Effects of maternal vitamin A status on kidney development: a pilot study

Practical Approach to Congenital Anomalies of the Kidneys: Focus on Anomalies With Insufficient or Abnormal Nephron Development: Renal Dysplasia, Renal Hypoplasia, and Renal Tubular Dysgenesis

Congenital anomalies of the kidney and urinary tract (CAKUT) accounts for up to 30% of antenatal congenital anomalies and is the main cause of kidney failure in children worldwide. This review focuses on practical approaches to CAKUT, particularly those with insufficient or abnormal nephron development, such as renal dysplasia, renal hypoplasia, and renal tubular dysgenesis. The review provides insights into the histological features, pathogenesis, mechanisms, etiologies, antenatal and postnatal presentation, management, and prognosis of these anomalies. Differential diagnoses are discussed as several syndromes may include CAKUT as a phenotypic component and renal dysplasia may occur in some ciliopathies, tumor predisposition syndromes, and inborn errors of metabolism. Diagnosis and genetic counseling for CAKUT are challenging, due to the extensive variability in presentation, genetic and phenotypic heterogeneity, and difficulties to assess postnatal lung and renal function on prenatal imaging. The review highlights the importance of perinatal autopsy and pathological findings in surgical specimens to establish the diagnosis and prognosis of CAKUT. The indications and the type of genetic testing are discussed. The aim is to provide essential insights into the practical approaches, diagnostic processes, and genetic considerations offering valuable guidance for pediatric and perinatal pathologists.

Untargeted Maternal Plasma Metabolomics in Hirschsprung Disease: A Pilot Study

Background and Aims

Hirschsprung disease (HSCR) is a congenital disorder of unknown etiology affecting the enteric nervous system (ENS). Since the early gestational development of the ENS is dependent on the prenatal maternal metabolic environment, the objective of this pilot study was to explore the role of specific maternal plasma metabolites in the etiology of HSCR.

Methods

In this cross-sectional study, postnatal (as a surrogate for prenatal) plasma samples were obtained from mothers of children diagnosed with HSCR (n = 7) and age-matched mothers of normal children (n = 6). The plasma metabolome was analyzed by ultra-high-pressure liquid chromatography and mass spectrometry. Metabolites were identified by mzCloud using Compound Discoverer software. Using an untargeted metabolomics workflow, metabolites with case versus control group differences were identified.

Results

A total of 268 unique plasma metabolites were identified and annotated in maternal plasma. Of these, 57 were significantly different between case and control groups (P < 0.05, t-test). Using a false discovery rate corrected cutoff of 10% to adjust for multiple comparisons, 19 metabolites were significantly different in HSCR cases, including carnitines, medium-chain fatty acids, and glutamic acid. Pathways affected were for amino acid and lipid metabolism.

Conclusion

Disordered prenatal metabolic pathways may be involved in the etiopathogenesis of HSCR in the developing fetus. This is the first study to assess maternal plasma metabolomics in HSCR.

The function of miRNAs in the process of kidney development

MicroRNAs (miRNAs) are a class of small non-coding RNAs (ncRNAs) that typically consist of 19-25 nucleotides in length. These molecules function as essential regulators of gene expression by selectively binding to complementary target sequences within messenger RNA (mRNA) molecules, consequently exerting a negative impact on gene expression at the post-transcriptional level. By modulating the stability and translation efficiency of target mRNAs, miRNAs play pivotal roles in diverse biological processes, including the intricate orchestration of organ development. Among these processes, the development of the kidney has emerged as a key area of interest regarding miRNA function. Intriguingly, recent investigations have uncovered a subset of miRNAs that exhibit remarkably high expression levels in the kidney, signifying their close association with kidney development and diseases affecting this vital organ. This growing body of evidence strongly suggests that miRNAs serve as crucial regulators, actively shaping both the physiological processes governing kidney function and the pathological events leading to renal disorders. This comprehensive review aims to provide an up-to-date overview of the latest research progress regarding miRNAs and their involvement in kidney development. By examining the intricate interplay between miRNAs and the molecular pathways driving kidney development, this review seeks to elucidate the underlying mechanisms through which miRNAs exert their regulatory functions. Furthermore, an in-depth exploration of the role played by miRNAs in the occurrence and progression of renal dysplasia will be presented. Renal dysplasia represents a significant developmental anomaly characterized by abnormal kidney tissue formation, and miRNAs have emerged as key players in this pathological process. By shedding light on the intricate network of miRNA-mediated regulatory mechanisms involved in kidney dysplasia, this review aims to provide valuable insights for the diagnosis and research of diseases associated with aberrant kidney development.

Sex difference and risk factors in burden of urogenital congenital anomalies from 1990 to 2019

Urogenital congenital anomalies (UCAs) is defined as "any live-birth with a urinary or genital condition" and affects millions of men and women worldwide. However, sex differences and related environmental risk factors in UCAs burden on a global scale have not been assessed. Using data from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019, we estimated prevalence, incidence, mortality and disability-adjusted life years (DALYs) of UCAs from 1990 to 2019 by sex, region, and socio-demographic Index (SDI) in 204 countries and territories. The disease burden of UCAs was also estimated attributable to each risk factor were estimated according to risk exposure. In 2019, UCAs caused 10,200 all-ages deaths (95% UI 7550-13,400). The combined global incidence rate was 8.38 per 1000 (95% UI 5.88-12.0) live births. The ASIR increased slightly, while the ASDR decreased from 1990 to 2019.The UCAs burden varies greatly depending on the development level and geographical location. The UCAs burden was significantly higher in men than in women, and the sex differences showed an enlarging trend. Health risks and issues, including pollution, child and maternal malnutrition, diet habits, unsafe sanitation and water source, were detected to be positively related to UCAs burden. Albeit the age-standardised prevalence, mortality, incidence, and DALYs of UCAs have decreased, they still cause a public health challenge worldwide. The high deaths and DALYs rates in low and low-middle SDI countries highlight the urgent need for improved preventive, diagnostic, and therapeutic measures. Global strategies for enhancing water safety, reducing pollution, and healthy diets are crucial steps in reducing the burden of UCAs.

