Monogenic Hypertension Linked to the Renin–Angiotensin–Aldosterone System

Figures

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  Figure 1.. Key Transporters in the aldosterone-sensitive distal nephron by cell type. This figure delineates the primary transporters located in the aldosterone-sensitive distal nephron, organizing them from the proximal to the distal segments. In the early distal convoluted tubule, the Na–Cl cotransporter acts as the principal apical sodium transporter. The basolateral membrane features channels like KCC4 and Kir4.1/5.1 for potassium and others for chloride transport (not shown). The Na–K ATPase facilitates sodium reabsorption by pumping sodium out and importing potassium, creating a conducive gradient. In principal cells within the connecting tubule and cortical collecting duct (CNT/CCD), sodium reabsorption occurs through ENaC on the apical membrane, and potassium is secreted via renal outer medullary K. Kir4.1/5.1 serves as the primary potassium transporter on the basolateral side, with the Na–K ATPase maintaining its critical function. Alpha intercalated cells in the CT/CCD feature an H+ ATPase pump for H+ secretion and an H+/K+ exchanger to balance the secretion of H+ with the absorption of potassium ions.

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  Figure 2.. Dynamics of sodium reabsorption in hypervolemia vs. hyperkalemia. This figure outlines the differences in sodium reabsorption mechanisms between conditions of hypervolemia and hyperkalemia. Normally, WNK4 serves as an inhibitor of the Na–Cl cotransporter (NCC) within the distal nephron. In hypovolemia, marked by high angiotensin II and aldosterone levels, WNK4 suppresses the renal outer medullary potassium channel (ROMK) across the distal nephron but acts as a positive regulator of NCC in the distal convoluted tubules 1 and 2 (DCT1 and DCT2). Additionally, the isoform L-WNK1 is elevated in low potassium conditions, mitigating WNK4’s inhibitory impact on NCC. L-WNK1 phosphorylates and activates NCC through SPAK, prioritizing sodium reabsorption through NCC and maintaining tubular electroneutrality, which reduces sodium availability for the epithelial sodium channel (ENaC) in principal cells and diminishes electronegativity for potassium secretion by ROMK. Conversely, in hyperkalemia, WNK4 inhibits NCC in DCT1, enhancing distal sodium delivery, while serum- and glucocorticoid-inducible kinase 1 (SGK1) activates ENaC and ROMK in the aldosterone-sensitive distal nephron (ASDN),…

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  Figure 3.. Pathways in steroid synthesis and enzyme disorders. This figure illustrates the steroidogenesis pathways and highlights the enzymes affected in congenital adrenal hyperplasia (CAH) types IV, V, and glucocorticoid remediable aldosteronism (GRA). CYP17 (*) represents the 17α-hydroxylase pathway, deficient in CAH type V and CYP11β1 and 2 (**) represent pathway of 11β-hydroxylase, whose deficiency characterizes CAH type IV. Green arrows and CYP11B2/ CYP11B1(***) indicates ACTH inducible CYB11B2 activity resulting from chimeric gene due to unequal crossover of the genes encoding CYP11B1 and CYP11B2. 18-hydroxy cortisol and 18 oxocortisol are products unique to GRA. Key: 3β OH steroid DeHase (3-β hydroxy steroid dehydrogenase), DHEA (dihydroepiandrosterone).

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  Figure 4.. Management of monogenic hypertension patients. This figure outlines the diagnostic approach for patients with monogenic hypertension. Suspicion for Mendelian forms of hypertension arises from clinical observations such as familial history, hypertension presenting at an early age, disturbances in sexual maturity, and imbalances in electrolytes and acid–base levels. Confirmation begins with documenting low renin activity and analyzing serum pH, potassium, and aldosterone levels. Subsequent genetic analysis through targeted next-generation sequencing is advised, focusing on specific genes associated with these conditions. Broad, indiscriminate testing of numerous genes without specific targets is neither practical nor effective.