The impact of small kidneys

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.

Distinguishing Features of Childhood Renal Dysplasia

BACKGROUND

Renal dysplasia (RD) is a major cause of chronic kidney disease (CKD) in childhood. Herein, we present a single-center experience about distinctive features of different subtypes of dysplasia.

METHODS

All children with RD admitted between January 2018 and June 2019 were included in this cross-sectional study. Patients were classified as having unilateral RD, bilateral RD, posterior urethral valves (PUV), and multicystic-dysplastic kidneys (MCDK).

RESULTS

A total of 198 patients (108 unilateral RD, 31 bilateral RD, 16 PUV, and 43 MCDK) with a follow-up period of 80 (1.5-240) months were included. The overall consanguinity rate was 22%, whereas it was 56% in bilateral RD patients. Two-thirds had additional urogenital anomalies. Hypertension was detected in 16% of the patients, and 20% had median proteinuria of 16 (5.2-173) mg/m2/h, which was significantly higher in the PUV and bilateral RD groups. The overall rate of CKD was 23%, which was more frequent in bilateral RD and PUV groups. The median age at end-stage renal disease was 91.5 (0.5-208) months, including 12 renal transplant patients.

CONCLUSIONS

As different subtypes of RD have distinct clinical and prognostic features, the follow-up of RD patients should be individualized, and modifiable complications such as proteinuria and HT should be monitored closely.

Pediatric Bilateral Hypoplastic Kidney Complicated With C1q Nephropathy: A Case Report

Progressive kidney dysfunction is often observed in children with bilateral hypoplastic kidneys. While glomerulopathy can exacerbate hypoplastic kidney progression, only IgA nephropathy and post-streptococcal acute glomerulonephritis have been noted in such cases. Herein, we present a case of a four-year-old female patient with bilateral hypoplastic kidney, kidney dysfunction, and significant proteinuria (urinary protein/creatinine ratio > 1 g/gCr), prompting referral owing to persistent hematuria since two years of age. Enalapril was initiated; however, urinary findings exhibited no improvement despite stable symptoms and kidney function. Subsequently, a kidney biopsy was performed at six years of age, and C1q nephropathy was diagnosed. Given the presence of only mild mesangial proliferation, steroids were not administered; enalapril treatment was continued. By seven years of age, the patient's hematuria had resolved, and proteinuria levels had decreased. On the latest follow-up at 12 years of age, kidney function was preserved with only mild proteinuria. This case report highlights the favorable prognosis of asymptomatic C1q nephropathy characterized by mild mesangial proliferation, even in patients with hypoplastic kidneys, renal dysfunction, and significant proteinuria. It emphasizes the significance of timely pathological evaluation for guiding appropriate interventions in such patients.

Hypertension in children with congenital anomalies of the kidney and urinary tract

BACKGROUND

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most common cause of childhood chronic kidney disease (CKD). We hypothesized that hypertension varies across CAKUT categories and increases the risk of CKD.

METHODS

This was a retrospective cohort study and included cases with a multicystic dysplastic kidney (MCDK, n = 81), unilateral kidney agenesis (UKA, n = 47), kidney hypoplasia (KH, n = 130), and posterior urethral valves (PUV, n = 75). Hypertension was defined as systolic or diastolic blood pressure ≥ 95th percentile for age, sex and height, and CKD as an estimated glomerular filtration rate < 60 ml/min/1.73 m2, both at 2 consecutive clinic visits at least 3 months apart.

RESULTS

Sixty-two (19%) out of 333 cases developed hypertension, with significant difference according to CAKUT type. Patients with smaller kidney size (7.7 vs. 8.3, p = 0.045), kidney anomalies in addition to the primary diagnosis (aCAKUT) (53 vs. 38%, p = 0.03), proteinuria (46 vs. 12%, p < 0.001), and CKD (51 vs. 23%, p < 0.001) were more likely to develop hypertension. When adjusted for kidney size, the diagnoses of PUV (OR 10.9, 95%CI 3.0, 40.5), UKA (OR 6.4, 95%CI 1.6, 24.9) and KH (OR 4.2, 95%CI 1.1, 16.1), and aCAKUT (OR 2.1, 95%CI 1.2, 3.9) were independent risk factors for hypertension. Hypertension increased the risk of developing CKD by twofold (HR 1.9, 95%CI 1.19, 2.94).

CONCLUSION

Hypertension is common in children with CAKUT and increases the risk of CKD. These findings will aid in the development of a standardized clinical pathway for the care of hypertensive children with CAKUT.