Clinical and pathological investigation of oligomeganephronia

BACKGROUND

Oligomeganephronia (OMN) is a rare congenital anomaly involving the kidney and urinary tract, characterized by decreased number and compensatory hypertrophy of the nephron. It is caused by abnormal kidney development during the embryonic period, especially in patients with low birth weight; however, the actual etiology and clinical features remain unknown. We aim to reveal the clinical and pathological characteristics, treatment, and outcome.

METHODS

Ten patients diagnosed with OMN between 2013 and 2020 were retrospectively investigated. The data were presented as the median ± interquartile range, and statistical significance was set at p < 0.05.

RESULTS

The age at diagnosis was 14.1 years, the male-to-female ratio was 6:4, and only four cases were born with low birth weight. The estimated glomerular filtration rate (eGFR) was 62.2 mL/min/1.73 m2. The glomerulus diameter of OMN patients was significantly larger (217 vs. 154 µm, p < 0.001) in OMN patients, and the number of glomeruli of OMN patients was lower (0.89 vs. 2.05/mm2, p < 0.001) than the control group. Eight of the ten cases were identified by urinary screening. Nine patients were treated with renin-angiotensin system (RAS) inhibitors, following which proteinuria successfully decreased or disappeared. Their median eGFR was also stable, 53.3 mL/min/1.73 m2.

CONCLUSIONS

As few symptoms can lead to OMN discovery, most patients were found during urine screening at school. Kidney dysfunction was observed in all patients at the time of kidney biopsy. Proteinuria has been significantly reduced and the decline rate of eGFR might be improved by RAS inhibitors. "A higher resolution version of the Graphical abstract is available as Supplementary information".

Anatomy and embryology of congenital surgical anomalies: Congenital Anomalies of the Kidney and Urinary Tract

Congenital anomalies of the kidney and urinary tract or "CAKUT" describes a spectrum of developmental disorders with a range of associated clinical presentations and functional consequences. CAKUT underlies the majority of chronic kidney disease and kidney replacement therapy requirement in children, but functional deterioration can also emerge in adulthood. Understanding the normal embryological processes involved in kidney development allows us to appreciate the timing and sequence of critical events implicated when things go wrong. In this review, we will describe the normal developmental mechanisms and relate this to what we currently know about the pathological processes involved in various forms of CAKUT. We will also review the proposed etiological factors, in particular genetics, involved in CAKUT.

Regulation of nephron progenitor cell lifespan and nephron endowment

Low nephron number - resulting, for example, from prematurity or developmental anomalies - is a risk factor for the development of hypertension, chronic kidney disease and kidney failure. Considerable interest therefore exists in the mechanisms that regulate nephron endowment and contribute to the premature cessation of nephrogenesis following preterm birth. The cessation of nephrogenesis in utero or shortly after birth is synchronized across multiple niches in all mammals, and is coupled with the exhaustion of nephron progenitor cells. Consequently, no nephrons are formed after the cessation of developmental nephrogenesis, and lifelong renal function therefore depends on the complement of nephrons generated during gestation. In humans, a tenfold variation in nephron endowment between individuals contributes to differences in susceptibility to kidney disease; however, the mechanisms underlying this variation are not yet clear. Salient advances in our understanding of environmental inputs, and of intrinsic molecular mechanisms that contribute to the regulation of cessation timing or nephron progenitor cell exhaustion, have the potential to inform interventions to enhance nephron endowment and improve lifelong kidney health for susceptible individuals.

Nutrition Support Practices for Infants Born <750 Grams or <25 Weeks Gestation: A Call for More Research

With advances in medical care and efforts to care for continually smaller and younger preterm infants, the gestational age of viability has decreased, including as young as 21 or 22 weeks of gestation [...].

Liposoluble vitamins A and E in kidney disease

Kidney disease (KD) is characterized by the presence of elevated oxidative stress, and this is postulated as contributing to the high cardiovascular morbidity and mortality in these individuals. Chronic KD (CKD) is related to high grade inflammatory condition and pro-oxidative state that aggravates the progression of the disease by damaging primary podocytes. Liposoluble vitamins (vitamin A and E) are potent dietary antioxidants that have also anti-inflammatory and antiapoptotic functions. Vitamin deficits in CKD patients are a common issue, and multiple causes are related to them: Anorexia, dietary restrictions, food cooking methods, dialysis losses, gastrointestinal malabsorption, etc. The potential benefit of retinoic acid (RA) and α-tocopherol have been described in animal models and in some human clinical trials. This review provides an overview of RA and α tocopherol in KD.

Overlap of vitamin A and vitamin D target genes with CAKUT-related processes

Congenital Anomalies of the Kidney and Urinary Tract (CAKUT) are a group of abnormalities affecting the kidneys and their outflow tracts. CAKUT patients display a large clinical variability as well as a complex aetiology. Only 5% to 20% of the cases have a monogenic origin. It is thereby suspected that interactions of both genetic and environmental factors contribute to the disease. Vitamins are among the environmental factors that are considered for CAKUT aetiology. In this study, we aimed to investigate whether vitamin A or vitamin D could have a role in CAKUT aetiology. For this purpose we collected vitamin A and vitamin D target genes and computed their overlap with CAKUT-related gene sets. We observed limited overlap between vitamin D targets and CAKUT-related gene sets. We however observed that vitamin A target genes significantly overlap with multiple CAKUT-related gene sets, including CAKUT causal and differentially expressed genes, and genes involved in renal system development. Overall, these results indicate that an excess or deficiency of vitamin A might be relevant to a broad range of urogenital abnormalities.

Chronic Kidney Disease and Gut Microbiota: What Is Their Connection in Early Life?

The gut-kidney interaction implicating chronic kidney disease (CKD) has been the focus of increasing interest in recent years. Gut microbiota-targeted therapies could prevent CKD and its comorbidities. Considering that CKD can originate in early life, its treatment and prevention should start in childhood or even earlier in fetal life. Therefore, a better understanding of how the early-life gut microbiome impacts CKD in later life and how to develop ideal early interventions are unmet needs to reduce CKD. The purpose of the current review is to summarize (1) the current evidence on the gut microbiota dysbiosis implicated in pediatric CKD; (2) current knowledge supporting the impact of the gut-kidney axis in CKD, including inflammation, immune response, alterations of microbiota compositions, short-chain fatty acids, and uremic toxins; and (3) an overview of the studies documenting early gut microbiota-targeted interventions in animal models of CKD of developmental origins. Treatment options include prebiotics, probiotics, postbiotics, etc. To accelerate the transition of gut microbiota-based therapies for early prevention of CKD, an extended comprehension of gut microbiota dysbiosis implicated in renal programming is needed, as well as a greater focus on pediatric CKD for further clinical translation.

