Mutations and variants of the epithelial sodium channel gene in Liddle's syndrome and primary hypertension

A parent and child with Liddle syndrome diagnosed correctly with the child as the proband: a case report with review of literature

Liddle syndrome (LS) is an autosomal dominant genetic disorder characterized by early onset hypertension, hypokalemia, and low plasma aldosterone or renin concentration. It is caused by mutations in subunits of the epithelial sodium channel (ENaC). The clinical phenotypes of LS are variable and nonspecific, making it prone to both misdiagnosis and missed diagnosis. Genetic analysis is necessary to confirm the diagnosis of LS. Herein, we report the case of a 42-year-old male with LS and a 30-year history of hypertension. He was being treated for possible primary aldosteronism (PA) over the preceding 7 years; however, his hypertension was poorly controlled despite intensive combination therapy. His 13-year-old son served as a proband for a diagnosis of LS, as he had hypertension, hypokalemia, and a significant family history of hypertension. Genetic testing revealed a heterozygous pathological variant in the SCNN1B gene. This led to a diagnosis of LS, as the father was found to harbor the same mutation. Both were treated with ENaC inhibitors and a salt-restricted diet, which improved their symptoms markedly. The son's genetic diagnosis facilitated the subsequent proper diagnosis and treatment of his father. LS causes early onset hypertension; hence, its early diagnosis and treatment can prevent complications. Hereditary hypertension should be considered in cases of early onset hypertension with a significant family history. Patients diagnosed with PA using outdated criteria may have concomitant LS and require careful evaluation of biochemical and endocrine tests according to the current criteria.

A Novel Frame-Shift Mutation in SCNN1B Identified in a Chinese Family Characterized by Early-Onset Hypertension

Background

Liddle syndrome is a form of monogenic hypertension caused by mutations in the three homologous subunits of the epithelial sodium channels (ENaCs), α, β, and γ. It is characterized by early-onset refractory hypertension, hypokalemia, low renin activity, and hypoaldosteronism. In this study, we report a novel frame-shift mutation in SCNN1B responsible for Liddle syndrome in a Chinese family.

Methods

DNA samples were collected from all participants. Whole-exome sequencing was performed in the proband to detect possible causative variants. Sanger sequencing was then conducted in the other family members to verify the candidate variant, and in 100 patients with hypertension and 100 normotensive controls to exclude population genetic polymorphism.

Results

We identified a novel frame-shift mutation (c.1691_1693delinsG) in SCNN1B that was responsible for Liddle syndrome in this family. This mutation leads to the substitution of Arg in place of Gln at codon site 564 and generates a new stop codon at 592, influencing the crucial PY motif and resulting in reduced inactivation of the ENaCs. Aside from the proband, eight family members carried the mutation. Intra-familial phenotypic heterogeneity was observed in the blood pressure and serum potassium levels. Amiloride therapy combined with a low sodium diet is effective to alleviate the symptoms of patients with Liddle syndrome.

Conclusion

c.1691_1693delinsG, a novel frame-shift mutation in the β subunit of ENaC, was identified in a Chinese family with Liddle syndrome by whole-exome sequencing. Phenotypic heterogeneity can make diagnosis of Liddle syndrome difficult on the basis of clinical or biochemical characteristics alone. Genetic analysis is a useful tool allowing timely and accurate diagnosis of Liddle syndrome and playing a guiding role in precise treatment of the disease.

Liddle Syndrome: Review of the Literature and Description of a New Case

Liddle syndrome is an inherited form of low-renin hypertension, transmitted with an autosomal dominant pattern. The molecular basis of Liddle syndrome resides in germline mutations of the SCNN1A, SCNN1B and SCNN1G genes, encoding the α, β, and γ-subunits of the epithelial Na⁺ channel (ENaC), respectively. To date, 31 different causative mutations have been reported in 72 families from four continents. The majority of the substitutions cause an increased expression of the channel at the distal nephron apical membrane, with subsequent enhanced renal sodium reabsorption. The most common clinical presentation of the disease is early onset hypertension, hypokalemia, metabolic alkalosis, suppressed plasma renin activity and low plasma aldosterone. Consequently, treatment of Liddle syndrome is based on the administration of ENaC blockers, amiloride and triamterene. Herein, we discuss the genetic basis, clinical presentation, diagnosis and treatment of Liddle syndrome. Finally, we report a new case in an Italian family, caused by a SCNN1B p.Pro618Leu substitution.

Whole-exome sequencing reveals an inherited R566X mutation of the epithelial sodium channel β-subunit in a case of early-onset phenotype of Liddle syndrome

To comprehensively evaluate a European–American child with severe hypertension, whole-exome sequencing (WES) was performed on the child and parents, which identified causal variation of the proband's early-onset disease. The proband's hypertension was resistant to treatment, requiring a multiple drug regimen including amiloride, spironolactone, and hydrochlorothiazide. We suspected a monogenic form of hypertension because of the persistent hypokalemia with low plasma levels of renin and aldosterone. To address this, we focused on rare functional variants and indels, and performed gene-based tests incorporating linkage scores and allele frequency and filtered on deleterious functional mutations. Drawing upon clinical presentation, 27 genes were selected evidenced to cause monogenic hypertension and matched to the gene-based results. This resulted in the identification of a stop-gain mutation in an epithelial sodium channel (ENaC), SCNN1B, an established Liddle syndrome gene, shared by the child and her father. Interestingly, the father also harbored a missense mutation (p.Trp552Arg) in the α-subunit of the ENaC trimer, SCNN1A, possibly pointing to pseudohypoaldosteronism type I. This case is unique in that we present the early-onset disease and treatment response caused by a canonical stop-gain mutation (p.Arg566*) as well as ENaC digenic hits in the father, emphasizing the utility of WES informing precision medicine.

Development and Diseases of the Collecting Duct System

The collecting duct of the mammalian kidney is important for the regulation of extracellular volume, osmolarity, and pH. There are two major structurally and functionally distinct cell types: principal cells and intercalated cells. The former regulates Na⁺ and water homeostasis, while the latter participates in acid-base homeostasis. In vivo lineage tracing using Cre recombinase or its derivatives such as CreGFP and CreER^T2 is a powerful new technique to identify stem/progenitor cells in their native environment and to decipher the origins of the tissue that they give rise to. Recent studies using this technique in mice have revealed multiple renal progenitor cell populations that differentiate into various nephron segments and collecting duct. In particular, emerging evidence suggests that like principal cells, most of intercalated cells originate from the progenitor cells expressing water channel Aquaporin 2. Mutations or malfunctions of the channels, pumps, and transporters expressed in the collecting duct system cause various human diseases. For example, gain-of-function mutations in ENaC cause Liddle's syndrome, while loss-of-function mutations in ENaC lead to Pseudohypoaldosteronism type 1. Mutations in either AE1 or V-ATPase B1 result in distal renal tubular acidosis. Patients with disrupted AQP2 or AVPR2 develop nephrogenic diabetes insipidus. A better understanding of the function and development of the collecting duct system may facilitate the discovery of new therapeutic strategies for treating kidney disease.

