2.4.1. *KCNJ5*, *CACNA1D*, *ATP1A1*, *ATP2B3*, and *CTNNB1*

Primary aldosteronism is the most common cause of endocrine hypertension [80]. Autonomous secretion of aldosterone from the adrenal glands suppresses endogenous renin production, which results in an increased volume status. The most frequent cause of primary aldosteronism is bilateral adrenal hyperplasia [81], often referred to as idiopathic adrenal hyperplasia. Recent evidence suggests that these lesions harbor areas of hyperplasia due to cytochrome P450 family 11 subfamily B member 2 (CYP11B2)-expressing cells from an unknown germline variants, and at least 1 CYP11B2 positive aldosterone-producing cell cluster (APCC, that typically develops with aging) or microaldosterone-producing adenomas, in part due to calcium or potassium channel variants (Calcium Voltage-Gated Channel Subunit Alpha1 D (*CACNA1D*), 58%; Potassium Voltage-Gated Channel Subfamily J Member 5 (*KCNJ5*), 1%) [82].

Recently, Nanba et al. studied the genetic characteristics of 73 aldosterone-producing adrenocortical adenomas in 79 subjects of African American decent who had primary aldosteronism; 65 subjects had somatic alterations in driver genes. The genetic landscape of these tumors was different than in non-African Americans: alteartions in *CACNA1D* (*n* = 42%), *KCNJ5* (34%), ATPase Na+/K+ Transporting Subunit Alpha 1 (*ATP1A1*) (8%), and ATPase Plasma Membrane Ca2+ Transporting 3 (*ATP2B3*) (4%) represented the spectrum [83]. No variants in *ARMC5* were found in this study. These results suggest that *CACNA1D* could be one of the most frequently mutated aldosterone-driver gene in African Americans, suggesting a possible primary role for calcium channel blockers in the management of these individuals.

Familial or inherited causes of primary aldosteronism are rare and caused by disease-causing germline activating variants in several genes as detailed elsewhere [81].

#### 2.4.2. Bilateral Adrenocortical Hyperplasia

Bilateral adrenocortical hyperplasias are grossly divided into the micronodular and macronodular disease. The micronodular subtypes are usually diagnosed in children and young adults and are either pigmented (primary pigmented nodular adrenocortical disease [PPNAD] as seen in Carney complex) or not pigmented. The macronodular subtypes, which are usually diagnosed in adults over the age of 40, may be sporadic or familial and caused by disease-causing variants in *ARMC5*, Adenomatous Polyposis Coli (*APC*), Multiple Endocrine Neoplasia type 1 (*MEN1*), and Fumarate Hydratase (*FH*) [84–86]. African Americans with hypertension and a biochemical phenotype of hyporeninemic hyperaldosteronism are more likely to have bilateral adrenal hyperplasia, with or without nodules [84,85,87–91].

#### 2.4.3. *ARMC5*

The *ARMC5* gene is a putative tumor-suppressor that is located on chromosome 16p11.2 and belongs to the family of armadillo (ARM)-repeat-containing proteins. In humans, *ARMC5* consists of 8 exons and has an unknown function. The *ARMC5* gene has been recently implicated in endogenous hypercortisolemia due to a rare form of adrenocortical hyperplasia, termed primary bilateral macronodular adrenal hyperplasia (PBMAH) [84,92,93]. This condition is characterized by multiple macronodules (>1 cm) in the adrenal cortex and hypercortisolemia; it is also rarely associated with primary aldosteronism [85]. Biallelic inactivating variants in *ARMC5* (germline and somatic) are required for the development of adrenocortical hyperplasia, which is consistent with the two-hit hypothesis of tumorigenesis [84,85,92]. Most variants in *ARMC5* are frameshift and/or nonsense, and lead to loss of function of the gene. Our group has recently shown that *Armc5* knockout mice died during early embryonic development, while a third of heterozygotes developed hypercorticosteronemia at 18 months of age [94]. Several pathways may be involved in *Armc5* haploinsufficiency, including cyclic AMP (protein kinase A, its catalytic subunit Cα) and the Wnt/β-catenin pathways [94].

Our laboratory has recently identified an association between biallelic variants of *ARMC5* in African Americans and primary aldosteronism [85]. We hypothesized that these variants likely act as a selective advantage for people of African descent to excrete water more slowly as a survival mechanism in hot climates through enhanced excretion of aldosterone from the adrenal cortex [95]. Our initial studies showed that 20 unrelated and two related study subjects (39.3%) harbored 12 germline *ARMC5* variants that were predicted to be damaging by in silico analysis. Interestingly, all patients carrying a variant predicted to be damaging were African Americans (Table 2).


**Table 2.** Genes associated with pulse pressure, systolic, diastolic blood pressure and hypertension. Adapted by permission from Springer Nature: [Springer Nature][Journal of Cardiovascular Translational Research] [Hall, J.L.; Duprez, D.A.; Barac, A.; Rich, S.S. A review of genetics, arterial stiffness, and blood pressure in African



In a different study, we investigated a large cohort of African Americans in the Minority Health Genomics and Translational Research Bio-Repository Database (MH-GRID) study. The MH-GRID genomic database comprises a large group of subjects with hypertension, both resistant and severe subtypes. We hypothesized that a direct association between *ARMC5* variants and increased risk of hypertension in African American exists. 1377 subjects (mean age: 48.25 (SD ± 6.06), controls 43.35 (SD ± 7.23), P = 1.17×10-40) and 44 variants within *ARMC5* (3 common, 4 low frequency and 37 rare variants) were considered for analysis. *ARMC5* variant rs116201073 reached nominal significance (P = 0.044) and odds ratio (OR) = 0.7, suggesting a protective effect for this variant. A set of 16 rare variants significantly associated with hypertension was identified and combined with the common variant, associated with hypertension in the single-variant analysis, representing a variant set associated with hypertension (*P* = 0.0121). These results confirmed our previous report of increased germline *ARMC5* variants that may be associated with hypertension. Further genetic and molecular studies are needed to confirm these findings [103].