Premature differentiation of nephron progenitor cell and dysregulation of gene pathways critical to kidney development in a model of preterm birth

Preterm birth is a leading cause of neonatal morbidity. Survivors have a greater risk for kidney dysfunction and hypertension. Little is known about the molecular changes that occur in the kidney of individuals born preterm. Here, we demonstrate that mice delivered two days prior to full term gestation undergo premature cessation of nephrogenesis, resulting in a lower glomerular density. Kidneys from preterm and term groups exhibited differences in gene expression profiles at 20- and 27-days post-conception, including significant differences in the expression of fat-soluble vitamin-related genes. Kidneys of the preterm mice exhibited decreased proportions of endothelial cells and a lower expression of genes promoting angiogenesis compared to the term group. Kidneys from the preterm mice also had altered nephron progenitor subpopulations, early Six2 depletion, and altered Jag1 expression in the nephrogenic zone, consistent with premature differentiation of nephron progenitor cells. In conclusion, preterm birth alone was sufficient to shorten the duration of nephrogenesis and cause premature differentiation of nephron progenitor cells. These candidate genes and pathways may provide targets to improve kidney health in preterm infants.

The First Thousand Days: Kidney Health and Beyond

The global burden of chronic kidney disease (CKD) is rising. A superior strategy to advance global kidney health is required to prevent and treat CKD early. Kidney development can be impacted during the first 1000 days of life by numerous factors, including malnutrition, maternal illness, exposure to chemicals, substance abuse, medication use, infection, and exogenous stress. In the current review, we summarize environmental risk factors reported thus far in clinical and experimental studies relating to the programming of kidney disease, and systematize the knowledge on common mechanisms underlying renal programming. The aim of this review is to discuss the primary and secondary prevention actions for enhancing kidney health from pregnancy to age 2. The final task is to address the potential interventions to target renal programming through updating animal studies. Together, we can enhance the future of global kidney health in the first 1000 days of life.

Overlap of vitamin A and vitamin D target genes with CAKUT-related processes

Congenital Anomalies of the Kidney and Urinary Tract (CAKUT) are a group of abnormalities affecting the kidneys and their outflow tracts. CAKUT patients display a large clinical variability as well as a complex aetiology. Only 5% to 20% of the cases have a monogenic origin. It is thereby suspected that interactions of both genetic and environmental factors contribute to the disease. Vitamins are among the environmental factors that are considered for CAKUT aetiology. In this study, we aimed to investigate whether vitamin A or vitamin D could have a role in CAKUT aetiology. For this purpose we collected vitamin A and vitamin D target genes and computed their overlap with CAKUT-related gene sets. We observed limited overlap between vitamin D targets and CAKUT-related gene sets. We however observed that vitamin A target genes significantly overlap with multiple CAKUT-related gene sets, including CAKUT causal and differentially expressed genes, and genes involved in renal system development. Overall, these results indicate that an excess or deficiency of vitamin A might be relevant to a broad range of urogenital abnormalities.

Programming of Renal Development and Chronic Disease in Adult Life

Chronic kidney disease (CKD) can have an insidious onset because there is a gradual decline in nephron number throughout life. There may be no overt symptoms of renal dysfunction until about two thirds or more of the nephrons have been destroyed and glomerular filtration rate (GFR) falls to below 25% of normal (often in mid-late life) (Martinez-Maldonaldo et al., 1992). Once End Stage Renal Disease (ESRD) has been reached, survival depends on renal replacement therapy (RRT). CKD causes hypertension and cardiovascular disease; and hypertension causes CKD. Albuminuria is also a risk factor for cardiovascular disease. The age of onset of CKD is partly determined during fetal life. This review describes the mechanisms underlying the development of CKD in adult life that results from abnormal renal development caused by an adverse intrauterine environment. The basis of this form of CKD is thought to be mainly due to a reduction in the number of nephrons formed in utero which impacts on the age dependent decline in glomerular function. Factors that affect the risk of reduced nephron formation during intrauterine life are discussed and include maternal nutrition (malnutrition and obesity, micronutrients), smoking and alcohol, use of drugs that block the maternal renin-angiotensin system, glucocorticoid excess and maternal renal dysfunction and prematurity. Since CKD, hypertension and cardiovascular disease add to the disease burden in the community we recommend that kidney size at birth should be recorded using ultrasound and those individuals who are born premature or who have small kidneys at this time should be monitored regularly by determining GFR and albumin:creatinine clearance ratio. Furthermore, public health measures aimed at limiting the prevalence of obesity and diabetes mellitus as well as providing advice on limiting the amount of protein ingested during a single meal, because they are all associated with increased glomerular hyperfiltration and subsequent glomerulosclerosis would be beneficial.

Vitamin A deficiency increases the oleic acid (C18:1) levels in the kidney of high fructose diet-fed rats

Background & objectives

Stearoyl-CoA desaturase 1 (SCD1) is a key lipogenic enzyme responsible for endogenous synthesis of monounsaturated fatty acids (MUFA) and plays a key role in various pathophysiology, including fatty liver diseases. In this experimental study the impact of vitamin A deficiency was assessed on SCD1 regulation in relation to kidney biology, under high fructose (HFr) diet-fed condition in rats.

Methods

Forty male weanling (21 day old) Wistar rats were divided into four groups control, vitamin A-deficient (VAD), HFr, VAD with HFr consisting of eight rats each, except 16 for the VAD group. The groups received one of the following diets: control, VAD, HFr and VAD with HFr for 16 wk, except half of the VAD diet-fed rats were shifted to HFr diet, after eight week period.