Liddle syndrome: clinical and genetic profiles

Liddle syndrome is a rare autosomal dominant monogenic form of hypertension. The authors analyzed clinical and genetic features of 12 cases of Liddle syndrome, the largest sample size ever reported. Clinical data were studied retrospectively. The exon 13 of the β and γ subunits of the epithelial sodium channel were amplified and sequenced in the peripheral blood leukocytes of the patients. The onset age of the 12 patients was 15.5±3.3 years. Their blood pressures were poorly controlled, and serum potassium levels in most patients were <3.0 mmol/L. Upright plasma renin activity and plasma aldosterone concentration were suppressed in all patients. All patients were treated with triamterene, and blood pressures were well controlled and serum potassium levels returned to normal. The serum creatinine level rose to 124 and 161 μmol/L, respectively, in two patients upon triamterene treatment, and returned to normal soon after treatment was discontinued. Eight mutation alleles were identified, and three mutations were newly identified.

Pseudohypoaldosteronism type 1 and Liddle's syndrome mutations that affect the single-channel properties of the epithelial Na+ channel

These studies test whether three disease-causing mutations in genes (SCNN1A and SCNN1G) encoding subunits of the epithelial Na⁺ channel, ENaC, affect the biophysical and gating properties of this important renal ion channel. The S562P missense mutation in αENaC and the K106_S108delinsN mutation in γENaC are associated with pseudohypoaldosteronism type 1 (PHA1). The N530S missense mutation in γENaC causes Liddle’s syndrome. Incorporation of S562P into αENaC and K106_S108N into γENaC resulted in significant decreases in macroscopic ENaC currents. Conversely, incorporation of N530S into γENaC increased macroscopic ENaC current. The S562P substitution resulted in a nonfunctional channel. The K106_S108N mutation produced a functional channel having a normal macroscopic current–voltage relation, there was a slight but significant decrease in unitary conductance and a marked decrease in single-channel open probability. The N530S substitution increased single-channel open probability having no effect on the macroscopic current–voltage relation or unitary conductance of the channel. These findings are consistent with mutation of residues at 562 in αENaC and 530 in γENaC, and a 3′ splice site in SCNN1G (318-1 G→A; K106_108SdelinsN) resulting in aberrant ENaC activity due to changes in the biophysical and gating properties of the channel. Such changes likely contribute to the cellular mechanism underpinning the PHA1 and Liddle’s syndrome caused by these mutations in ENaC subunits.

Associations of epithelial sodium channel genes with blood pressure: the GenSalt study

In order to investigate associations of SCNN1A, SCNN1G and SCNN1B genes with blood pressure (BP) in Han Chinese population, we included 2 880 participants did not use antihypertensive medication in the month prior to the baseline survey in the current analysis. Forty-four tag-SNPs in epithelial sodium channel (ENaC) genes were selected and genotyped and nine BP measurements were obtained during 3-day examination. In single-marker analyses, we identified significant associations of SCNN1A marker rs13306613 with diastolic BP (DBP) and SCNN1B marker rs12447134 with systolic BP (SBP) under codominant model after Bonferroni correction (P= 2.82×10⁻⁵ and 4.63×10⁻⁴, respectively). In addition, 5 SNPs in SCNN1G and 4 SNPs in SCNN1B achieved nominal significance for SBP, DBP or mean arterial pressure (MAP) under the additive model. For example, the minor C allele of rs5735 in SCNN1G gene was associated with decreased SBP, DBP and MAP (P=0.016, 5.41×10⁻³, and 4.36×10⁻³, respectively). Gene-based results showed significant associations of SCNN1G and SCNN1Bwith BP levels. This study suggested that ENaC genes play important roles in BP regulation in the Han Chinese population. Future studies are warranted to replicate these findings and functional studies are needed to identify true causal variants in ENaC genes.

Molecular genetics of Liddle's syndrome

Liddle's syndrome, an autosomal dominant form of monogenic hypertension, is characterized by salt-sensitive hypertension with early penetrance, hypokalemia, metabolic alkalosis, suppression of plasma rennin activity and aldosterone secretion, and a clear-cut response to epithelial sodium channel (ENaC) blockers but not spironolactone therapy. Our understanding of ENaCs and Na(+) transport defects has expanded greatly over the past two decades and provides detailed insight into the molecular basis of Liddle's syndrome. In this review, we offer an overview of recent advances in understanding the molecular genetics of Liddle's syndrome, involving mutation analysis, molecular mechanisms and genetic testing. The ENaC in the distal nephron is composed of α, β and γ subunits that share similar structures. Mutations associated with Liddle's syndrome are positioned in either β or γ subunits and disturb or truncate a conserved proline-rich sequence (i.e., PY motif), leading to constitutive activation of the ENaC. Genetic testing has made it possible to make accurate diagnoses and develop tailored therapies for mutation carriers.

Phenotype-genotype analysis in two Chinese families with Liddle syndrome

The families with Liddle syndrome show marked phenotypic variation in blood pressure, serum potassium and other clinical manifestations. Here we analyzed the correlation of genotype-phenotype in two Chinese families with Liddle syndrome. The sequence of C-terminus of SCNN1B and SCNN1G were screened in the two families with likely Liddle syndrome. In addition to hypertension and hypokalemia, one of the two pedigrees had sudden death in their family members, so the exons of 428 reported genes-related to cardiovascular diseases were screened as well in the family. A heterozygous βR566X nonsense mutation was found in the proband-1 in the first pedigree, and the proband's sister and father. They showed mild phenotype with hypertension under control. In contrast, two of the four previous studies report that the mutation causes severe phenotype. A heterozygous βR597PfrX607 frameshift mutation was identified in the proband-2 in the second pedigree, showing malignant phenotype including resistant hypertension, hypokalemia, higher PRA and plasma angiotensin II levels. Both the proband-2 and the proband-2's father had sudden death in their twenties, but no meaningful mutations were found by screening of the exons in 428 cardiovascular disease-related genes. However, the same mutation has been related to moderate phenotype in previous studies. Our results confirmed that the phenotypes of Liddle syndrome are varied significantly even with the same mutation. The mechanisms why the same mutation causes very different phenotype need to be explored because intervention of these modifiers may change the disease course and prognosis accordingly.

