Congenital renal tubular dysplasia and skull ossification defects similar to teratogenic effects of angiotensin converting enzyme (ACE) inhibitors

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.

Prenatal Diagnosis of Autosomal Recessive Renal Tubular Dysgenesis with Anhydramnios Caused by a Mutation in the AGT Gene

Autosomal recessive renal tubular dysgenesis (ARRTD) is a rare and lethal disorder that causes stillbirth or early neonatal death. Most of the reported cases are diagnosed postnatally by a histopathological hallmark of the absence or paucity of differentiated proximal tubules in kidneys. Prenatal diagnosis of ARRTD is challenging because only a few fetal features (e.g., oligohydramnios/anhydramnios, anuria) are associated with this condition. In this study, we report a fetus with ARRTD, which showed anhydramnios and invisible urinary bladder since the second trimester, followed by growth restriction and reversed end diastolic flow in the middle cerebral artery (MCA-REDF). No morphological anomaly was detected on the fetal kidneys during an ultrasound scan. The baby died of refractory hypotension the day after their birth. Genetic analysis of genes that are involved in the renin-angiotensin-aldosterone system (RAAS), which are the known genetic causes of ARRTD, identified a novel, biparental-origin homozygous c.857-619_1269+243delinsTTGCCTTGC mutation in the AGT gene. The mutation is considered as pathogenic because it is cosegregated with ARRTD and detected in other unrelated ARRTD families. Our findings link the fetal ultrasound manifestations to the ARRTD, highlighting clues that are useful for prenatal diagnosis, which warrants confirmatory genotyping of the RAAS genes including oligohydramnios/anhydramnios, anuria (absent filling of a fetal urinary bladder), MCA-REDF, and a morphologically normal kidney.

Prenatal hypocalvaria after prolonged intrauterine exposure to angiotensin II receptor antagonists

We report a case of prenatal exposure to angiotensin II receptor antagonists (ARA II) from the beginning of pregnancy in a patient with a hypokinetic dilated cardiomyopathy. This case report emphasizes the fetal renal impact of prolonged intrauterine exposure to renin-angiotensin system (RAS) blockers, and highlights that this exposure can cause severe prenatal hypocalvaria. This delayed ossification can be reversible after birth, but the presence of anhydramnios indicates an early and irreversible block of RAS blockers in the fetus that is responsible for fetal kidney development abnormalities. This association carries a high risk of neonatal death. Prolonged exposure to ARA II or other RAS blockers remains prohibited throughout pregnancy.

Renal tubular dysgenesis: antenatal ultrasound scanning and molecular investigations in a Saudi Arabian family

Autosomal recessive renal tubular dysgenesis (RTD) is a rare lethal disease affecting renal development before birth. RTD is manifested by anuria and severe hypotension resulting in oligohydramnios and birth defects known as Potter's syndrome. Homozygous or compound heterozygous mutations in genes encoding components of the renin-angiotensin system (ACE, AGT, AGTR1 and REN) have been reported to cause RTD. A consanguineous family with a history of multiple stillbirths was investigated using prenatal ultrasound and molecular genetic analysis of an affected foetus. Prenatal ultrasound scan suggested RTD, and a novel homozygous frameshift mutation c.299_300delAA (p.Lys100Serfs*4) in the REN gene was identified by whole-exome sequencing, which segregated with parental DNA samples. RTD remains a rare but important cause of prenatal and perinatal death and may present with antenatally hyperechogenic kidneys.

Renal tubular dysgenesis

Renal tubular dysgenesis (RTD) is a severe foetal disorder characterised by the absence or poor development of proximal tubules, early onset and persistent anuria (leading to oligohydramnios and the Potter sequence) and ossification defects of the skull. In most cases, early death occurs from pulmonary hypoplasia, anuria and refractory arterial hypotension. RTD may be acquired during foetal development or inherited as an autosomal recessive disease. Inherited RTD is genetically heterogeneous and linked to mutations in the genes encoding the major components of the renin-angiotensin system (RAS): angiotensinogen, renin, angiotensin-converting enzyme or angiotensin II receptor type 1. Mutations result in either the absence of production or lack of efficacy of angiotensin II. Secondary RTD has been observed in various situations, particularly in the donor twin of severe twin-to-twin transfusion syndrome, in foetuses affected with congenital haemochromatosis or in foetuses exposed to RAS blockers. All cases result in renal hypoperfusion. These examples illustrate the importance of a functional RAS in the maintenance of blood pressure and renal blood flow for humans during foetal life. The diagnosis of RTD in an anuric foetus with normal renal sonography results is important for the management of the foetus or neonate. Depending on the genetic or secondary cause of the disease, such findings can lead to genetic counselling or the prevention of recurrence in subsequent pregnancies.