Results

Feeding of VAD diet (alone or with HFr) significantly reduced the kidney retinol (0.51, 0.44 μg/g vs. 2.1 μg/g; P < 0.05), while increased oleic (C18:1) and total MUFA levels (23.3, 22.2% and 27.3, 25.4% respectively vs. 14.7 and 16.6%; P < 0.05) without affecting the SCD1, both at protein and mRNA levels, when compared with HFr. Comparable, immunohistological staining for SCD1 was observed in the distal convoluted tubules. Despite an increase in MUFA, morphology, triglyceride content and markers of kidney function were not affected by VAD diet feeding.

Interpretation & conclusions

Feeding of VAD diet either alone or under HFr condition increased the kidney oleic acid (C18:1) levels and thus total MUFA, which corroborated with elevated SCD1 activity index, without affecting its expression status. However, these changes did not alter the kidney morphology and function. Thus, nutrient-gene regulation in kidney biology seems to be divergent.

Genetic and Developmental Factors in Chronic Kidney Disease Hotspots

Chronic kidney disease increasingly is being recognized as an important global public health problem. Interindividual susceptibility to kidney disease is high and likely is dependent on risk modulation through genetics, fetal and early childhood development, environmental circumstances, and comorbidities. Traditionally, the chronic kidney disease burden has been ascribed largely to hypertension and diabetes. Increasingly, evidence is accumulating that nontraditional risk factors may predominate in some regions and populations, contributing to epidemics of kidney disease. Such nontraditional risk factors include environmental exposures, traditional medicines, fetal and maternal factors, infections, kidney stones, and acute kidney injury. Genetic factors may predispose patients to chronic kidney disease in some populations. Chronic kidney disease of unknown origin has its epicenters in Central America and South Asia. Such clustering of CKD may represent either genetic or environmentally driven kidney disease, or combinations of both. Developmental conditions impacting kidney development often are related to poverty and structural factors that persist throughout life. In this article, we explore the possibilities that genetic and developmental factors may be important contributors to the epidemics in these regions and suggest that optimization of factors impacting kidney development hold promise to reduce the risk of kidney disease in future generations.

A Primer on Congenital Anomalies of the Kidneys and Urinary Tracts (CAKUT)

Congenital anomalies of the kidneys and urinary tracts (CAKUT) are disorders caused by defects in the development of the kidneys and their outflow tracts. The formation of the kidneys begins at week 3 and nephrogenesis continues until week 36, therefore, the kidneys and outflow tracts are susceptible to environmental risk factors that perturb development throughout gestation. Many genes have been implicated in kidney and outflow tract development, and mutations have been identified in patients with CAKUT. In severe cases of CAKUT, when the kidneys do not form, the fetus will not survive. However, in less severe cases, the baby can survive with combined kidney and outflow tract defects or they may only be identified in adulthood. In this review, we will cover the clinical presentation of CAKUT, its epidemiology, and its long-term outcomes. We will then discuss risk factors for CAKUT, including genetic and environmental contributions. Although severe CAKUT is rare, low nephron number is a much more common disorder with its effect on kidney function increasingly apparent as a person ages. Low nephron number appears to arise by the same mechanisms as CAKUT, but it differs in terms of the magnitude of the insult and the timing of when it occurs during gestation. By understanding the causes of CAKUT and low nephron number, we can begin to identify preventive treatments and establish clinical guidelines for how these patients should be followed.

Clinical consequences of developmental programming of low nephron number

Nephron number in humans varies up to 13-fold, likely reflecting the impact of multiple factors on kidney development, including inherited body size and ethnicity, as well as maternal health and nutrition, fetal exposure to gestational diabetes or preeclampsia and other environmental factors, which may potentially be modifiable. Such conditions predispose to low or high offspring birth weight, growth restriction or preterm birth, which have all been associated with increased risks of higher blood pressures and/or kidney dysfunction in later life. Low birth weight, preterm birth, and intrauterine growth restriction are associated with reduced nephron numbers. Humans with hypertension and chronic kidney disease tend to have fewer nephrons than their counterparts with normal blood pressures or kidney function. A developmentally programmed reduction in nephron number therefore enhances an individual's susceptibility to hypertension and kidney disease in later life. A low nephron number at birth may not lead to kidney dysfunction alone except when severe, but in the face of superimposed acute or chronic kidney injury, a kidney endowed with fewer nephrons may be less able to adapt, and overt kidney disease may develop. Given that millions of babies are born either too small, too big or too soon each year, the population impact of altered renal programming is likely to be significant. Many gestational exposures are modifiable, therefore urgent attention is required to implement public health measures to optimize maternal, fetal, and child health, to prevent or mitigate the consequences of developmental programming, to improve the health future generations.

The Relationship between Maternal Nutrition during Pregnancy and Offspring Kidney Structure and Function in Humans: A Systematic Review

The intrauterine environment is critical for fetal growth and organ development. Evidence from animal models indicates that the developing kidney is vulnerable to suboptimal maternal nutrition and changes in health status. However, evidence from human studies are yet to be synthesised. Therefore, the aim of the current study was to systematically review current research on the relationship between maternal nutrition during pregnancy and offspring kidney structure and function in humans. A search of five databases identified 9501 articles, of which three experimental and seven observational studies met the inclusion criteria. Nutrients reviewed to date included vitamin A (n = 3), folate and vitamin B12 (n = 2), iron (n = 1), vitamin D (n = 1), total energy (n = 2) and protein (n = 1). Seven studies were assessed as being of "positive" and three of "neutral" quality. A variety of populations were studied, with limited studies investigating maternal nutrition during pregnancy, while measurements of offspring kidney outcomes were diverse across studies. There was a lack of consistency in the timing of follow-up for offspring kidney structure and/or function assessments, thus limiting comparability between studies. Deficiencies in maternal folate, vitamin A, and total energy during pregnancy were associated with detrimental impacts on kidney structure and function, measured by kidney volume, proteinuria, eGFR_cystC and mean creatinine clearance in the offspring. Additional experimental and longitudinal prospective studies are warranted to confirm this relationship, especially in Indigenous populations where the risk of renal disease is greater.