A family with Liddle syndrome caused by a novel missense mutation in the PY motif of the beta-subunit of the epithelial sodium channel

OBJECTIVE

To identify the gene mutation in β and γ subunits of the epithelial sodium channel (ENaC) in an adolescent and family members with Liddle syndrome, an autosomal dominant form of secondary hypertension.

STUDY DESIGN

We screened an adolescent with severe hypertension who was clinically diagnosed with Liddle syndrome for mutations in the C-terminus of the SCNN1B and SCNN1G genes. We also screened for these mutations in his family members, in 100 hypertensive patients, and in 100 controls.

RESULTS

The index case, a 14-year-old boy, was diagnosed with Liddle syndrome by the identification of a novel missense mutation, P614L, in the PY motif of the β subunit of the ENaC. Testing of relatives considered at risk revealed 6 subjects heterozygous for the mutation. All genetically affected subjects had a history of severe hypertension as well as hypokalemia. No other variants in the β or γ subunits of the ENaC were detected.

CONCLUSION

Based on direct DNA sequencing, we have detected a novel mutation that causes Liddle syndrome. This confirms the diagnosis and helps guide effective therapy for this adolescent and his affected relatives. These findings provide further evidence that the conserved PY motif is critical to regulation of ENaC activity.

Liddle syndrome in a Serbian family and literature review of underlying mutations

Severe and reproducible low-renin hypertension responsive to salt restriction and amiloride-thiazide therapy in a 13-year-old otherwise asymptomatic boy suggested Liddle syndrome. This assumption was strengthened by a positive family history of hypertension poorly responsive to conventional treatment or sudden deaths under 40 years of age in four generations. DNA analysis of the beta and gamma subunits of the epithelial sodium channel revealed a heterozygous mutation c.C1852T (p.Pro618Ser) in the SCNN1B gene in the patient and in both his hypertensive mother and uncle. A PubMed search revealed 21 different disease-causing mutations reported to date, all but two clustering in the cytoplasmic C-terminal regions of either beta (16 mutations) or gamma (5) subunit, leading to a three- to eightfold increase in the amiloride-sensitive sodium current. Inter- and intrafamilial variability in both hypertension and hypokalemia were disclosed, which may not be obligatory among the subjects carrying a Liddle mutation.

CONCLUSION

Liddle syndrome should be considered as a cause of hypertension in children or adolescents particularly with suppressed renin activity. Early diagnosis and appropriately tailored treatment avoid complications of long-term unrecognized or inappropriately managed hypertension.

A clinical phenotype mimicking essential hypertension in a newly discovered family with Liddle's syndrome

BACKGROUND

Liddle's syndrome (LS) is a monogenic form of hypertension simulating a mineralocorticoid excess, and is currently suspected in young hypokalemic hypertensives. The aims of the study were: (i) to evaluate the clinical phenotype of LS in a newly identified Italian family of Sicilian origin carrying a gain-of-function mutation of the β subunit of the epithelial sodium channel (ENaC) (P617L) previously reported by our group in an apparently unrelated Sicilian patient presenting the typical phenotype of LS including hypokalemia; (ii) to determine whether an unknown biological relationship exists between the newly identified family and the family of the proband previously reported.

METHODS

Genetic analysis was performed in the present family, in the individual in which the βP617L mutation was first observed, and in his relatives.

RESULTS

βP617L mutation was identified in the proband and in three maternal relatives. None of them showed hypokalemia. Mild to severe early onset hypertension and left ventricular hypertrophy were present in all of them. Analysis of mitochondrial DNA (mtDNA) and Y chromosome profiles in the present family and in the proband's family previously reported showed the absence of a relationship between them. The availability of only one carrier of the mutation in one of the two families meant that a genetic analysis able to assess a founder effect was not feasible.

CONCLUSIONS

LS should be considered in all cases of early onset hypertension, independently of the plasma potassium concentration. The incidence of LS may be greater than is currently thought, because hypokalemia is not invariably present.

A functional variant of the NEDD4L gene is associated with beneficial treatment response with β-blockers and diuretics in hypertensive patients

OBJECTIVE

The capability of the protein NEDD4L to reduce renal tubular expression of epithelial Na+ channel (ENaC) is influenced by a functional rs4149601 G→A NEDD4L polymorphism. As diuretics and β-blockers inhibit renal sodium reabsorption and renin release, respectively, we hypothesized that the β-blocker or diuretic-induced blood pressure reduction and prevention of cardiovascular disease would be greater in patients with the highest ENaC expression (rs4149601 G-allele), whereas there would be no such genetically mediated differences in treatment efficacy among patients treated with the vasodilator diltiazem.

METHODS

We related rs4149601 status to 6-month blood pressure reduction and risk of cardiovascular events in 5152 hypertensive patients (DBP ≥ 100 mmHg) from the Nordic Diltiazem Study (NORDIL) randomized to either β-blocker and/or diuretic-based treatment or diltiazem-based treatment.

RESULTS

In patients on β-blocker or diuretic monotherapy, carriers of the G-allele had greater SBP reduction (19.5 ± 16.8 vs. 15.0 ± 19.3 mmHg, P < 0.001) and DBP reduction (15.4 ± 8.3vs. 14.1 ± 8.4 mmHg, P = 0.02) and during 4.5 years of follow-up among patients randomized to β-blockers and/or diuretics, carriers of the G-allele had greater protection from cardiovascular events [relative risk (RR) = 0.52, 95% confidence interval (CI) = 0.36-0.74, P < 0.001] as compared to AA homozygotes. Within the diltiazem group, there was no difference in blood pressure reduction or risk of cardiovascular events according to genotype.

CONCLUSION

The functional NEDD4L rs4149601 polymorphism influences the efficacy of β-blocker and/or diuretic-based antihypertensive treatment both in terms of blood pressure reduction and cardiovascular disease protection, whereas diltiazem-based antihypertensive treatment efficacy is not influenced by this NEDD4L polymorphism.

The R563Q mutation of the epithelial sodium channel beta-subunit is associated with hypertension

BACKGROUND

A high prevalence of the R563Q mutation of the epithelial sodium channel β-subunit has been reported in South African hypertensives compared with unrelated normotensive controls. To delineate the effects of this mutation against a more uniform genetic background, this study investigated the association of the mutation with hypertension within affected kindreds.

