Molecular Genetics Monogenic Hypertension Panel

Hypertension is a common condition in adults; however, hypertension in childhood is much less common and more likely due to an underlying genetic disorder. More specifically, monogenic hypertension refers to specific genetic mutations that interfere with renal and adrenal regulation of blood pressure.

Monogenic hypertension should be considered when a child presents with abnormal potassium levels in the presence of suppressed renin secretion and metabolic alkalosis or acidosis. Monogenic hypertension demonstrates three mechanisms of disease each causing a unique set of genetic disorders. The first mechanism involves gain-of-function mutations that cause hyperactivity of renal sodium and chloride reabsorption leading to plasma volume expansion. Examples include Liddle syndrome and Gordon syndrome (pseudohypoaldosteronism). The second mechanism involves deficiencies of enzymes that regulate adrenal steroid hormone synthesis and deactivation. Examples include congenital adrenal hyperplasia due to 11-beta-hydroxylase deficiency. And, the third mechanism involves excess aldosterone synthesis that escapes normal regulatory mechanisms that lead to volumedependent hypertension with suppressed renin. Examples glucocorticoid-remediable aldosteronism.

All forms of monogenic hypertension lead to volume expansion and are associated with low renin, and electrolyte imbalance is highly suggestive of disease. Identifying a genetic form of monogenic hypertension can significantly alter clinical management and reduce morbidity and mortality.

The results from genetic tests can facilitate assessment of levels of risk for patients and lead to more efficient and appropriate medical management. It is recommended that this testing be accompanied by a complete family history and genetic counseling.  
 
Reasons for Referral:

• Molecular confirmation of a clinical diagnosis of monogenic hypertension.
• To aid in decision-making for treatment and management of individuals with monogenic hypertension.
• Testing for individuals with a positive family history for monogenic hypertension (targeted testing is available if familial mutation is known).

Genomic DNA is analyzed using next-generation sequencing (NGS) on the Illumina NextSeq 2000 platform, with target enrichment performed using hybridization-based probes to capture exonic (coding) regions of the gene(s). Single nucleotide variants (SNVs) and small insertions or deletions (INDELs) are identified using the Illumina DRAGEN Enrichment Workflow, executed onboard the NextSeq2000. This pipeline combines software and hardware acceleration to generate high-confidence germline haplotype calls. Clinical and analytical validation of DRAGEN was performed in our laboratory. Based on validation study results, for SNVs, this assay achieves >96% analytical sensitivity and >99% positive predictive value (PPV). For INDELs <50 bp, the analytical sensitivity is >87% and the PPV is >97%. INDELs >50 bp may be detected but the sensitivity for these is reduced.

Exon-level copy number variants (CNVs) are detected using the Germline Copy Number Variation Best Practices pipeline from GATK. A Bayesian model, clinically validated in our laboratory, enables detection of deletions and duplications involving three or more contiguous exons in genes with adequate probe coverage and without complicating factors (e.g. pseudogene homology, short tandem repeats, segmental duplications). Please note that exon-centric microarray remains the gold standard for exonic copy number variant calling. If exon-centric microarray is of interest, please contact the laboratory for additional information.

This test is not designed to detect polynucleotide repeats, low-level mosaicism, structural rearrangements or balanced alterations (e.g. inversions, gene conversion events, translocations, etc.) or variants in difficult regions. Additionally, variants located in regions of insufficient coverage, including introns and promoter regions; pseudogenes; where the reference genome is inaccurate or contains gaps and insertions; and of high GC content may not be detected. This test does not provide complete coverage of all exons and noncoding regions may have limited information and ability to interpret. Variants in introns that are greater than 10 bp from the intron-exon junction may be analyzed. Please contact the laboratory if interrogation of intronic sequence greater than 10 bp from the intron-exon boundary is desired. 

The 16 monogenic hypertension-associated genes are listed below:
CACNA1H, CLCN2, CUL3, CYP11B1, CYP11B2, CYP17A1, HSD11B2, KCNJ5, KLHL3, NR3C1, NR3C2, SCNN1A, SCNN1B, SCNN1G, WNK1, WNK4  

Blood: EDTA or ACD (Solution A or B):

• Adult: 5 mL
• Child: 5 mL
• Infant: 2-3 mL

Saliva: 2 ORAgene™ Saliva Collection Kit(s) (OGR-500) used according to manufacturer instructions. Please contact KDL Client Services for a Saliva Collection Kit for patients that cannot provide a blood sample.

Assisted Saliva: 4 ORAgene™ Saliva Collection Kit(s) (OGR-575) used according to manufacturer instructions. Please contact KDL Client Services for a Saliva Collection Kit for patients that cannot provide a blood sample.

Buccal Cells: 4 CytoSoft™ Cytology Brush (Medical Packaging CYB-1) used according to manufacturer instructions.  Please contact KDL Client Services for a Buccal Collection Kit for patients that cannot provide a blood sample.

Skin Fibroblast: Punch Biopsy (Cell cultures will be prepared at KDL and used for testing), or 2 T-25 confluent flasks

Prenatal:

• Direct Amniotic Fluid (10-20mL)
• Direct CVS
• Direct POC
• Cultured Amniocytes (2 T-25 flasks)
• Cultured CVS (2 T-25 flasks)
• Cultured fetal tissue: Product of Conception (2 T-25 flasks)
• Cord Blood (1-2mL)

DNA: 10µg at a minimum of 60-100ng/µL (DNA must be extracted in a CLIA-certified laboratory or a laboratory meeting equivalent requirements as determined by the CAP and/or CMS).

Notice Regarding Molecular Genetic Testing on Prenatal Specimens:

Maternal cell rule-out testing will be performed on all prenatal specimens received. Please provide maternal blood (or saliva) in addition to the fetal specimen. Additional charges apply for the maternal cell rule-out test.

For routine testing of blood, saliva and buccal swabs, KDL does NOT accept samples from patients within two (2) weeks of a packed cell/platelet transfusion or within four (4) weeks of a whole blood transfusion. For extraordinary circumstances, where testing must be performed within the above windows, please contact our lab.

A REQUISITION FORM MUST ACCOMPANY ALL SAMPLES. Please include detailed clinical information, including ethnicity, clinical history, and family history.

Weekly

6-8 weeks

• Package and ship specimen to remain cold, but not frozen.
• Ship via overnight express, using the FedEx priority overnight label provided.
• Contact Client Services for shipping kits and instructions at (855) 535- 1522.  

1. Raina R, Krishnappa V, Das A, et al. Overview of Monogenic or Mendelian Forms of Hypertension. Front Pediatr. 2019;7:263. Published 2019 Jul 1. doi:10.3389/fped.2019.00263
2. Simonetti GD, Mohaupt MG, Bianchetti MG. Monogenic forms of hypertension. Eur J Pediatr. 2012;171(10):1433-1439. doi:10.1007/s00431-011-1440-7