Renal development in the fetus and premature infant

Congenital abnormalities of the kidney and urinary tract (CAKUT) are one of the leading congenital defects to be identified on prenatal ultrasound. CAKUT represent a broad spectrum of abnormalities, from transient hydronephrosis to severe bilateral renal agenesis. CAKUT are a major contributor to chronic and end stage kidney disease (CKD/ESKD) in children. Prenatal imaging is useful to identify CAKUT, but will not detect all defects. Both genetic abnormalities and the fetal environment contribute to CAKUT. Monogenic gene mutations identified in human CAKUT have advanced our understanding of molecular mechanisms of renal development. Low nephron number and solitary kidneys are associated with increased risk of adult onset CKD and ESKD. Premature and low birth weight infants represent a high risk population for low nephron number. Additional research is needed to identify biomarkers and appropriate follow-up of premature and low birth weight infants into adulthood.

The Impact of Kidney Development on the Life Course: A Consensus Document for Action

Hypertension and chronic kidney disease (CKD) have a significant impact on global morbidity and mortality. The Low Birth Weight and Nephron Number Working Group has prepared a consensus document aimed to address the relatively neglected issue for the developmental programming of hypertension and CKD. It emerged from a workshop held on April 2, 2016, including eminent internationally recognized experts in the field of obstetrics, neonatology, and nephrology. Through multidisciplinary engagement, the goal of the workshop was to highlight the association between fetal and childhood development and an increased risk of adult diseases, focusing on hypertension and CKD, and to suggest possible practical solutions for the future. The recommendations for action of the consensus workshop are the results of combined clinical experience, shared research expertise, and a review of the literature. They highlight the need to act early to prevent CKD and other related noncommunicable diseases later in life by reducing low birth weight, small for gestational age, prematurity, and low nephron numbers at birth through coordinated interventions. Meeting the current unmet needs would help to define the most cost-effective strategies and to optimize interventions to limit or interrupt the developmental programming cycle of CKD later in life, especially in the poorest part of the world.

Umbilical artery histomorphometry: a link between the intrauterine environment and kidney development

Prematurity is a risk factor for hypertension, vascular stiffness, nephron deficit and adult onset cardiorenal disease. The vascular tree and kidneys share morphogenic drivers that promote maturation in utero before 36 weeks of gestation. Vascular elastin accrual terminates after birth leaving collagen to promote vascular stiffness. Our objective was to determine if the histomorphometry of the umbilical artery, an extension of the aorta, parallels nephron mass across gestational age groups. From a cohort of 54 newborns, 32 umbilical cord specimens were adequate for evaluation. The umbilical cord was sectioned, stained with trichrome, and digitalized. Muscular and collagenous areas of the umbilical artery were measured in pixels using the Image J 1.48q software. Total kidney volume was measured by ultrasound and factored by body surface area (TKV/BSA). The umbilical artery total area was significantly greater in term v. preterm infants (9.3±1.3 v. 7.0±2.0 mm2; P<0.05) and increased with gestational age; while the percent muscular and collagen areas were independent of gestational age (R 2=0.04; P=ns). Percent muscular area correlated positively with TKV/BSA (r=0.53; P=0.002); while an increase in collagen correlated inversely with kidney mass (r=-0.53; P=0.002). In conclusion, an enhanced % muscular area and presumed vascular elasticity was associated with increased renal mass in all infants. Umbilical artery histomorphometry provides a link between the intrauterine environment, vascular and kidney development.

Are low birth weight neonates at risk for suboptimal renal growth and function during infancy?

Background

To assess the renal growth and function of neonates during infancy in relation to birth weight and gestational age.

Methods

A longitudinal study was conducted at a tertiary hospital in South India from June 2010 to August 2014. Low birth weight neonates (LBW) were further sub-classified based on gestational age and compared with normal birth weight (NBW) full term neonates at birth, 6 months and 18-24months of age. The renal volume was measured by ultrasound and renal function by Cystatin C- derived glomerular filtration rate (CysGFR) at the three time points during the dynamic phase of renal maturation in infancy.

Results

We recruited 100 LBW and 66 NBW term neonates. Thirty five percent of the LBW neonates were SGA. Among the AGA neonates, 39 % were LBW neonates. The mean height and weight of the LBW neonates were significantly lower compared to NBW neonates throughout infancy. The increment in kidney volume was in accordance with the change in body size, being lower in LBW compared to NBW infants. The combined kidney volume was significantly lower in LBW and SGA neonates across all three time points (p < 0.001). CysGFR in the LBW and SGA infants, despite having low kidney volumes, were comparable to the GFRs of NBW and AGA neonates at the end of infancy.

Conclusion

This study highlights the fact that both birth weight and gestational age influence kidney growth and function in infancy. At the end of infancy, despite a significant difference in kidney volumes and age at last follow up, the glomerular filtration rate was comparable between LBW and NBW infants. Though not statistically significant, there was a trend towards higher urine microalbumin in LBW compared to NBW in infancy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-016-0314-7) contains supplementary material, which is available to authorized users.

Chronic kidney disease hotspots in developing countries in South Asia

In many developing countries in the South Asian region, screening for chronic diseases in the community has shown a widely varying prevalence. However, certain geographical regions have shown a high prevalence of chronic kidney disease (CKD) of unknown etiology. This predominantly affects the young and middle-aged population with a lower socioeconomic status. Here, we describe the hotspots of CKD of undiagnosed etiology in South Asian countries including the North, Central and Eastern provinces of Sri Lanka and the coastal region of the state of Andhra Pradesh in India. Screening of these populations has revealed cases of CKD in various stages. Race has also been shown to be a factor, with a much lower prevalence of CKD in whites compared to Asians, which could be related to the known influence of ethnicity on CKD development as well as environmental factors. The difference between developed and developing nations is most stark in the realm of healthcare, which translates into CKD hotspots in many regions of South Asian countries. Additionally, the burden of CKD stage G5 remains unknown due to the lack of registry reports, poor access to healthcare and lack of an organized chronic disease management program. The population receiving various forms of renal replacement therapy has dramatically increased in the last decade due to better access to point of care, despite the disproportionate increase in nephrology manpower. In this article we will discuss the nephrology care provided in various countries in South Asia, including India, Bangladesh, Pakistan, Nepal, Bhutan, Sri Lanka and Afghanistan.

