Genotype-phenotype correlations in fetuses and neonates with autosomal recessive polycystic kidney disease

Congenital anomalies of the kidney and urinary tract: a genetic disorder?

Congenital anomalies of the kidney and urinary tract (CAKUTs) occur in 3–6 per 1000 live births, account for the most cases of pediatric end-stage kidney disease (ESKD), and predispose an individual to hypertension and cardiovascular disease throughout life. Although CAKUTs are a part of many known syndromes, only few single-candidate causative genes have been implicated so far in nonsyndromic cases of human CAKUT. Evidence from mouse models supports the hypothesis that non-syndromic human CAKUT may be caused by single-gene defects. Because increasing numbers of children with CAKUT are surviving to adulthood, better understanding of the molecular pathogenesis of CAKUT, development of new strategies aiming at prevention of CAKUT, preservation of renal function, and avoidance of associated cardiovascular morbidity are needed. In this paper, we will focus on the knowledge derived from the study of syndromic and non-syndromic forms of CAKUT in humans and mouse mutants to discuss the role of genetic, epigenetic, and in utero environmental factors in the pathogenesis of non-syndromic forms of CAKUT in children with particular emphasis on the genetic contributions to CAKUT.

Caroli's Disease: Current Knowledge of Its Biliary Pathogenesis Obtained from an Orthologous Rat Model

Caroli's disease belongs to a group of hepatic fibropolycystic diseases and is a hepatic manifestation of autosomal recessive polycystic kidney disease (ARPKD). It is a congenital disorder characterized by segmental saccular dilatations of the large intrahepatic bile duct and is frequently associated with congenital hepatic fibrosis (CHF). The most viable theory explaining its pathogenesis suggests that it is related to ductal plate malformation. The development of the polycystic kidney (PCK) rat, an orthologous rodent model of Caroli's disease with CHF as well as ARPKD, has allowed the molecular pathogenesis of the disease and the therapeutic options for its treatment to be examined. The relevance of the findings of studies using PCK rats and/or the cholangiocyte cell line derived from them to the pathogenesis of human Caroli's disease is currently being analyzed. Fibrocystin/polyductin, the gene product responsible for ARPKD, is normally localized to primary cilia, and defects in the fibrocystin from primary cilia are observed in PCK cholangiocytes. Ciliopathies involving PCK cholangiocytes (cholangiociliopathies) appear to be associated with decreased intracellular calcium levels and increased cAMP concentrations, causing cholangiocyte hyperproliferation, abnormal cell matrix interactions, and altered fluid secretion, which ultimately result in bile duct dilatation. This article reviews the current knowledge about the pathogenesis of Caroli's disease with CHF, particularly focusing on studies of the mechanism responsible for the biliary dysgenesis observed in PCK rats.

A classification of ductal plate malformations based on distinct pathogenic mechanisms of biliary dysmorphogenesis

Ductal plate malformations (DPMs) are developmental anomalies considered to result from lack of ductal plate remodeling during bile duct morphogenesis. In mice, bile duct development is initiated by the formation of primitive ductal structures lined by two cell types, namely ductal plate cells and hepatoblasts. During ductal plate remodeling, the primitive ductal structures mature to ducts as a result from differentiation of the ductal plate cells and hepatoblasts to cholangiocytes. Here, we report this process is conserved in human fetal liver. These findings prompted us to evaluate how DPMs develop in three mouse models, namely mice with livers deficient in hepatocyte nuclear factor 6 (HNF6), HNF1β, or cystin-1 (cpk [congenital polycystic kidney] mice). Human liver from a patient with a HNF1B/TCF2 mutation, and from fetuses affected with autosomal recessive polycystic kidney disease (ARPKD) were also analyzed. Despite the epistatic relationship between HNF6, HNF1β, and cystin-1, the three mouse models displayed distinct morphogenic mechanisms of DPM. They all developed biliary cysts lined by cells with abnormal apicobasal polarity. However, the absence of HNF6 led to an early defect in ductal plate cell differentiation. In HNF1β-deficient liver, maturation of the primitive ductal structures was impaired. Normal differentiation and maturation but abnormal duct expansion was apparent in cpk mouse livers and in human fetal ARPKD.

CONCLUSION

DPM is the common endpoint of distinct defects initiated at distinct stages of bile duct morphogenesis. Our observations provide a new pathogenic classification of DPM.

Similar renal outcomes in children with ADPKD diagnosed by screening or presenting with symptoms

Autosomal dominant polycystic kidney disease (ADPKD) in children is sometimes considered to be a benign condition, with morbidity manifesting in adulthood. Therefore, diagnostic screening of children at risk is controversial. The aim of our study was to to compare the manifestations of ADPKD in children diagnosed by postnatal ultrasound (US) screening versus those presenting with symptoms. This was a retrospective chart review of children with ADPKD assessed in a single centre between 1987 and 2007. Age and reason for diagnosis were noted, and children were separated into two groups: (1) those diagnosed on the basis of family-based screening; (2) those presenting with a symptom. The two groups were compared for renal size, number of cysts, estimated glomerular filtration rate (eGFR), the presence of hypertension and microalbuminuria. In the 47 children with ADPKD (21 females) from 33 families who satisfied the enrollment criteria, mean (standard deviation) age at referral and last follow-up was 7.2 (4.4) and 12.9 (5.1) years, respectively, and the mean follow-up duration was 5.7 (3.6) years. Diagnosis was based on postnatal US screening in 31 children, whereas 16 were diagnosed after presenting with symptoms. The proportions of children with nephromegaly, hypertension, microalbuminuria and decreased eGFR, respectively, were similar in both groups. Based on these results, we conclude that renal-related morbidities, including hypertension and microalbuminia, do occur in children with ADPKD and at a similar frequency in those diagnosed after presenting with symptoms and those diagnosed upon postnatal screening. We suggest that at-risk children should have regular checks to detect hypertension. Moreover, affected children may benefit from novel therapies to minimise cystic disease progression.

Polycystic kidney disease: inheritance, pathophysiology, prognosis, and treatment

Both autosomal dominant and recessive polycystic kidney disease are conditions with severe associated morbidity and mortality. Recent advances in the understanding of the genetic and molecular pathogenesis of both ADPKD and ARPKD have resulted in new, targeted therapies designed to disrupt cell signaling pathways responsible for the abnormal cell proliferation, dedifferentiation, apoptosis, and fluid secretion characteristic of the disease. Herein we review the current understanding of the pathophysiology of these conditions, as well as the current treatments derived from our understanding of the mechanisms of these diseases.