Expanding the clinical spectrum of autosomal-recessive renal tubular dysgenesis: Two siblings with neonatal survival and review of the literature

A loss-of-function AGTR1 variant in a critically-ill infant with renal tubular dysgenesis: case presentation and literature review

BACKGROUND

Renal tubular dysgenesis (RTD) is a severe disorder with poor prognosis significantly impacting the proximal tubules of the kidney while maintaining an anatomically normal gross structure. The genetic origin of RTD, involving variants in the ACE, REN, AGT, and AGTR1 genes, affects various enzymes or receptors within the Renin angiotensin system (RAS). This condition manifests prenatally with oligohydramninos and postnatally with persistent anuria, severe refractory hypotension, and defects in skull ossification.

CASE PRESENTATION

In this report, we describe a case of a female patient who, despite receiving multi vasopressor treatment, experienced persistent hypotension, ultimately resulting in early death at five days of age. While there was a history of parental consanguinity, no reported family history of renal disease existed. Blood samples from the parents and the remaining DNA sample of the patient underwent Whole Genome Sequencing (WGS). The genetic analysis revealed a rare homozygous loss of function variant (NM_000685.5; c.415C > T; p.Arg139*) in the Angiotensin II Receptor Type 1 (AGTR1) gene.

CONCLUSION

This case highlights the consequence of loss-of-function variants in AGTR1 gene leading to RTD, which is characterized by high mortality rate at birth or during the neonatal period. Furthermore, we provide a comprehensive review of previously reported variants in the AGTR1 gene, which is the least encountered genetic cause of RTD, along with their associated clinical features.

RAAS-deficient organoids indicate delayed angiogenesis as a possible cause for autosomal recessive renal tubular dysgenesis

Autosomal Recessive Renal Tubular Dysgenesis (AR-RTD) is a fatal genetic disorder characterized by complete absence or severe depletion of proximal tubules (PT) in patients harboring pathogenic variants in genes involved in the Renin-Angiotensin-Aldosterone System. To uncover the pathomechanism of AR-RTD, differentiation of ACE-/- and AGTR1-/- induced pluripotent stem cells (iPSCs) and AR-RTD patient-derived iPSCs into kidney organoids is leveraged. Comprehensive marker analyses show that both mutant and control organoids generate indistinguishable PT in vitro under normoxic (21% O2) or hypoxic (2% O2) conditions. Fully differentiated (d24) AGTR1-/- and control organoids transplanted under the kidney capsule of immunodeficient mice engraft and mature well, as do renal vesicle stage (d14) control organoids. By contrast, d14 AGTR1-/- organoids fail to engraft due to insufficient pro-angiogenic VEGF-A expression. Notably, growth under hypoxic conditions induces VEGF-A expression and rescues engraftment of AGTR1-/- organoids at d14, as does ectopic expression of VEGF-A. We propose that PT dysgenesis in AR-RTD is primarily a non-autonomous consequence of delayed angiogenesis, starving PT at a critical time in their development.

The contribution of the AT1 receptor to erythropoiesis

The renin-angiotensin system (RAS) comprises a broad set of functional peptides and receptors that play a role in cardiovascular homeostasis and contribute to cardiovascular pathologies. Angiotensin II (Ang II) is the most potent peptide hormone produced by the RAS due to its high abundance and its strong and pleiotropic impact on the cardiovascular system. Formation of Ang II takes place in the bloodstream and additionally in tissues in the so-called local RAS. Of the two Ang II receptors (AT1 and AT2) that Ang II binds to, AT1 is the most expressed throughout the mammalian body. AT1 expression is not restricted to cells of the cardiovascular system but in fact AT1 protein is found in nearly all organs, hence, Ang II takes part in several modulatory physiological processes one of which is erythropoiesis. In this review, we present multiple evidence supporting that Ang II modulates physiological and pathological erythropoiesis processes trough the AT1 receptor. Cumulative evidence indicates that Ang II by three distinct mechanisms influences erythropoiesis: 1) stimulation of renal erythropoietin synthesis; 2) direct action on bone marrow precursor cells; and 3) modulation of sympathetic nerve activity to the bone marrow. The text highlights clinical and preclinical evidence focusing on mechanistic studies using rodent models.