Birth weight, malnutrition and kidney-associated outcomes--a global concern

An adverse intrauterine environment is associated with an increased risk of elevated blood pressure and kidney disease in later life. Many studies have focused on low birth weight, prematurity and growth restriction as surrogate markers of an adverse intrauterine environment; however, high birth weight, exposure to maternal diabetes and rapid growth during early childhood are also emerging as developmental risk factors for chronic diseases. Altered programming of nephron number is an important link between exposure to developmental stressors and subsequent risk of hypertension and kidney disease. Maternal, fetal, and childhood nutrition are crucial contributors to these programming effects. Resource-poor countries experience the sequential burdens of fetal and childhood undernutrition and subsequent overnutrition, which synergistically act to augment the effects of developmental programming; this observation might explain in part the disproportionate burden of chronic disease in these regions. Numerous nutritional interventions have been effective in reducing the short-term risk of low birth weight and prematurity. Understanding the potential long-term benefits of such interventions is crucial to inform policy decisions to interrupt the developmental programming cycle and stem the growing epidemics of hypertension and kidney disease worldwide.

Renal branching morphogenesis: morphogenetic and signaling mechanisms

The human kidney is composed of an arborized network of collecting ducts, calyces and urinary pelvis that facilitate urine excretion and regulate urine composition. The renal collecting system is formed in utero, completed by the 34th week of gestation in humans, and dictates final nephron complement. The renal collecting system arises from the ureteric bud, a derivative of the intermediate-mesoderm derived nephric duct that responds to inductive signals from adjacent tissues via a process termed ureteric induction. The ureteric bud subsequently undergoes a series of iterative branching and remodeling events in a process called renal branching morphogenesis. Altered signaling that disrupts patterning of the nephric duct, ureteric induction, or renal branching morphogenesis leads to varied malformations of the renal collecting system collectively known as congenital anomalies of the kidney and urinary tract (CAKUT) and is the most frequently detected congenital renal aberration in infants. Here, we describe critical morphogenetic and cellular events that govern nephric duct specification, ureteric bud induction, renal branching morphogenesis, and cessation of renal branching morphogenesis. We also highlight salient molecular signaling pathways that govern these processes, and the investigative techniques used to interrogate them.

Outcome following prenatal diagnosis of severe bilateral renal hypoplasia

OBJECTIVE

The aim of this research was to evaluate the outcome and prognostic value of fetal serum β2-microglobulin in case of prenatal diagnosis of severe bilateral renal hypoplasia.

METHODS

Cases of hypoplastic kidneys were detected on ultrasound and referred to our laboratory for determination of fetal blood β2-microglobulin, over a 12-year period. Prenatal prognostic assessment was based upon amniotic fluid volume and fetal serum β2-microglobulin (cut-off: 5 mg/L). Outcome measures were postnatal renal function or renal pathological features when termination of pregnancy (TOP) and genetic studies were performed.

RESULTS

A total of 34 cases were identified; 13 (38%) were liveborn and 21 (62%) underwent TOP. Renal hypoplasia was confirmed postnatally in all cases. Oligohydramnios/anhydramnios was observed in 30/34 (88%) cases. Associated genetic or anatomical anomalies were found in 8/34 (24%) cases. Renal function of liveborn infants was normal in 4/13 cases. Renal lesions were observed in all TOPs (21/21 cases). Overall, 30/34 (88.2%) cases had a poor outcome. β2-microglobulin accurately predicts poor renal outcome in 27/31 (87.1%) cases. β2-microglobulin was not interpretable in three cases due to amniotic fluid contamination. The prognostic value of β2-microglobulin was similar to that of amniotic fluid volume assessment.

CONCLUSION

Hypoplastic kidneys complicated by oligohydramnios/anhydramnios are associated with poor outcome. Fetal serum β2-microglobulin and oligohydramnios both predicted poor outcome.

Effect of fetal and child health on kidney development and long-term risk of hypertension and kidney disease

Developmental programming of non-communicable diseases is now an established paradigm. With respect to hypertension and chronic kidney disease, adverse events experienced in utero can affect development of the fetal kidney and reduce final nephron number. Low birthweight and prematurity are the most consistent clinical surrogates for a low nephron number and are associated with increased risk of hypertension, proteinuria, and kidney disease in later life. Rapid weight gain in childhood or adolescence further compounds these risks. Low birthweight, prematurity, and rapid childhood weight gain should alert clinicians to an individual's lifelong risk of hypertension and kidney disease, prompting education to minimise additional risk factors and ensuring follow-up. Birthweight and prematurity are affected substantially by maternal nutrition and health during pregnancy. Optimisation of maternal health and early childhood nutrition could, therefore, attenuate this programming cycle and reduce the global burden of hypertension and kidney disease in the future.

Short-term gestation, long-term risk: prematurity and chronic kidney disease

Thanks to remarkable advances in neonatal intensive care, infants who once had little chance for survival can now enter adulthood. Yet the consequences of premature birth or low birth weight (LBW) on nephrogenesis, final nephron number, and long-term kidney function are unclear. This review focuses on the theory, experimental evidence, and observational data that suggest an increased risk of chronic kidney disease (CKD) for infants born prematurely. Many premature and LBW infants begin life with an incomplete complement of immature nephrons. They are then exposed to a variety of external stressors that can hinder ongoing kidney development or cause additional nephron loss such as hemodynamic alterations, nephrotoxic medications, infections, and suboptimal nutrition. Acute kidney injury, in particular, may be a significant risk factor for the development of CKD. According to Brenner's hypothesis, patients with decreased nephron number develop hyperfiltration that results in sodium retention, hypertension, nephron loss, and CKD due to secondary focal segmental glomerulosclerosis. Because the risk of CKD in premature and LBW infants has not been accurately determined, there are no evidence-based recommendations for screening or management. Yet with the first generation of infants from the surfactant era only now reaching adulthood, it is possible that there is already an unrecognized epidemic of CKD. We suggest individualized, risk-based assessments of premature and LBW infants due to the increased risk of CKD and call for additional research into the long-term risk for CKD these infants face.

