophysiology and 22 Na ϩ uptake. Small but not significant differences were observed between the variants and wild type. The clinical evaluation of the family bearing the G589S variant, which provided the highest relative ENaC activity, did not show a cosegregation between the mutation and hypertension. The present study illustrates the difficulty in establishing a relation of causality between a susceptibility gene and hypertension. Furthermore, it does not favor a substantial role of the ␤ENaC gene in essential hypertension. (Hypertension. 1998;32:129-137.)