METHODS

Forty-five index patients and members of their kindreds were studied. Blood pressure, serum potassium and the presence of the R563Q mutation were determined.

RESULTS

Of the 136 individuals studied, 89 were heterozygous for the R563Q mutation and 47 homozygous RR. The mean arterial pressure was significantly higher in the R563Q heterozygous group (p = 0.005) after adjusting for gender, race, age and kindred membership. Of the R563Q heterozygous subjects, 71 (80%) had hypertension, while 17 (36%) of the R563Q homozygous RR subjects were hypertensive. Six R563Q heterozygous subjects had hypokalaemia and one R563Q homozygous RR subject had hypokalaemia, but the difference was not statistically significant. Two heterozygous patients had Liddle's syndrome, both occurring during pregnancy.

CONCLUSION

The R563Q mutation of β-ENaC is associated with hypertension within affected kindreds, but does not usually cause the full Liddle's syndrome phenotype.

Licorice-induced hypertension and common variants of genes regulating renal sodium reabsorption

AIM

To study if gene alterations affecting renal sodium reabsorption associate with susceptibility to licorice-induced hypertension.

METHODS

Finnish subjects (n = 30) with a previously documented incident of licorice-induced hypertension were recruited for the study using a newspaper announcement. Their previous clinical and family histories as well as serum electrolyte levels were examined. DNA samples from all individuals were screened for variants of the genes encoding 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2) and alpha-, beta-, and gamma-subunits of the epithelial sodium channel (ENaC).

RESULTS

Upon licorice predisposition, the patients had a mean blood pressure of 201/118 mmHg. Circulating potassium, renin, and aldosterone levels were low. No significant DNA variations were identified in the 11betaHSD2 gene. Four subjects were heterozygous for beta- and gammaENaC variants previously shown to be associated with hypertension. Furthermore, a novel G insertion (2004-2005insG) in the SCNN1A gene encoding the alphaENaC was identified in two subjects. The frequency of these ENaC variants was significantly higher in subjects with licorice-induced hypertension (6/30 i.e. 20%) than in blood donors (11/301 i.e. 3.7%, P = 0.002).

CONCLUSIONS

Defects of the 11betaHSD2 gene do not constitute a likely cause for licorice-induced hypertension. Variants of the ENaC subunits may render some individuals sensitive to licorice-induced metabolic alterations and hypertension.

A novel epithelial sodium channel gamma-subunit de novo frameshift mutation leads to Liddle syndrome

OBJECTIVE

Liddle syndrome is a rare autosomal-dominant monogenic form of hypertension caused by mutations in the C-termini of the epithelial sodium channel beta- or gamma-subunit encoded by SCNN1B and SCNN1G, respectively, and often presenting with a familial history of hypertension. The purpose of this study was to determine whether mutations of SCNN1B or SCNN1G were present in a patient clinically suspected to have Liddle syndrome with no familial history of hypertension.

DESIGN AND PATIENTS

We screened the C-terminus of SCNN1B and SCNN1G in the patient, and also screened for the mutation in his parents, 50 hypertensive patients and 50 controls.

RESULTS

In this patient, no mutations were found in the C-terminus of SCNN1B. However, we found a frameshift mutation caused by an 'AGCTC' deletion at the 583 codon in SCNN1G. The frameshift resulted in a new termination site at the 585 codon of the gamma-subunit and the deletion of its PY motif. Neither his parents nor 50 randomly selected patients with hypertension nor 50 controls have the mutation, indicating that this is a de novo mutation and not a common genetic polymorphism.

CONCLUSION

The de novo mutation is the first reported frameshift of the gamma-subunit causing Liddle syndrome. These data imply that a familial history of hypertension is not an essential criterion for the diagnosis of Liddle syndrome.

24-h ambulatory blood pressure is linked to chromosome 18q21-22 and genetic variation of NEDD4L associates with cross-sectional and longitudinal blood pressure in Swedes

Numerous linkage studies have indicated chromosome 18q21-22 as a locus of importance for blood pressure regulation. This locus harbors the neural precursor cell expressed developmentally downregulated 4-like (NEDD4L) gene, which is instrumental for the regulation of the amiloride-sensitive epithelial sodium channel (ENaC). In a linkage study of 16 markers (including two single nucleotide polymorphism markers located within the NEDD4L gene) on chromosome 18 between 70-104 cM and ambulatory blood pressure (ABP), in 118 families, the strongest evidence of linkage was found for 24 h and day-time systolic ABP at the NEDD4L locus (82.25 cM) (P=0.0014). In a large population sample (n=4001), we subsequently showed that a NEDD4L gene variant (rs4149601), which by alternative splicing leads to varying expression of a functionally crucial C2 domain, was associated with diastolic blood pressure (DBP) (P=0.03) and DBP progression over time (P=0.04). A genotype combination of the rs4149601 and an intronic NEDD4L marker (rs2288774) was associated with systolic blood pressure (SBP) (P=0.01), DBP (P=0.04), and progression of both SBP (P=0.03) and DBP (P=0.05) over time. A quantitative transmission disequilibrium test in the family material of the rs4149601 supported this NEDD4L variant as being at least partially causative of the linkage result. In conclusion, our findings suggest that the chromosome 18 linkage peak at 82.25 cM is explained by genetic NEDD4L variation affecting cross-sectional and longitudinal blood pressure, possibly as a consequence of altered NEDD4L interaction with ENaC.

Molecular genetics of human hypertension

EH (essential hypertension) is a major public health problem in many countries due to its high prevalence and its association with coronary heart disease, stroke, renal disease, peripheral vascular disease and other disorders. Epidemiological studies have demonstrated that EH is heritable. Owing to the fact that blood pressure is controlled by cardiac output and total peripheral resistance, many molecular pathways are believed to be involved in the disease. In this review, recent genetic studies investigating the molecular basis of EH, including different molecular pathways, will be highlighted.

Genetic variance of SGK-1 is associated with blood pressure, blood pressure change over time and strength of the insulin-diastolic blood pressure relationship

BACKGROUND

Insulin stimulation of the serum- and glucocorticoid-regulated kinase 1 (SGK-1) prolongs the half-life of the epithelial sodium channel, a protein which is essential for blood pressure regulation. The aim of this study was to investigate if variation in the SGK-1 gene is associated with increased blood pressure and strength of the insulin-blood pressure relationship.