Evaluation of High Resolution Melting analysis as an alternate tool to screen for risk alleles associated with small kidneys in Indian newborns

BACKGROUND

Single nucleotide polymorphisms (SNPs) are the most common forms of sequence variations in the human genome. They contribute to the human phenotypic spectrum and are associated with variations in response to pathogens, drugs and vaccines. Recently, SNPs in three human genes involved in kidney development (RET, PAX2 and ALDH1A2) have been reported to be associated with variation in renal size and function. These known SNPs could potentially be used in the clinic as markers for identifying babies who may have smaller kidneys and permit close follow up for early detection of hypertension and acquired renal dysfunction. The aim of this study was to evaluate the use of High Resolution Melting technique (HRM) as a tool for detecting the known SNPs in these three genes in comparison to sequencing which is the gold standard.

METHODS

High resolution melting analysis was performed on 75 DNA samples that were previously sequenced for the known polymorphisms in RET (rs1800860), PAX2 (rs11190688) and ALDH1A2 (rs7169289) genes. The SNPs were G > A transitions in RET and PAX2 and A > G in ALDH1A2 gene. A blinded assessment was performed on these samples for evaluation of the HRM technique as compared to sequencing.

RESULTS

Each variant had a unique melt curve profile that was reproducible. The shift in melting temperature (Tm) allowed visual discrimination between the homozygous alleles (major and minor) in all three genes. The shape of the melting curve as compared to the major allele homozygous curve allowed the identification of the heterozygotes in each of the three SNPs. For validation, HRM was performed on 25 samples for each of the three SNPs. The results were compared with the sequencing results and 100% correct identification of the samples was obtained for RET, PAX2, and ALDA1H2 gene.

CONCLUSION

High Resolution Melting analysis is a simple, rapid and cost effective technique that could be used in a large population to identify babies with the risk alleles. These high risk children could be followed up for early detection of hypertension and acquired renal dysfunction.

Glomerular number and size variability and risk for kidney disease

PURPOSE OF REVIEW

This review discusses current understandings of variability in glomerular number and size, and the implications for renal health.

RECENT FINDINGS

The quantitative microanatomy of the normal human kidney varies widely. Of greatest significance, total nephron number varies at least 13-fold, and several genes and environmental factors that regulate human nephron endowment have been identified. Full or partial deletion of more than 25 genes in mice has been shown to result in renal hypoplasia and, when measured, reduced nephron endowment. Many more will likely be identified. As would be expected, some gene abnormalities increase nephron endowment above that found in control mice. Glomerular volume also varies widely, both between and within kidneys, and increased heterogeneity of glomerular volume within kidneys is associated with risk factors for kidney disease, including birth weight, age, race, body size and hypertension.

SUMMARY

Data from several human populations indicate that the quantitative microanatomy of the human kidney varies considerably: total glomerular number varies at least 13-fold, mean glomerular volume varies up to seven-fold and the volumes of individual glomeruli within single kidneys can vary as much as eight-fold. Human glomerular number, size and size distribution are being found to correlate with risk factors for kidney disease. The genetic and fetal environmental regulators of nephrogenesis, and thereby nephron endowment, are being rapidly identified and will provide the bases for future clinical interventions. In contrast, the molecular regulation of glomerular size remains unclear.

Vitamin A deficiency results in dysregulation of lipid efflux pathway in rat kidney

The mechanisms of action of vitamin A deficiency (VAD) on lipid metabolism in the rat kidney were investigated in adult female rats and their offspring. The rats were randomized into three groups: (1) control, in which the mother and offspring received a normal diet (4000 retinol IU/kg diet) for 8 weeks; (2) VAD group, in which the mothers and offspring received a VAD diet (400 retinol IU/kg diet) for 8 weeks; (3) vitamin A-refed group, in which a group of pups on a VAD diet for 8 weeks received a complete diet (6500 retinol IU/kg diet) for 15 days. The lipid metabolism of the offsprings' kidneys and its relation to the expression of apolipoprotein B100 (Apo-B100), liver X receptor alpha (LXRalpha), and retinoid X receptor-alpha/beta (RXRalpha/beta) mRNA was analyzed. VAD was found to alter renal lipid metabolism and its immune environment due to the expression of Apo-B100. Compared with the control, VAD rats had significantly higher levels of transforming growth factor-beta 1 and lower levels of ABCA1, a key gene involved in cholesterol efflux and tissue lipid homeostasis. The expression of LXRalpha and RXRalpha/beta mRNA also decreased in the VAD rat kidney. Vitamin A refeeding reversed all of the changes. Lipid metabolism involved in renal reverse cholesterol transport may be mediated by decreasing the signaling through the ABCA1 cholesterol efflux pathway, which is significantly modified in kidneys of vitamin A-deficient rats.

Perinatal nutrient restriction reduces nephron endowment increasing renal morbidity in adulthood: a review

Perinatal malnutrition has been included among the causes of renal disease in adulthood. Here, we consider the relationships between early supply of specific nutrients (such as protein, fat, vitamins and electrolytes) and renal endowment. Prenatal and postnatal nutrition mismatch is also discussed. In addition, this article presents the role of nutrition of both mothers and pre-term infants on nephron endowment, with final practical considerations.

A human ALDH1A2 gene variant is associated with increased newborn kidney size and serum retinoic acid

Nephron number varies widely between 0.3 and 1.3 million per kidney in humans. During fetal life, the rate of nephrogenesis is influenced by local retinoic acid (RA) level such that even moderate maternal vitamin A deficiency limits the final nephron number in rodents. Inactivation of genes in the RA pathway causes renal agenesis in mice; however, the impact of retinoids on human kidney development is unknown. To resolve this, we tested for associations between variants of genes involved in RA metabolism (ALDH1A2, CYP26A1, and CYP26B1) and kidney size among normal newborns. Homozygosity for a common (1 in 5) variant, rs7169289(G), within an Sp1 transcription factor motif of the ALDH1A2 gene, showed a significant 22% increase in newborn kidney volume when adjusted for body surface area. Infants bearing this allele had higher umbilical cord blood RA levels compared to those with homozygous wild-type ALDH1A2 rs7169289(A) alleles. Furthermore, the effect of the rs7169289(G) variant was evident in subgroups with or without a previously reported hypomorphic RET 1476(A) proto-oncogene allele that is critical in determining final nephron number. As maternal vitamin A deficiency is widespread in developing countries and may compromise availability of retinol for fetal RA synthesis, our study suggests that the ALDH1A2 rs7169289(G) variant might be protective for such individuals.

