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

Congenital Anomalies of the Kidney and Urinary Tract in Down Syndrome: Prevalence, Phenotypes, Genetics and Clinical Management

Down syndrome (DS), the most common survivable autosomal aneuploidy, is associated with a high prevalence of congenital anomalies of the kidney and urinary tract (CAKUT), significantly increasing the risk of chronic kidney disease (CKD). This review examines the diversity of CAKUT phenotypes reported in individuals with DS, focusing on anomalies affecting the kidney, ureter, bladder, and urethra. According to available literature, hydronephrosis is the most common renal anomaly, often secondary to other CAKUT phenotypes, followed by renal hypoplasia and glomerulocystic disease. Furthermore, obstructive uropathies are also frequent but usually lack detailed characterization in the literature. Key features of CAKUT in DS, including reduced kidney size, renal cystic diseases, acquired glomerulopathies, reduced nephron number, and immature glomeruli heighten the risk of CKD. Also, early detection of lower urinary tract dysfunction (LUTD) is critical to prevent progressive upper urinary tract damage and CKD. Despite the prevalence of CAKUT in DS, reported between 0.22% and 21.16%, there is a lack of standardized diagnostic criteria, consistent terminology, and extended follow-up studies. Systematic screening from infancy, including regular renal monitoring via urinalysis and ultrasound, plays a critical role in the timely diagnosis and intervention of CAKUT. To further enhance diagnostic accuracy and develop effective therapeutic strategies, increased awareness and focused research into the genetic factors underlying these anomalies are essential. Moreover, a multidisciplinary approach is indispensable for managing CAKUT and its associated complications, ultimately ensuring better long-term outcomes and an improved quality of life for individuals with DS.

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.

Increased prevalence of renal and urinary tract anomalies in children with Down syndrome

OBJECTIVE

The goal was to investigate the prevalence of renal and urinary tract anomalies (RUTAs) in a Down syndrome (DS) population.

METHODS

Data were obtained from the New York State Congenital Malformation Registry (NYS-CMR) in this retrospective cohort study. The occurrence of RUTAs was assessed for children with and without DS who were born in NYS between 1992 and 2004. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated for each malformation.

RESULTS

Between 1992 and 2004, 3832 children with DS and 3 411 833 without DS were born in NYS. The prevalence of RUTAs in the DS population was 3.2%, compared with 0.7% in the NYS population (OR: 4.5 [95% CI: 3.8 -5.4]). Children with DS had significantly increased risks of anterior urethral obstruction (OR: 29.7 [95% CI: 4.0 -217.7]), cystic dysplastic kidney (OR: 4.5 [95% CI: 1.5-14.1]), hydronephrosis (OR: 8.7 [95% CI: 6.8 -11.0]), hydroureter (OR: 8.5 [95% CI: 3.5-20.4]), hypospadias (OR: 2.0 [95% CI: 1.4 -2.9]), posterior urethral valves (OR: 7.1 [95% CI: 1.8 -28.8]), prune belly syndrome (OR: 11.9 [95% CI: 1.6 - 85.4]), and renal agenesis (OR: 5.4 [95% CI: 2.8 -10.4]). There was no significantly increased risk of ectopic kidney (OR: 1.6 [95% CI: 0.2-11.2]) or ureteropelvic junction obstruction (OR: 1.4 [95% CI: 0.2-9.9]) in the DS population.

CONCLUSION

Children with DS have significantly increased risks of RUTAs.

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.

Renal biopsy in congenital ureteropelvic junction obstruction: evidence for parenchymal maldevelopment

The renal histologic changes associated with congenital ureteropelvic junction obstruction (UPJO) and the relationship to clinical imaging have not been well studied. In order to better understand the histologic alterations of congenital UPJO and their relationship with clinical imaging and outcomes, we examined renal biopsies from 61 patients undergoing pyeloplasty for congenital UPJO. Glomeruli were analyzed for various injury patterns and the tubulointerstitium was examined for tubular atrophy/simplification and fibrosis. Two methods were used to evaluate tubular mass: glomerular density and morphometric measurement of tubular size and density. Control specimens were obtained from age-matched autopsy specimens without renal pathology. Glomerular changes were identified in 73% of all biopsies and were present in a range from 1.7 to 91% of glomeruli in each patient. Overt tubulointerstitial changes were present in 26% of all biopsies. Fibrosis was noted to occur with tubulointerstitial changes in a significantly greater fraction of children over the age of 1 year (P=0.026). Increased glomerular density was associated with severe hydronephrosis (P<0.02). Normal glomerular density was inversely correlated with age (P<0.001), but this relationship was more variable in UPJO (P<0.01). Among patients with intact differential function preoperatively (>45%), postoperative functional decline was predicted only by increased glomerular density. 20 biopsies without overt tubulointerstitial changes were analyzed morphometrically and showed a significant reduction in proximal tubular (PT) size, but unchanged density. Distal tubular (DT) size was unchanged in UPJO, but density was increased. The PT/DT ratio was therefore markedly decreased in UPJO (P<0.0001). Both PT and DT sizes were significantly larger in children with a diuretic renogram washout time less than 20 min than those with greater than 20 min, a common threshold for functionally significant obstruction (P<0.05). Capsular thickness was significantly increased in UPJO. In all, 36% of biopsies had a thickness >0.5 mm and this was associated with greater degrees of tubulointerstitial changes and glomerular alterations. Congenital UPJO produces a variety of renal parenchymal changes, which may in part reflect abnormal development. Some of these alternations are seen in clinical imaging and may help predict outcomes, but there is significant discordance between conventional imaging and histological findings.