Genetic screening for monogenic hypertension in hypertensive individuals in a clinical setting

Identification and functional characterization of compound heterozygous CYP11B1 gene mutations

PURPOSE

11β-Hydroxylase deficiency (11β-OHD) is the second leading cause of congenital adrenal hyperplasia (CAH), a rare autosomal recessive disease caused by mutations in the CYP11B1 gene. We previously reported the case of a male Chinese patient with typical 11β-OHD symptoms. Sanger sequencing revealed that the patient carried a splice-site mutation, c.595+1G>A in the CYP11B1 gene. His mother and sister harbored the heterozygous mutation, c.595+1G>A. Paradoxically, Sanger sequencing did not detect any abnormality in the CYP11B1 gene of his father and brother. Therefore, in this study, we aimed to further explore the exact genetic etiology of 11β-OHD in this pedigree and analyze the functional consequence of the c.595+1G>A mutation.

METHODS

Gemomic DNA was extracted from the peripheral blood leukocytes of the family members and normal control individuals, followed by quantitative real-time polymerase chain reaction (qPCR) to detect the copy number of the target CYP11B1 gene fragment. Mutation analysis was also performed via whole-exome sequencing (WES) followed by Sanger sequencing validation. In vitro minigene assay was also performed to investigate the impact of the c.595+1G>A mutation on pre-mRNA splicing.

RESULTS

qPCR results suggested a heterozygous deletion encompassing position c.595+1 along with flanking exonic and intronic sequences in the CYP11B1 gene of the patient and his father. WES followed by Sanger sequencing verified that the patient carried compound heterozygous mutations in the CYP11B1 gene, including a novel 2840-bp deletion (c.395+661_c.1121+180del) and c.595+1G>A, while his father carried the heterozygous c.395+661_c.1121+180del mutation. No other novel CYP11B1 mutations were found in the rest of the family members. Furthermore, minigene assay revealed that the c.595+1G>A mutation resulted in a 70-bp deletion of exon 3 in the mRNA, and this altered the reading frame at amino acid 176 and created a premature stop codon at amino acid 197.

CONCLUSION

We identified a novel 2840-bp-sized large deletion and confirmed that the c.595+1G>A mutation disrupts normal pre-mRNA splicing. Either mutation could significantly alter the reading frame and abolish CYP11B1 enzyme activity. Therefore, our findings widen the mutation spectrum of CYP11B1 and provide an accurate diagnosis of 11β-OHD at a molecular genetic level.

CACNA1D Gene Polymorphisms Associate With Increased Blood Pressure and Salt Sensitivity of Blood Pressure in White Individuals

BACKGROUND

Disease-causing mutations in CACNA1D gene occur in aldosterone-producing adenomas and familial hyperaldosteronism. We determined whether single nucleotide polymorphisms in CACNA1D gene associate with higher aldosterone resulting in salt sensitivity of blood pressure (BP) and increased BP in men and women.

METHODS

Data were obtained from the HyperPATH (International Hypertension Pathotypes) cohort, where participants completed a cross-over intervention of liberal and restricted sodium diets. Multi-Ethnic Genotyping Array identified 104 CACNA1D single nucleotide polymorphisms that met quality control. Single nucleotide polymorphism is rs7612148 strongly associated with systolic BP and was selected for study in 521 White participants in 3 scenarios ([1] hypertensives; [2] normotensives; [3] total population=hypertensives+normotensives) using multivariate regression analysis.

RESULTS

In the total population and hypertensives, but not normotensives, risk allele carriers (CC, GC), as compared with nonrisk allele homozygotes (GG), exhibited higher salt sensitivity of BP and, on liberal sodium diet, higher systolic BP, lower baseline and angiotensin II-stimulated aldosterone, and lower plasma renin activity. On restricted sodium diet, BP was similar across genotypes, suggesting sodium restriction corrected/neutralized the genotype effect on BP. Because increased aldosterone did not seem to drive the increased salt sensitivity of BP and increased BP on liberal sodium diet, we assessed renal plasma flow. Renal plasma flow increase from restricted to liberal sodium diets was blunted in risk allele homozygotes in the total population and in hypertensives. A replication study in another cohort HyperPATH B (International Hypertension Pathotypes Cohort B) confirmed BP-genotype associations.