Maternal micronutrient deficiency, fetal development, and the risk of chronic disease

Early life nutritional exposures, combined with changes in lifestyle in adult life, can result in increased risk of chronic diseases. Although much of the focus on the developmental origins of disease has been on birth size and growth in postnatal life and the availability of energy and protein during these critical developmental periods, micronutrient deficiencies may also play an important role in fetal growth and development. Micronutrient status in fetal and early life may alter metabolism, vasculature, and organ growth and function, leading to increased risk of cardiometabolic disorders, adiposity, altered kidney function, and, ultimately, to type 2 diabetes and cardiovascular diseases. This review elucidates pathways through which micronutrient deficiencies lead to developmental impairment and describes the research to date on the evidence that micronutrient deficiencies in utero influence the development of chronic disease risk. Animal studies, observational human studies examining maternal diet or micronutrient status, and limited data from intervention studies are reviewed. Where data are lacking, plausible mechanisms and pathways of action have been derived from the existing animal and in vitro models. This review fills a critical gap in the literature related to the seminal role of micronutrients in early life and extends the discussion on the developmental origins of health and disease beyond birth size and energy and protein deficiency.

Potential roles of high salt intake and maternal malnutrition in the development of hypertension in disadvantaged populations

1. It has been argued that all major risk factors for cardiovascular disease have been identified. Yet, epidemiological studies undertaken to identify risk factors have largely focused on populations in developed nations or on the urban or relatively affluent rural populations of developing countries. Poor rural populations are seldom studied. 2. Somewhat different risk factors may operate in poor rural populations. Evidence for this is provided by the finding that, in disadvantaged rural India, the prevalence of hypertension is greater than would be expected based on established risk factors in these populations. One risk factor to be considered is a poor intrauterine environment. 3. In animals, maternal macro- and micronutrient malnutrition can lead to reduced nephron endowment. Nephron deficiency, in turn, can render blood pressure salt sensitive. The combination of nephron deficiency and excessive salt intake will predispose to hypertension. 4. Human malnutrition may have similar effects, particularly in regions of the world where malnutrition is endemic and where women are disadvantaged by existing social practices. 5. Moreover, high salt intake is endemic in many parts of Asia, including India. Therefore, we propose that maternal malnutrition (leading to reduced nephron endowment), when combined with excessive salt intake postnatally, will account, at least in part, for the unexpectedly high prevalence of hypertension in disadvantaged rural communities in India and elsewhere.

A common RET variant is associated with reduced newborn kidney size and function

Congenital nephron number varies five-fold among normal humans, and individuals at the lower end of this range may have an increased lifetime risk for essential hypertension or renal insufficiency; however, the mechanisms that determine nephron number are unknown. This study tested the hypothesis that common hypomorphic variants of the RET gene, which encodes a tyrosine kinase receptor critical for renal branching morphogenesis, might account for subtle renal hypoplasia in some normal newborns. A common single-nucleotide polymorphism (rs1800860 G/A) was identified within an exonic splicing enhancer in exon 7. The adenosine variant at mRNA position 1476 reduced affinity for spliceosome proteins, enhanced the likelihood of aberrant mRNA splicing, and diminished the level of functional transcript in human cells. In vivo, normal white newborns with an rs1800860(1476A) allele had kidney volumes 10% smaller and cord blood cystatin C levels 9% higher than those with the rs1800860(1476G) allele. These findings suggest that the RET(1476A) allele, in combination with other common polymorphic developmental genes, may account for subtle renal hypoplasia in a significant proportion of the white population. Whether this gene variant affects clinical outcomes requires further study.

Role of vitamin A in determining nephron mass and possible relationship to hypertension

Vitamin A (retinol) and its analogs (retinoids) are important regulators of cell proliferation, differentiation, immune function, and apoptosis. The kidneys are target organs for vitamin A action. Retinoic acid (RA), a vitamin A metabolite, is involved in embryonic kidney patterning through the control of receptor tyrosine kinase expression, which modulates ureteric bud branching morphogenesis. Vitamin A status of the mother profoundly affects kidney organogenesis of the newborn. In rodents, mild vitamin A deficiency results in a 20% reduction of nephron number. In adult humans, nephron number varies between 0.3 and 1.3 million per kidney, which is accepted as normal. However, recent studies indicate that humans at the low end of nephron number are predisposed to primary hypertension. Because RA regulates nephron mass, its optimal availability during nephrogenesis is critical. RA levels in the embryo are affected by several factors, such as maternal vitamin A nutrition and disturbances in retinol metabolism. Maternal vitamin A deficiency during pregnancy is widespread in developing countries and segments of these populations may be exposed to low vitamin A during fetal life when nephron number is determined. Infants are likely to be born with suboptimal nephrons and may develop primary hypertension later in life. Although maternal vitamin A deficiency is not common in developed countries, congenital nephron number nevertheless varies widely, indicating low fetal RA levels due to common variants of the enzymes that convert retinol to RA. These infants might require heightened surveillance for hypertension later in life.

A common variant of the PAX2 gene is associated with reduced newborn kidney size

Congenital nephron number ranges widely in the human population. Suboptimal nephron number may be associated with increased risk for essential hypertension and susceptibility to renal injury, but the factors that set nephron number during kidney development are unknown. In renal-coloboma syndrome, renal hypoplasia and reduced nephron number are due to heterozygous mutations of the PAX2 gene. This study tested for an association between a common haplotype of the PAX2 gene and subtle renal hypoplasia in normal newborns. A PAX2 haplotype was identified to occur in 18.5% of the newborn cohort, which was significantly associated with a 10% reduction in newborn kidney volume adjusted for body surface area. This haplotype was also associated with reduced allele-specific PAX2 mRNA level in a human renal cell carcinoma cell line. Subtle renal hypoplasia in normal newborns may be partially due to a common variant of the PAX2 gene that reduces mRNA expression during kidney development.