Spectrum of mutations in the renin-angiotensin system genes in autosomal recessive renal tubular dysgenesis

Autosomal recessive renal tubular dysgenesis (RTD) is a severe disorder of renal tubular development characterized by early onset and persistent fetal anuria leading to oligohydramnios and the Potter sequence, associated with skull ossification defects. Early death occurs in most cases from anuria, pulmonary hypoplasia, and refractory arterial hypotension. The disease is linked to mutations in the genes encoding several components of the renin-angiotensin system (RAS): AGT (angiotensinogen), REN (renin), ACE (angiotensin-converting enzyme), and AGTR1 (angiotensin II receptor type 1). Here, we review the series of 54 distinct mutations identified in 48 unrelated families. Most of them are novel and ACE mutations are the most frequent, observed in two-thirds of families (64.6%). The severity of the clinical course was similar whatever the mutated gene, which underlines the importance of a functional RAS in the maintenance of blood pressure and renal blood flow during the life of a human fetus. Renal hypoperfusion, whether genetic or secondary to a variety of diseases, precludes the normal development/ differentiation of proximal tubules. The identification of the disease on the basis of precise clinical and histological analyses and the characterization of the genetic defects allow genetic counseling and early prenatal diagnosis.

Renin-angiotensin system in kidney development: renal tubular dysgenesis

Autosomal recessive renal tubular dysgenesis (RTD) is a severe disorder of renal tubular development characterized by early onset and persistent fetal anuria leading to oligohydramnios and the Potter sequence. At birth, blood pressure is dramatically low and perinatal death occurs in most cases. Skull ossification defects are frequently associated with RTD. The disease is genetically heterogeneous and linked to mutations in the genes encoding any of the components of the renin-angiotensin system (RAS). An intense stimulation of renin production is noted in the kidneys of patients with mutations in the genes encoding angiotensinogen, angiotensin-converting enzyme, or AT1 receptor, whereas absence or increased renin production is associated with REN defects depending on the type of mutation. The severity of the disease underlines the importance of a functional RAS in the maintenance of blood pressure and renal blood flow during fetal life. The absence or poor development of proximal tubules, as well as renal vascular changes, may be attributable to renal hypoperfusion rather than to a morphogenic property of the RAS. The less severe phenotype in mice devoid of RAS may be linked to differences between mice and humans in the time of nephrogenesis and maturation of the RAS. The identification of the disease on the basis of precise clinical and histological analyses and the characterization of the genetic defects allow genetic counseling and early prenatal diagnosis.

A case surviving for over a year of renal tubular dysgenesis with compound heterozygous angiotensinogen gene mutations

Renal tubular dysgenesis (RTD) is a developmental abnormality of the renal proximal tubules found in patients with Potter syndrome. We report a female newborn with RTD who has survived for more than 18 months. Infusions of fresh frozen plasma (FFP) in the early neonatal period were effective in raising and maintaining her blood pressure. Peritoneal dialysis was required until the appearance of spontaneous urination at 29 days after birth. Histopathological examinations of the kidney revealed dilated renal tubular lumina and foamy columnar epithelial cells in the renal tubules. Endocrinological studies showed a discrepancy between low plasma renin activity (<0.1 ng/ml/hr) and high active renin concentration (135,000 pg/ml), suggesting an aberration in the renin substrate, angiotensinogen. Direct sequencing analysis revealed two novel mutations in the coding region of the angiotensinogen gene (AGT): a nonsense mutation in exon 2 (c.604C > T) and a frameshift deletion at nucleotide 1290 in exon 5 (c.1290delT). The mutations were in the compound heterozygous state, because each parent had each mutation. These findings suggest that angiotensinogen deficiency is one of the causes of RTD. A treatment of the condition with FFP may help to promote long survival.