CONCLUSIONS

CACNA1D rs7612148 risk allele associated with increased BP and salt sensitivity of BP, likely due to an impaired ability to increase renal plasma flow in response to a liberal sodium diet and not to excess aldosterone.

Voltage-gated calcium channels in genetic epilepsies

Voltage-gated calcium channels (VGCC) are abundant in the central nervous system and serve a broad spectrum of functions, either directly in cellular excitability or indirectly to regulate Ca2+ homeostasis. Ca2+ ions act as one of the main connections in excitation-transcription coupling, muscle contraction and excitation-exocytosis coupling, including synaptic transmission. In recent years, many genes encoding VGCCs main α or additional auxiliary subunits have been associated with epilepsy. This review sums up the current state of knowledge on disease mechanisms and provides guidance on disease-specific therapies where applicable.

CACNA1D-Related Channelopathies: From Hypertension to Autism

Tightly controlled Ca²⁺ influx through voltage-gated Ca²⁺ channels (Cavs) is indispensable for proper physiological function. Thus, it is not surprising that Cav loss and/or gain of function have been implicated in human pathology. Deficiency of Cav1.3 L-type Ca²⁺ channels (LTCCs) causes deafness and bradycardia, whereas several genetic variants of CACNA1D, the gene encoding the pore-forming α1 subunit of Cav1.3, have been linked to various disease phenotypes, such as hypertension, congenital hypoglycemia, or autism. These variants include not only common polymorphisms associated with an increased disease risk, but also rare de novo missense variants conferring high risk. This review provides a concise summary of disease-associated CACNA1D variants, whereas the main focus lies on de novo germline variants found in individuals with a neurodevelopmental disorder of variable severity. Electrophysiological recordings revealed activity-enhancing gating changes induced by these de novo variants, and tools to predict their pathogenicity and to study the resulting pathophysiological consequences will be discussed. Despite the low number of affected patients, potential phenotype-genotype correlations and factors that could impact the severity of symptoms will be covered. Since increased channel activity is assumed as the disease-underlying mechanism, pharmacological inhibition could be a treatment option. In the absence of Cav1.3-selective blockers, dihydropyridine LTCC inhibitors clinically approved for the treatment of hypertension may be used for personalized off-label trials. Findings from in vitro studies and treatment attempts in some of the patients seem promising as outlined. Taken together, due to advances in diagnostic sequencing techniques the number of reported CACNA1D variants in human diseases is constantly rising. Evidence from in silico, in vitro, and in vivo disease models can help to predict the pathogenic potential of such variants and to guide diagnosis and treatment in the clinical practice when confronted with patients harboring CACNA1D variants.

The association between Alu hypomethylation and the severity of hypertension

Introduction

Epigenetic changes that cause genomic instability may be the basis of pathogenic processes of age-associated noncommunicable diseases (NCDs). Essential hypertension is one of the most common NCDs. Alu hypomethylation is an epigenetic event that is commonly found in elderly individuals. Epigenomic alterations are also found in age-associated NCDs such as osteoporosis and diabetes mellitus. Alu methylation prevents DNA from being damaged. Therefore, Alu hypomethylated DNA accumulates DNA damage and, as a result, causes organ function deterioration. Here, we report that Alu hypomethylation is a biomarker for essential hypertension.

Results

We investigated Alu methylation levels in white blood cells from normal controls, patients with prehypertension, and patients with hypertension. The hypertension group possessed the lowest Alu methylation level when classified by systolic blood pressure and diastolic blood pressure (P = 0.0002 and P = 0.0088, respectively). In the hypertension group, a higher diastolic blood pressure and a lower Alu methylation level were observed (r = -0.6278). Moreover, we found that changes in Alu hypomethylation in the four years of follow-up in the same person were directly correlated with increased diastolic blood pressure.