Congenital anomalies of the kidney and urinary tract: defining risk factors of disease progression and determinants of outcomes

Congenital anomalies of the kidney and urinary tract (CAKUT) result from disruptions in normal kidney and urinary tract development during fetal life and collectively represent the most common cause of kidney failure in children worldwide. The antenatal determinants of CAKUT are diverse and include mutations in genes responsible for normal nephrogenesis, alterations in maternal and fetal environments, and obstruction within the normal developing urinary tract. The resultant clinical phenotypes are complex and depend on the timing of the insult, the penetrance of underlying gene mutations, and the severity and timing of obstruction related to the sequence of normal kidney development. Consequently, there is a broad spectrum of outcomes for children born with CAKUT. In this review, we explore the most common forms of CAKUT and those most likely to develop long-term complications of their associated kidney malformations. We discuss the relevant outcomes for the different forms of CAKUT and what is known about clinical characteristics across the CAKUT spectrum that are risk factors of long-term kidney injury and disease progression.

Predicting outcomes in children with congenital anomalies of the kidney and urinary tract

BACKGROUND

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most frequent causes of childhood chronic kidney disease (CKD). Using a large CAKUT cohort, we sought to identify the predictors of CKD and to develop a prediction model that informs a risk-stratified clinical pathway.

METHODS

This was a retrospective cohort study including cases with multicystic dysplastic kidneys (MCDK), unilateral kidney agenesis (UKA), kidney hypoplasia (KH), and posterior urethral valves (PUV). We identified risk factors for CKD (estimated glomerular filtration rate [eGFR] <60 ml/min/1.73 m2) and tested their performance in an adjusted multivariate binary regression model. Prediction probability scores for CKD were used to separate cases likely to develop complications from those not needing specialist follow-up.

RESULTS

We identified 452 eligible cases of CAKUT with 22% developing CKD. Strongest associations with CKD included primary diagnosis (OR 3.5, 95% CI 2.6-4.6), preterm delivery (OR 2.3, 95% CI 1.2-4.4), non-kidney anomalies (OR 1.8, 95% CI 1.1-3), first eGFR<90 (OR 8.9, 95% CI 4.4-18.1), small kidney size (OR 9, 95% CI 4.9-16.6), and additional kidney anomalies (OR 1.6, 95% CI 1.2-2.8). PUV (OR 4.7, 95% CI 1.5-15.3), first eGFR <90 (OR 4.4, 95% CI 2-9.7), and kidney length to body length ratio <7.9 (OR 4.2, 95% CI 1.9-9.2) were independent predictors of CKD. The regression model had a prediction accuracy of 80% and a prediction probability c-statistic of 0.81.

CONCLUSION

Using a large combined CAKUT cohort we identified risk factors for CKD. Our prediction model provides the first steps towards a risk-stratified clinical pathway. A higher resolution version of the Graphical abstract is available as Supplementary information.

Kidney length standardized to body length predicts outcome in infants with a solitary functioning kidney

BACKGROUND

Infants with a solitary functioning kidney (SFK) are at risk for chronic kidney injury (CKI). Lack of compensatory kidney growth (CKG) is associated with CKI, but measuring CKG is challenging since it is typically reported relative to normal kidneys. This study aims to (1) standardize SFK growth in infants, (2) investigate the relationship between standardized kidney length and clinical outcomes, and (3) use these results to develop a risk-based prediction model and local clinical pathway for SFK care.

METHODS

This was a quality improvement study of 166 infants with an SFK. Linear regression was used to assess kidney growth from 0 to 180 days of life. Univariate binary regression analysis was used to identify kidney length to body length thresholds associated with the development of CKI, defined as the composite outcome of chronic kidney disease (eGFR < 60 mL/min/1.73 m²), hypertension, or proteinuria.

RESULTS

Kidneys grew in length from 0 to 180 days, and growth was constant when standardized to body length. Over follow-up, infants with a baseline kidney length to body length ≤ 0.088 were more likely to experience CKI than the rest of the cohort (27 vs. 8%, p = 0.04). Kidney length to body length ≤ 0.088 was also significantly associated with CKI development (OR 4.17, 95% CI 1.14-15.28, p = 0.04).

CONCLUSIONS

In this study, kidney length to body length ratio was a stable CKG metric over 0-180 days, and a baseline ratio ≤ 0.088 was a risk factor for CKI. Results will aid in developing a practical, point-of-care risk assessment tool, and overarching risk-stratified clinical pathway for infants with an SFK. A higher resolution version of the Graphical abstract is available as Supplementary information.