Renal tubular dysgenesis: report of two cases in a non-consanguineous couple and review of the literature

Renal tubular dysgenesis is a rare congenital abnormality of renal development characterized by short and poorly developed proximal convoluted tubules. It is associated to late-appearing oligohydramnios, Potter's sequence, pulmonary hypoplasia and calvarial bone hypoplasia with enlarged fontanels. The onset of oligohydramnios is delayed and variable, normally later than 22 weeks of gestation, conditioning variation in the expression of the other deformities. We report 2 cases of renal tubular dysgenesis occurring in a non-consanguineous couple.

Renal tubular dysgenesis, a not uncommon autosomal recessive disorder leading to oligohydramnios: Role of the Renin-Angiotensin system

Renal tubular dysgenesis is a clinical disorder that is observed in fetuses and characterized by the absence or poor development of proximal tubules, early onset and persistent oligohydramnios that leads to the Potter sequence, and skull ossification defects. It may be acquired during fetal development or inherited as an autosomal recessive disease. It was shown recently that autosomal recessive renal tubular dysgenesis is genetically heterogeneous and linked to mutations in the genes that encode components of the renin-angiotensin system. This study analyzed the clinical expression of the disease in 29 fetus/neonates from 18 unrelated families and evaluated changes in renal morphology and expression of the renin-angiotensin system. The disease was uniformly severe, with perinatal death in all cases as a result of persistent anuria and hypoxia related to pulmonary hypoplasia. Severe defects in proximal tubules were observed in all fetuses from 18 gestational weeks onward, and lesions also involved other tubular segments. They were associated with thickening of the renal arterial vasculature, from the arcuate to the afferent arteries. Renal renin expression was strikingly increased in 19 of 24 patients studied, from 13 families, whereas no renal renin was detected in four patients from three families. Angiotensinogen and angiotensin-converting enzyme were absent or present in only small amounts in the proximal tubule, in correlation with the severity of tubular abnormalities. No specific changes were detected in angiotensin II receptor expression. The severity and the early onset of the clinical and pathologic expression of the disease underline the major importance of this system in fetal kidney function and development in humans. The identification of the disease on the basis of precise histologic analysis and the research of the genetic defect now allow genetic counseling and early prenatal diagnosis.

Mutations in genes in the renin-angiotensin system are associated with autosomal recessive renal tubular dysgenesis

Autosomal recessive renal tubular dysgenesis is a severe disorder of renal tubular development characterized by persistent fetal anuria and perinatal death, probably due to pulmonary hypoplasia from early-onset oligohydramnios (Potter phenotype). Absence or paucity of differentiated proximal tubules is the histopathological hallmark of the disease and may be associated with skull ossification defects. We studied 11 individuals with renal tubular dysgenesis, belonging to nine families, and found that they had homozygous or compound heterozygous mutations in the genes encoding renin, angiotensinogen, angiotensin converting enzyme or angiotensin II receptor type 1. We propose that renal lesions and early anuria result from chronic low perfusion pressure of the fetal kidney, a consequence of renin-angiotensin system inactivity. This is the first identification to our knowledge of a renal mendelian disorder linked to genetic defects in the renin-angiotensin system, highlighting the crucial role of the renin-angiotensin system in human kidney development.

A gammaGT-AT1A receptor transgene protects renal cortical structure in AT1 receptor-deficient mice

To understand the physiological role of angiotensin type 1 (AT(1)) receptors in the proximal tubule of the kidney, we generated a transgenic mouse line in which the major murine AT(1) receptor isoform, AT(1A), was expressed under the control of the P1 portion of the gamma-glutamyl transpeptidase (gammaGT) promoter. In transgenic mice, this promoter has been shown to confer cell-specific expression in epithelial cells of the renal proximal tubule. To avoid random integration of multiple copies of the transgene, we used gene targeting to produce mice with a single-copy transgene insertion at the hypoxanthine phosphoribosyl transferase (Hprt) locus on the X chromosome. The physiological effects of the gammaGT-AT(1A) transgene were examined on a wild-type background and in mice with targeted disruption of one or both of the murine AT(1) receptor genes (Agtr1a and Agtr1b). On all three backgrounds, gammaGT-AT(1A) transgenic mice were healthy and viable. On the wild-type background, the presence of the transgene did not affect development, blood pressure, or kidney structure. Despite relatively low levels of expression in the proximal tubule, the transgene blunted the increase in renin expression typically seen in AT(1)-deficient mice and partially rescued the kidney phenotype associated with Agtr1a(-/-)Agtr1b(-/-) mice, significantly reducing cortical cyst formation by more than threefold. However, these low levels of cell-specific expression of AT(1) receptors in the renal proximal tubule did not increase the low blood pressures or abolish sodium sensitivity, which are characteristic of AT(1) receptor-deficient mice. Although our studies do not clearly identify a role for AT(1) receptors in the proximal tubules of the kidney in blood pressure homeostasis, they support a major role for these receptors in modulating renin expression and in maintaining structural integrity of the renal cortex.