METHODS

A promoter C/T, an intron 6 C/T and an exon 8 C/T polymorphism in the SGK-1 gene were genotyped in 4830 subjects from the Malmö Diet and Cancer (MDC) material of whom 4001 were free from antihypertensive medication. Of these, 2171 subjects had also been investigated 11.2 +/- 4.4 years earlier in the Malmö Preventive Project (MPP).

RESULTS

In untreated MDC subjects, intron 6 CC genotype carriers had higher diastolic blood pressure than carriers of the T allele (P = 0.02) and exon 8 C allele carriers had higher systolic blood pressure than TT genotype carriers (P = 0.05). Subjects simultaneously carrying the intron 6 CC genotype and the exon 8 CC or CT genotype (SGK-1 risk) had higher systolic blood pressure (P = 0.03) and higher diastolic blood pressure (P = 0.009) than noncarriers. From MPP to MDC, the percent change in blood pressure per year was higher for systolic blood pressure (P = 0.002) and diastolic blood pressure (P = 0.001) in SGK-1 risk carriers than noncarriers. The correlation between fasting plasma insulin concentration and diastolic blood pressure was stronger in SGK-1 risk carriers than in non-carriers (P = 0.04).

CONCLUSION

Our data suggest that SGK-1 risk carriers are at increased risk of hypertension and are more sensitive to the blood pressure elevating effects associated with hyperinsulinemia.

Genetic determinants of blood pressure regulation

Hypertension is a multifactorial disorder that probably results from the inheritance of a number of susceptibility genes and involves multiple environmental determinants. Existing evidence suggests that the genetic contribution to blood pressure variation is about 30-50%. Although a number of candidate genes have been studied in different ethnic populations, results from genetic analysis are still inconsistent and specific causes of hypertension remain unclear. Furthermore, the abundance of data in the literature makes it difficult to piece together the puzzle of hypertension and to define candidate genes involved in the dynamic of blood pressure regulation. In this review, we attempt to highlight the genetic basis of hypertension pathogenesis, focusing on the most important existing genetic variations of candidate genes and their potential role in the development of this disease. Our objective is to review current knowledge and discuss limitations to clinical applications of genotypic information in the diagnosis, evaluation and treatment of hypertension. Finally, some principles of pharmacogenomics are presented here along with future perspectives of hypertension.

Common variants of the beta and gamma subunits of the epithelial sodium channel and their relation to plasma renin and aldosterone levels in essential hypertension

Background

Rare mutations of the epithelial sodium channel (ENaC) result in the monogenic hypertension form of Liddle's syndrome. We decided to screen for common variants in the ENaC βand γ subunits in patients with essential hypertension and to relate their occurrence to the activity of circulating renin-angiotensin-aldosterone system.

Methods

Initially, DNA samples from 27 patients with low renin/low aldosterone hypertension were examined. The DNA variants were subsequently screened for in 347 patients with treatment-resistant hypertension, 175 male subjects with documented long-lasting normotension and 301 healthy Plasma renin and aldosterone levels were measured under baseline conditions and during postural and captopril challenge tests.

Results

Two commonly occurring βENaC variants (G589S and a novel intronic i12-17CT substitution) and one novel γENaC variant (V546I) were detected. One of these variants occurred in a heterozygous form in 32 patients, a prevalence (9.2%) significantly higher than that in normotensive males (2.9%, p = 0.007) and blood donors (3.0%, p = 0.001). βENaC i12-17CT was significantly more prevalent in the hypertension group than in the two control groups combined (4.6% vs. 1.1%, p = 0.001). When expressed in Xenopus oocytes, neither of the two ENaC amino acid-changing variants showed a significant difference in activity compared with ENaC wild-type. No direct evidence for a mRNA splicing defect could be obtained for the βENaC intronic variant. The ratio of daily urinary potassium excretion to upright and mean (of supine and upright values) plasma renin activity was higher in variant allele carriers than in non-carriers (p = 0.034 and p = 0.048).

Conclusions

At least 9% of Finnish patients with hypertension admitted to a specialized center carry genetic variants of β and γENaC, a three times higher prevalence than in the normotensive individuals or in random healthy controls. Patients with the variant alleles showed an increased urinary potassium excretion rate in relation to their renin levels.

Pharmacogenomics of diuretic drugs: data on rare monogenic disorders and on polymorphisms and requirements for further research

This review summarizes the current status of our knowledge about the role of pharmacogenetic variation in response to diuretics and suggests future research topics for the field. Genes with a role in the pharmacokinetics of most diuretics are renal drug transporters, especially OAT1, OAT3 and OCT2 (genes SLC22A6, SLC22A8 and SLC22A2) whereas variants in carbonic anhydrase (CA), cytochrome P450 enzymes and sulfotransferases are relevant only for specific substances. Genes on the pharmacodynamic side include the primary targets of thiazide, loop, K+-sparing and aldosterone antagonistic diuretics: NCC, NKCC2, ENaC and the mineralocorticoid receptor (genes SLC12A3, SLC12A1, SCNN1A, B, G and NR3C2). Rare variants of these proteins cause Gitelman’s syndrome, Bartter’s syndrome, Liddle’s syndrome or pregnancy-induced hypertension. Polymorphisms in these and in associated proteins such as GNB3, α-adducin and angiotensin-converting enzyme (ACE) seem to be clinically relevant. In conclusion, first knowledge has evolved that efficacy of diuretic drugs may be determined by genetic polymorphisms in genes determining pharmacokinetics and pharmacodynamics of this drug class. In the future, the selection of a diuretic drug or the dosing schedules may be individually chosen based on pharmacogenetic parameters, however, many questions remain to be answered before this fantasy becomes reality.

Pseudohyperaldosteronism: pathogenetic mechanisms

Pseudohyperaldosteronism is characterized by a clinical picture of hyperaldosteronism with suppression of plasma renin activity and aldosterone. Pseudohyperaldosteronism can be due to a direct mineralocorticoid effect, as with desoxycorticosterone, fluorohydrocortisone, fluoroprednisolone, estrogens, and the ingestion of high amounts of glycyrrhetinic acid. A block of 11-hydroxysteroid-dehydrogenase type 2 (11HSD2), the enzyme that converts cortisol into cortisone, at the level of epithelial target tissues of aldosterone, is involved in other cases. This mechanism is related either to a mutation of the gene, which encodes 11HSD2 (apparent mineralocorticoid excess syndrome and some cases of low renin hypertension) or to an acquired reduction of the activity of the enzyme due to glycyrrhetinic acid, carbenoxolone, and grapefruit juice. In other cases saturation of 11HSD2 may be involved as in severe Cushing's syndrome and chronic therapy with some corticosteroids. Recently, an activating mutation of the mineralocorticoid receptor gene has been described. Another genetic cause of pseudohyperaldosteronism is the syndrome of Liddle, which is due to a mutation of the gene encoding for beta and gamma subunits of the sodium channels.