Unilateral hypoplastic kidney in adults: An experience of a tertiary-level urology center

BACKGROUND

Unilateral small-sized kidney is a radiological term referring to both the congenital and acquired causes of reduced kidney volume. However, the hypoplastic kidney may have peculiar clinical and radiological characterizations.

AIM

To evaluate the clinical presentations, complications, and management approaches of the radiologically diagnosed unilateral hypoplastic kidney.

METHODS

A retrospective review of the records of patients with a radiological diagnosis of unilateral hypoplastic kidney between July 2015 and June 2020 was done at Assiut Urology and Nephrology Hospital, Assiut University, Egypt.

RESULTS

A total of 33 cases were diagnosed to have unilateral hypoplastic kidney with a mean (range) age of 39.5 ± 11.2 (19-73) years. The main clinical presentation was loin pain (51.5%), stone passer (9.1%), anuria (12.1%), accidental discovery (15.2%), or manifestations of urinary tract infections (12.1%). Computed tomography was the most useful tool for radiological diagnosis. However, radioisotope scanning could be requested for verification of surgical interventions and nephrectomy decisions. Urolithiasis occurred in 23 (69.7%) cases and pyuria was detected in 22 (66.7%) cases where the infection was documented by culture and sensitivity test in 19 cases. While the non-complicated cases were managed by assurance only (12.1%), nephrectomy (15.2%) was performed for persistent complications. However, symptomatic (27.3%) and endoscopic (45.6%) approaches were used for the management of correctable complications.

CONCLUSION

Unilateral hypoplastic kidney in adults has various complications that range from urinary tract infections to death from septicemia. Diagnosis is mainly radiological and management is usually conservative or minimally invasive.

Outcomes of solitary functioning kidneys-renal agenesis is different than multicystic dysplastic kidney disease

BACKGROUND

Multicystic dysplastic kidney (MCDK) disease and unilateral renal agenesis (URA) are well-known causes of a solitary functioning kidney (SFK) and are associated with long-term kidney injury. The aims of this study were to characterize the natural history of SFK at our center, define the risk factors associated with chronic kidney injury, and identify distinguishing features between URA and MCDK that predict outcome.

METHODS

This was a retrospective cohort study of 230 SFK patients. We compared MCDK (n=160) and URA (n=70) according to clinical features at diagnosis and kidney outcomes over follow-up. Univariate and multivariate binary regression analysis was used to determine independent risk factors for chronic kidney injury, defined as the composite outcome of hypertension, proteinuria, or chronic kidney disease (eGFR <60 mL/min/1.73m²).

RESULTS

URA had a higher prevalence of comorbid genetic syndromes (15 vs. 6%, p=0.04), non-renal anomalies (39 vs. 11%, p<0.001), and congenital anomalies of the kidney and urinary tract (CAKUT) (51 vs. 26%, p<0.001) than MCDK. Over follow-up, URA experienced more hypertension (19 vs. 3%, p=0.002), proteinuria (12 vs. 3%, p=0.03), and the composite outcome (19 vs. 6%, p=0.003) than MCDK. Independent risk factors for chronic kidney injury included CAKUT (OR 5.01, p=0.002) and URA (OR 2.71, p=0.04).

CONCLUSIONS

In our population, URA was more likely to have associated syndromes or anomalies, and to have worse outcomes over time than MCDK. URA diagnosis was an independent risk factor for chronic kidney injury. Our results will be used to develop a standardized clinical pathway for SFK management. A higher resolution version of the Graphical abstract is available as Supplementary information.

Primary causes of kidney disease and mortality in dialysis-dependent children

BACKGROUND

Congenital anomalies of the kidney and urinary tract (CAKUT) is associated with a slower progression to end-stage renal disease (ESRD) in pre-dialysis patients. However, little is known about the associated mortality risks after transitioning to dialysis.

METHODS

This retrospective cohort study included 0-21 year-old incident dialysis patients from the United States Renal Data System starting dialysis between 1995 and 2016. We examined the association of CAKUT vs. non-CAKUT with all-cause mortality, using Cox regression adjusted for case mix variables. We also examined the mortality risk associated with 14 non-CAKUT vs. CAKUT ESRD etiologies and under stratification by estimated glomerular filtration rate (eGFR).