Renal tubular dysgenesis in an hydropic fetus with trisomy 21: a case report with literature review

Renal tubular dysgenesis (RTD) is a rare form of noncystic renal disease characterized by paucity or absence of proximal renal tubules. Always lethal in the perinatal period, it has been associated with Potter sequence and with other congenital malformations. An autosomal recessive inheritance has been suggested. We present a case of renal tubular dysgenesis associated with fetal hydrops and trisomy 21, with a review of relevant literature.

The role of ACE2 in cardiovascular physiology

The renin-angiotensin system (RAS) is critically involved in cardiovascular and renal function and in disease conditions, and has been shown to be a far more complex system than initially thought. A recently discovered homologue of angiotensin-converting enzyme (ACE)--ACE2--appears to negatively regulate the RAS. ACE2 cleaves Ang I and Ang II into the inactive Ang 1-9 and Ang 1-7, respectively. ACE2 is highly expressed in kidney and heart and is especially confined to the endothelium. With quantitative trait locus (QTL) mapping, ACE2 was defined as a QTL on the X chromosome in rat models of hypertension. In these animal models, kidney ACE2 messenger RNA and protein expression were markedly reduced, making ACE2 a candidate gene for this QTL. Targeted disruption of ACE2 in mice failed to elicit hypertension, but resulted in severe impairment in myocardial contractility with increased angiotensin II levels. Genetic ablation of ACE in the ACE2 null mice rescued the cardiac phenotype. These genetic data show that ACE2 is an essential regulator of heart function in vivo. Basal renal morphology and function were not altered by the inactivation of ACE2. The novel role of ACE2 in hydrolyzing several other peptides-such as the apelin peptides, opioids, and kinin metabolites-raises the possibility that peptide systems other than angiotensin and its derivatives also may have an important role in regulating cardiovascular and renal function.

Renal tubular dysgenesis (RTD) - an important cause of the oligohydramnion-sequence. Report of 3 cases and review of the literature

Renal tubular dysgenesis (RTD) is a disorder characterized by neonatal renal failure and regular gross renal architecture, although the histological features of immature and shortened proximal tubules lead to neonatal death. The pathogenesis of this condition includes a congenital familial condition, a twin-twin transfusion syndrome, and an angiotensin-converting enzyme inhibitor intake by the mother. The clinical picture shows an association with oligohydramnia, pulmonary hypoplasia, and skull ossification defects. In the present paper, we report the occurrence of RTD in three infants of a consanguinous couple and compared our data with those of the literature. Our data confirm that late second trimester demonstration of oligohydramnion, with structurally normal kidneys and with or without skull ossification defects, allows the diagnosis of renal tubular dysgenesis, which, however, has to be confirmed by histological and immunohistological examinations of the kidney.

Renal tubular dysgenesis-like lesions and hypocalvaria. Report of two cases involving indomethacin

We describe a case of twins with twin-to-twin transfusion syndrome (TTS) who were found to have renal tubular dysgenesis (TRD)-like lesions and hypocalvaria attributed to indomethacin treatment of the mother for acute polyhydramnios. History of pregnancy, postnatal clinical course, pathological findings of the kidneys, and the skulls are presented and discussed. These findings include incompletely differentiated proximal tubules in the kidneys and hypoplastic calvaria in both twins. The renal tubular lesions were more marked in the donor than in the transfused twin, probably due to the greater degree of ischemia in that twin. This seems to be in favor of a vascular etiology of the renal defects. However, the fact that similar renal lesions and hypocalvaria were also present in the transfused twin seems to indicate that indomethacin played a role in their onset. This so-called kidney-skull connection has never been reported in conjunction with indomethacin therapy.