Epithelial sodium channel, salt intake, and hypertension

The epithelial sodium channel (ENaC) is a membrane protein made of three different but homologous subunits (a, b, and g) present in the apical membrane of epithelial cells of, for example, the distal nephron. This channel is responsible for salt reabsorption in the kidney and can cause human diseases by increasing channel function in Liddle's syndrome, a form of hereditary hypertension, or by decreasing channel function in pseudohypoaldosteronism type I, a salt-wasting disease in infancy. This review briefly discusses recent advances in understanding the implication of ENaC in Liddle's syndrome and in pseudohypoaldosteronism type I, both caused by mutations in the SCNN1 (ENaC) genes. Furthermore, it is still an open question to which extent SCNN1 genes coding for ENaC might be implicated in essential hypertension. The development of Scnn1 genetically engineered mouse models will provide the opportunity to test the effect of environmental factors, like salt intake, on the development of this kind of salt- sensitive hypertension.

Liddle's syndrome associated with a point mutation in the extracellular domain of the epithelial sodium channel gamma subunit

OBJECTIVE

To characterize novel type of mutations of the epithelial sodium channel (ENaC) or subunits in patients with Liddle's syndrome, an autosomal dominant form of hypertension.

PATIENTS AND METHODS

DNA samples from two probands with early-onset, treatment-resistant hypertension and suppressed plasma renin activity were initially screened for mutations in the C-terminal exons of the ENaC or subunit genes, using amplification by polymerase chain reaction and direct DNA sequencing.

RESULTS

Two novel mutations causing Liddle's syndrome were identified. One mutation due to a single nucleotide insertion in the exon 13 of ENaC results in a frameshift at codon 601 and abrogates the PY motif similar to all the previously described ENaC mutations causing Liddle's syndrome. The other mutation, substituting serine for asparagine at codon 530 (Asn530Ser) of the extracellular loop of ENaC subunit, was found in a 25-year-old man with hypertension, hypokalemia, low plasma renin activity and low serum aldosterone levels. Hypertension and hypokalemia favorably responded to amiloride or triamterene administration both in the proband and his affected mother. Expression of the mutant Asn530Ser ENaC subunit in oocytes demonstrated a two-fold increase in ENaC activity, compared with the wild-type, without a significant change in cell surface expression of ENaC. This suggests that the gammaENaC Asn530Ser mutation increases the channel open probability, and is consistent with an abnormally high sodium reabsorption in the distal nephron.

CONCLUSIONS

This study describes the first mutation located in the extracellular domain of an ENaC subunit associated with an increased ENaC activity and Liddle's syndrome.

The epithelial Na+ channel: cell surface insertion and retrieval in Na+ homeostasis and hypertension

The epithelial Na+ channel (ENaC) forms the pathway for Na+ absorption in the kidney collecting duct and other epithelia. Dominant gain-of-function mutations cause Liddle's syndrome, an inherited form of hypertension resulting from excessive renal Na+ absorption. Conversely, loss-of-function mutations cause pseudohypoaldosteronism type I, a disorder of salt wasting and hypotension. Thus, ENaC has a critical role in the maintenance of Na+ homeostasis and blood pressure control. Altered Na+ absorption in the lung may also contribute to the pathogenesis of cystic fibrosis. Epithelial Na+ absorption is regulated in large part by mechanisms that control the expression of ENaC at the cell surface. Nedd4, a ubiquitin protein ligase, binds to ENaC and targets the channel for endocytosis and degradation. Liddle's syndrome mutations disrupt the interaction between ENaC and Nedd4, resulting in an increase in the number of ENaC channels at the cell surface. Aldosterone and vasopressin also regulate Na+ absorption to defend against hypotension and hypovolemia. Both hormones increase the expression of ENaC at the cell surface. The goal of this review is to summarize recent data on the regulation of ENaC expression at the cell surface.

Genotypes of the betaENaC gene have little influence on blood pressure level in the Japanese population

The gene for the beta-subunit of the epithelial sodium channel (betaENaC) is one of the most prominent candidate genes being analyzed for an association with human essential hypertension. It is known that a deletion or alteration of PY motif in exon 12 of betaENaC is responsible for Liddle's syndrome. Although the localization of genetic polymorphisms of betaENaC is unique to each population, intensive analysis of individuals of white and African ancestry has demonstrated that genetic variants are localized in exons 8 and 12, with two frequent polymorphisms, G442V in exon 8 and T594M in exon 12. These two mutations are both found in individuals of African ancestry, and might be associated with elevated blood pressure (BP). Previously, we have screened the last two-thirds of exon 12 in the Japanese population, and demonstrated the absence of the T594M mutation and the presence of a novel P592S mutation. In the present study, we further examined the rest of exon 12 and exon 8 in a general population from Ohasama, Japan (the Ohasama Study), using single-strand conformational polymorphism (SSCP) analysis. We screened 803 subjects randomly selected from the representative participants, who measured their home and casual BP. The PCR products presenting a shift in SSCP gels, as well as controls, were directly sequenced by autoanalyzer to identify the mutation. A novel gel shift was noted in exon 12 (n = 8) and sequencing identified a polymorphism at codon Ser 520, leading to no change in amino acid sequence (G77576C TCG-->TCC). In exon 8, all three SSCP variants were heterogynous for V434M (GTG-->ATG), which is coincident with a rare polymorphism in whites. The G442V mutation, however, was absent from the Japanese population. A novel mutation of exon 12 was not associated with a significant difference in clinical features. These results indicate that Japanese people possess three polymorphisms in exon 12, all of which are unique, and one in exon 8. These genetic variants of betaENaC may not influence the BP level of Japanese people.