RESULTS

Among 25,761 patients, the median (interquartile range) age was 17 (11-19) years, and 4780 (19%) had CAKUT. CAKUT was associated with lower mortality, with an adjusted hazard ratio (aHR) of 0.72 (95%CI, 0.64-0.81) (reference: non-CAKUT). In age-stratified analyses, CAKUT vs. non-CAKUT aHRs (95%CI) were 0.66 (0.54-0.80), 0.56 (0.39-0.80), 0.66 (0.50-0.86), and 0.97 (0.80-1.18) among patients < 6, 6-< 13, 13-< 18, and ≥ 18 years at dialysis initiation, respectively. Among non-CAKUT ESRD etiologies, the risk of mortality associated with primary glomerulonephritis (aHR, 0.93; 95%CI 0.80-1.09) and focal segmental glomerulosclerosis (aHR, 0.89; 95%CI, 0.75-1.04) were comparable or slightly lower compared to CAKUT, whereas most other primary causes were associated with higher mortality risk. While the CAKUT group had lower mortality risk compared to the non-CAKUT group patients with eGFR ≥5 mL/min/1.73m², CAKUT was associated with higher mortality in patients with eGFR < 5 mL/min/1.73 m².

CONCLUSIONS

CAKUT is associated with lower mortality among children < 18 years old, but showed comparable mortality with non-CAKUT among patients ≥ 18 years old. ESRD etiology should be considered in risk assessment for children initiating dialysis.

Survival and Kidney Outcomes of Children with an Early Diagnosis of Posterior Urethral Valves

BACKGROUND AND OBJECTIVES

Posterior urethral valve is the most common cause of bladder outlet obstruction in infants. We aimed to describe the rate and timing of kidney-related and survival outcomes for children diagnosed with posterior urethral valves in United States children's hospitals using the Pediatric Health Information System database.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This retrospective cohort study included children hospitalized between January 1, 1992 and December 31, 2006, who were in their first year of life, had a diagnosis of congenital urethral stenosis, and underwent endoscopic valve ablation or urinary drainage intervention, or died. Records were searched up to December 31, 2018 for kidney-related mortality, placement of a dialysis catheter, and kidney transplantation. Cox regression analysis was used to identify risk factors, and Kaplan-Meier survival analysis used to determine time-to-event probability. Subgroup survival analysis was performed with outcomes stratified by the strongest identified risk factor.

RESULTS

Included were 685 children hospitalized at a median age of 7 (interquartile range, 1-37) days. Thirty four children (5%) died, over half during their initial hospitalization. Pulmonary hypoplasia was the strongest risk factor for death (hazard ratio, 7.5; 95% confidence interval [95% CI], 3.3 to 17.0). Ten-year survival probability was 94%. Fifty-nine children (9%) underwent one or more dialysis catheter placements. Children with kidney dysplasia had over four-fold risk of dialysis catheter placement (hazard ratio, 4.6; 95% CI, 2.6 to 8.1). Thirty-six (7%) children underwent kidney transplant at a median age of 3 (interquartile range, 2-8) years. Kidney dysplasia had a nine-fold higher risk of kidney transplant (hazard ratio, 9.5; 95% CI, 4.1 to 22.2).

CONCLUSIONS

Patients in this multicenter cohort with posterior urethral valves had a 5% risk of death, and were most likely to die during their initial hospitalization. Risk of death was higher with a diagnosis of pulmonary hypoplasia. Kidney dysplasia was associated with a higher risk of need for dialysis/transplant.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2019_10_03_CJN04350419.mp3.

The population-based prevalence of albuminuria in children

OBJECTIVES

To determine the population-based prevalence of albuminuria in Australian children and validate any negative correlation with body mass index (BMI).

METHODS

Data from the Australian Health Survey 2011-2013 were used. This is a large-scale survey of the health of the Australian population, conducted by the Australian Bureau of Statistics, and uses a stratified, multistage area design with replicate weights attached to observations to allow for the derivation of accurate population estimates. We considered children aged 5-18 years, and defined albuminuria as an albumin-to-creatinine ratio (ACR) >30 mg/g (3.4 mg/mmol).

RESULTS

A total of 975 children provided urine samples for determination of ACR. The prevalence of albuminuria was 10.2% for males (95% confidence interval [CI] 6.1-14.2) and 15.5% for females (95% CI 10.7-20.3). After adjusting for age and gender, the odds ratio for albuminuria associated with being overweight or obese was 0.34 (95% CI 0.15-0.75). This relationship also held for waist-to-height ratio, where the adjusted odds ratio for each 0.1 increase was 0.46 (95% CI 0.26-0.82).

CONCLUSIONS

Albuminuria, using a measurement suitable for population-based and clinical screening, occurs in 12.8% of school-aged Australian children, and is less common in overweight and obese children.