Conclusions

Similar to other age-associated NCDs, Alu hypomethylation is found in essential hypertension and is directly correlated with severity, particularly with diastolic blood pressure. Therefore, Alu hypomethylation may be linked with the molecular pathogenesis of high blood pressure and can be used for monitoring the clinical outcome of this disease.

Monogenic forms of low-renin hypertension: clinical and molecular insights

Monogenic disorders of hypertension are a distinct group of diseases causing dysregulation of the renin-angiotensin-aldosterone system and are characterized by low plasma renin activity. These can chiefly be classified as causing (i) excessive aldosterone synthesis (familial hyperaldosteronism), (ii) dysregulated adrenal steroid metabolism and action (apparent mineralocorticoid excess, congenital adrenal hyperplasia, activating mineralocorticoid receptor mutation, primary glucocorticoid resistance), and (iii) hyperactivity of sodium and chloride transporters in the distal tubule (Liddle syndrome and pseudohypoaldosteronism type 2). The final common pathway is plasma volume expansion and catecholamine/sympathetic excess that causes urinary potassium wasting; hypokalemia and early-onset refractory hypertension are characteristic. However, several single gene defects may show phenotypic heterogeneity, presenting with mild hypertension with normal electrolytes. Evaluation is based on careful attention to family history, physical examination, and measurement of blood levels of potassium, renin, and aldosterone. Genetic sequencing is essential for precise diagnosis and individualized therapy. Early recognition and specific management improves prognosis and prevents long-term sequelae of severe hypertension.

Dominant role of CACNA1D exon mutations for blood pressure regulation

BACKGROUND

CACNA1D gene, which encodes the α1 subunit of the Cav1.3 L-type calcium channel effectively regulates intracellular Ca2+ stability. In recent years, clinical studies have shown that the CACNA1D polymorphisms were associated with hypertension.

OBJECTIVE

The purpose of this study was to evaluate the effects of CACNA1D exon mutation on blood pressure (BP) in Sprague-Dawley rats.

METHODS

The rats with CACNA1D p.D307G, CACNA1D p.V936I or CACNA1D p.R1516Q were constructed using CRISPR-Cas9 technology. SBP measurements of rats were taken for 32 weeks. Tissue morphology of rats and vasoactive substances in serum was tested. Furthermore, the effects of L-type calcium channel blocker isradipine and endothelin-1 (ET-1) inhibitor BQ-123 on BP of double mutation rats (CACNA1D p.D307G/p.R1516Q) were tested. Then we examined the effects of CACNA1D gene mutation on gene expression in human umbilical vein endothelial cells (HUVECs) and vascular smooth muscle cells (VSMCs).

RESULTS

Elevated SBP and increased circulating ET-1 was observed in CACNA1D p.D307G mutant rats. Morphological assessments showed that the vascular, cardiac and renal remodeling could also be observed in rats with p.D307G mutant. Cav1.3 protein expression and calcineurin phosphatase activity in VSMCs of rats with CACNA1D p.D307G were increased in vitro, and the vascular ring tension test of mesenteric grade 3 arteries in CACNA1D p.D307G rats were increased in vivo. Furthermore, ET-1 expression were increased in isolated primary aortic endothelial cells in p.D307G mutant rats and transfected p.D307G mutant HUVECs. Finally, double heterozygosity rats with CACNA1D p.D307G/p.R1516Q or CACNA1D p.D307G/p.V936I further accelerated the rise of SBP compared with p.D307G mutation rats, and isradipine and BQ-123 reduced BP to the same extent in CACNA1D p.D307G/p.R1516Q rats.

CONCLUSION

CACNA1D gene is key players in the regulation of blood pressure. CACNA1D mutation rat may be a new hypertension animal model.