Genetics of the mineralocorticoid system in primary hypertension

Abnormalities in steroid biosynthesis have been known for years to cause hypertension in some cases of congenital adrenal hyperplasia. In these patients hypertension usually accompanies a characteristic phenotype with abnormal sexual differentiation. Recently, the molecular basis of four forms of severe hypertension transmitted on an autosomal basis but without additional phenotypic features has been elucidated. All these conditions are characterized primarily by low plasma renin, normal or low serum potassium, and salt-sensitive hypertension, indicating an increased mineralocorticoid effect. These four disorders, the glucocorticoid remediable aldosteronism, the syndrome of apparent mineralocorticoid excess, the activating mutation of the mineralocorticoid receptor, and the Liddle syndrome are a consequence of either abnormal biosynthesis, metabolism, or action of steroid hormones, and are ultimately characterized by an overactivation of the epithelial sodium channel in distal renal tubules. Hyperactivity of this channel results in increased sodium reabsorption and volume expansion leading to an increase in blood pressure as well as potassium loss. With the advent of molecular biology in clinical practice, it has become evident that some genetic defect may present with a more discrete phenotype, with only moderate hypertension with or without hypokalemia as the sole feature. A search for genetic disorders of the mineralocorticoid axis should be an integral part of the diagnostic work-up, particularly in young adults with hypertension.

Regulation of epithelial sodium channel activity through a region of the carboxyl terminus of the alpha -subunit. Evidence for intracellular kinase-mediated reactions

The epithelial sodium channel (ENaC) is a heteromultimer composed of three subunits, each having two membrane-spanning domains with intracellular amino and carboxyl termini. Several hormones and proteins regulate channel activity, but the molecular nature of this regulation is unknown. We conducted experiments to determine a possible new site within the carboxyl terminus of the alpha-subunit involved in enhanced channel activity through endogenous kinases. When an alpha-subunit that was truncated to remove a PY motif was expressed in Xenopus oocytes with wild type human beta- and gamma-ENaC subunits, channel activity was greatly enhanced. The removal of the entire intracellular carboxyl terminus of the alpha-subunit eliminated this enhanced basal activity. Using several point mutations, we localized this site to two amino acid residues (Pro(595)-Gly(596)) near the second membrane-spanning domain. The nonspecific kinase inhibitor staurosporine inhibits basal channel activity of wild type ENaC but was ineffective in inhibiting channels mutated at this site. The major effect of these mutations was not on channel kinetics but was largely, if not entirely, on the number of active channels on the cell surface. This region is potentially important in effecting kinase-mediated increases in ENaC activity.

Evaluation of selected polymorphisms of the Mendelian hypertensive disease genes in the Japanese population

It remains to be defined whether molecular variants of the genes underlying Mendelian forms of hypertension play some etiological role in essential hypertension. To pursue this issue, we focused on the following three genes: the epithelial sodium channel (ENaC), 11beta-hydroxysteroid dehydrogenase type 2, and mineralocorticoid receptor genes. Five sequence variations of these genes, which were either previously reported to show significant association with hypertension or identified as "mild" molecular variants, were chosen for our study. Each variation was screened in 247 severe hypertensive patients with early onset (<45 years) and any detectable variations were subsequently characterized in 291 older normotensive subjects (>60 years) for the case-control comparison. We also investigated the significance of association between the tested variants and biochemical parameters reflecting sodium-water homeostasis, such as plasma aldosterone concentration (PAC) and renin activity (PRA). Only the T663A variant (alpha-subunit of ENaC) turned out to be polymorphic in the Japanese population. In disagreement with positive associations previously reported in white and black subjects, we observed no significant association between T663A and hypertension, while allele frequencies of A663 were higher in Japanese (58-64%) compared with a reported prevalence of 29% in whites and 15% in blacks. T663A showed a borderline association (p=0.02) with the PAC/PRA ratio but not with PAC or PRA in the multivariate analysis. Our data did not support the association between Mendelian disease gene variants and essential hypertension in the Japanese. However, the present study did not definitively resolve this issue and further investigation is certainly warranted.

Diagnosis of Liddle syndrome by genetic analysis of beta and gamma subunits of epithelial sodium channel--a report of five affected family members

OBJECTIVE

To screen the gene mutation in beta and gamma subunits of the epithelial sodium channel (ENaC) of a Chinese family, some of whose members are clinically diagnosed as suffering from Liddle syndrome.

METHODS

Twelve family members were recruited to the study. Among them, two brothers had been clinically diagnosed as suffering from Liddle syndrome. Peripheral blood samples were collected from all members of the family and total genomic DNA was prepared for genetic analysis. Polymerase chain reaction (PCR) was used for amplifying the last exon of beta (codon 513-673) and gamma (codon 503-632) subunits of the ENaC gene. PCR products were purified and subjected to a direct DNA sequence analysis.

RESULTS

Genetic analysis of the beta ENaC gene revealed a missense mutation of CCC to CTC at codon 616 in four middle-aged men of the second generation and one young woman of the third generation. There was no mutation of the gamma ENaC gene in any of the individuals examined.

CONCLUSION

Through direct DNA sequencing analysis, we diagnosed the disease present in five members of a Chinese family as Liddle syndrome, and excluded it in some other young offspring suffering from the monogenic disease. Our results provide further evidence that Pro616 is a critical amino acid that has a key role in the inhibition of sodium channel activity.

Epithelial sodium channel pore region. structure and role in gating

Epithelial sodium channels (ENaC) have a crucial role in the regulation of extracellular fluid volume and blood pressure. To study the structure of the pore region of ENaC, the susceptibility of introduced cysteine residues to sulfhydryl-reactive methanethiosulfonate derivatives ((2-aminoethyl)methanethiosulfonate hydrobromide (MTSEA) and [(2-(trimethylammonium)ethyl]methanethiosulfonate bromide (MTSET)) and to Cd(2+) was determined. Selected mutants within the amino-terminal portion (alphaVal(569)-alphaTrp(582)) of the pore region responded to MTSEA, MTSET, or Cd(2+) with stimulation or inhibition of whole cell Na(+) current. The reactive residues were not contiguous but were separated by 2-3 residues where substituted cysteine residues did not respond to the reagents and line one face of an alpha-helix. The activation of alphaS580Cbetagamma mENaC by MTSET was associated with a large increase in channel open probability. Within the carboxyl-terminal portion (alphaSer(583)-alphaSer(592)) of the pore region, only one mutation (alphaS583C) conferred a rapid, nearly complete block by MTSEA, MTSET, and Cd(2+), whereas several other mutant channels were partially blocked by MTSEA or Cd(2+) but not by MTSET. Our data suggest that the outer pore of ENaC is formed by an alpha-helix, followed by an extended region that forms a selectivity filter. Furthermore, our data suggest that the pore region participates in ENaC gating.

Gating induces a conformational change in the outer vestibule of ENaC

The epithelial Na(+) channel (ENaC) is comprised of three homologous subunits (alpha, beta, and gamma). The channel forms the pathway for Na(+) absorption in the kidney, and mutations cause disorders of Na(+) homeostasis. However, little is known about the mechanisms that control the gating of ENaC. We investigated the gating mechanism by introducing bulky side chains at a position adjacent to the extracellular end of the second membrane spanning segment (549, 520, and 529 in alpha, beta, and gammaENaC, respectively). Equivalent "DEG" mutations in related DEG/ENaC channels in Caenorhabditis elegans cause swelling neurodegeneration, presumably by increasing channel activity. We found that the Na(+) current was increased by mutagenesis or chemical modification of this residue and adjacent residues in alpha, beta, and gammaENaC. This resulted from a change in the gating of ENaC; modification of a cysteine at position 520 in betaENaC increased the open state probability from 0. 12 to 0.96. Accessibility to this side chain from the extracellular side was state-dependent; modification occurred only when the channel was in the open conformation. Single-channel conductance decreased when the side chain contained a positive, but not a negative charge. However, alterations in the side chain did not alter the selectivity of ENaC. This is consistent with a location for the DEG residue in the outer vestibule. The results suggest that channel gating involves a conformational change in the outer vestibule of ENaC. Disruption of this mechanism could be important clinically since one of the mutations that increased Na(+) current (gamma(N530K)) was identified in a patient with renal disease.

Japanese individuals do not harbor the T594M mutation but do have the P592S mutation in the C-terminus of the beta-subunit of the epithelial sodium channel: the Ohasama study

OBJECTIVE

To assess the implications of polymorphisms of the amiloride-sensitive epithelial sodium channel in essential hypertension in the Japanese population by determining the incidence of the T594M mutation in the , subunit of the epithelial sodium channel, and by screening the C-terminus of the epithelial sodium channel.

METHODS

Single-strand confirmational polymorphism (SSCP) analysis using two sets of primers which cover the last two-thirds of the last exon coding the B epithelial sodium channel and modification of a specific enzyme restriction site (NlaIII) for the T594M mutation were performed on 803 Japanese subjects. They were randomly selected from the study participants representative of a general population of Ohasama, Japan, who measured their home blood pressure. Polymerase chain reaction (PCR) products presenting a shift in SSCP gel, as well as controls, were directly sequenced by autoanalyser to identify the mutation.

RESULTS

SSCP analysis identified altered migration in five subjects. Four SSCP variants found by sequencing were heterogeneous for the P592S (CCT to TCT) mutation conserving the PY motif, although it was not significantly associated with either home or casual blood pressure values. The resting polymorphism was at codon Thr 594, leading to no change in the amino acid sequence (ACG to ACA). None of the PCR products were modified by NlaIII, indicating the absence of the T594M mutation.

CONCLUSIONS

The epithelial sodium channel variants at the C-terminus are not involved in the common form of essential hypertension in Japanese.

Genetic variation of the gamma subunit of the epithelial Na+ channel and essential hypertension. Relationship with salt sensitivity

We evaluated the association of a common polymorphism in gammaENaC, consisting in a C to G transversion in codon 649, with essential hypertension and to the pressor response to salt in whites. Two hundred fifteen essential hypertensive patients, and 137 normotensive controls were genotyped for the gamma649 ENaC polymorphism by polymerase chain reaction method and diagnostic restriction enzyme digestion. The genotype distribution of the gamma649 ENaC polymorphism in the hypertensives, 129 CC (60%) and 86 CG/GG (40%) was not significantly different from that of the control group, 84 CC (61%) and 53 CG/GG (39%) (P = .81). Salt sensitivity was assessed in a group of 48 patients by 24-h mean blood pressure response to changes in salt intake. Nineteen patients were diagnosed as salt sensitive, whereas 29 had salt-resistant hypertension. The gamma649 ENaC genotype distribution in salt-sensitive patients was 12 CC (63%) and 7 CG/GG (37%), not significantly different from the distribution in the salt-resistant group, 19 CC (65%) and 10 CG/GG (35%), P = .87. The changes in systolic, diastolic, and mean blood pressure as measured by ambulatory blood pressure monitoring, and in plasma renin activity and plasma aldosterone induced by high salt diet were not different among the gamma649 ENaC genotypes. In the present study we found no association between the gamma649 ENaC polymorphism and essential hypertension or salt sensitivity. Although these data do not support a major causative role for this polymorphism, we cannot exclude that a functional mutation elsewhere in ENaC might be associated with essential hypertension.

Ion channels and the control of blood pressure

Ion channels exist in all cells and are enormously varied in structure, function and regulation. Some progress has been made in understanding the role that ion channels play in the control of blood pressure, but the discipline is still in its infancy. Ion channels provide many different targets for intervention in disorders of blood pressure and exciting advances have been made in this field. It is possible that new drugs, as well as antisense nucleotide technology or gene therapy directed towards ion channels, may form a new class of treatments for high and low blood pressure in the future.

Quantitative trait loci for blood pressure exist near the IGF-1, the Liddle syndrome, the angiotensin II-receptor gene and the renin loci in man

Blood pressure (BP) is heritable and finding quantitative trait loci that influence BP is an important step in identifying genes responsible for BP regulation. Sixty-six pairs of dizygotic (DZ) twin subjects and their parents were used in a sib-pair analysis to look for linkage of selected candidate genes to the quantitative trait BP. Microsatellite markers were tested in the vicinity of the gene loci for insulin-like growth factor-1 (IGF-1), Liddle syndrome, autosomal-dominant hypertension with brachydactyly, angiotensinogen, angiotensin II type 1 receptor, angiotensin-converting enzyme, renin, and lipoprotein lipase. BP was measured in a standardized manner. Heart size was determined echocardiographically. Significant linkage was found at the IGF-1, Liddle syndrome, and AT1 receptor gene for systolic BP. Linkage for diastolic BP was found at the autosomal-dominant hypertension with brachydactyly locus. Both systolic and diastolic BP were linked to the renin gene locus. The linkage was most consistent for the IGF-1 gene locus and systolic BP. Linkage was also found between the IGF-1 gene locus and posterior cardiac wall thickness, septal thickness, and left ventricular mass index. It is suggested that these quantitative trait loci may be important for the subsequent detection of allelic variants for elevated BP. Furthermore, these results linking the IGF-1 gene locus to both BP and cardiac dimensions underscore the importance of the IGF-1 gene as a candidate gene for cardiovascular disease.