Autosomal Recessive Polycystic Kidney Disease Cases Research Articles

The genetics of Autosomal Recessive Polycystic Kidney Disease (ARPKD).

ARPKD is a genetically inherited kidney disease that manifests by bilateral enlargement of cystic kidneys and liver fibrosis. It shows a range of severity, with 30% of individuals dying early on and the majority having good prognosis if they survive the first year of life. The reasons for this variability remain unclear. Two genes have been shown to cause ARPKD when mutated, PKHD1, mutations in which lead to most of ARPKD cases and DZIP1L, which is associated with moderate ARPKD. This mini review will explore the genetics of ARPKD and discuss potential genetic modifiers and phenocopies that could affect diagnosis.

Loss of Cilia Does Not Slow Liver Disease Progression in Mouse Models of Autosomal Recessive Polycystic Kidney Disease.

Autosomal dominant polycystic kidney disease (ADPKD) is a hereditary disorder characterized by abnormal cellular proliferation, cyst fluid accumulation, extracellular matrix remodeling, and fibrosis in the kidney and liver. ADPKD accounts for approximately 5% of the prevalent adult RRT (dialysis or transplantation) population, with most cases resulting from mutations in PKD1 or PKD2 , which encodes polycystin-1 (PC1) or polycystin-2 (PC2), respectively (1). In contrast, autosomal recessive polycystic kidney disease (ARPKD) is a rare and severe form of polycystic disease affecting the kidneys and biliary tract of children with an estimated incidence of 1 in 20,000 live births (2). ARPKD develops in utero and is diagnosed early in life, often prenatally. The clinical spectrum is widely variable, with approximately 20% of cases severely affected at birth, whereas the remainder are affected more as juveniles. Clinical findings in ARPKD include enlarged echogenic kidneys due to fusiform dilation of the collecting ducts and dilated bile ducts accompanied by congenital hepatic fibrosis resulting in portal hypertension (2). Mutations in PKHD1 are responsible for most typical cases of ARPKD (3,4). It encodes a heavily glycosylated approximately 450-kD single-pass transmembrane protein, fibrocystin (FPC), that localizes to the primary cilia, basal bodies, apical membrane, and exosome-like vesicles in kidney and liver epithelial cells (5⇓–7). The function of FPC is largely unknown, but it has been proposed to act as a ligand or cell surface coreceptor that undergoes Notch-like processing and plays a role in regulating mitotic spindle orientation (8⇓–10). Several rodent models for ARPKD have been reported with all but one targeting the 5′ region of the Pkhd1 gene. These models invariably exhibit biliary cysts accompanied by periportal fibrosis consistent with the human disease (5,11,12). The renal phenotype is mild in the rat model …

Clinical and genetic characteristics of autosomal recessive polycystic kidney disease in Oman

BackgroundThere is a high prevalence of rare genetic disorders in the Middle East, and their study provides unique clinical and genetic insights. Autosomal recessive polycystic kidney disease (ARPKD) is one of the leading causes of kidney and liver-associated morbidity and mortality in Oman. We describe the clinical and genetic profile of cohort of ARPKD patients.MethodsWe studied patients with a clinical diagnosis of ARPKD (n = 40) and their relatives (parents (n = 24) and unaffected siblings (n = 10)) from 32 apparently unrelated families, who were referred to the National Genetic Centre in Oman between January 2015 and December 2018. Genetic analysis of PKHD1 if not previously known was performed using targeted exon PCR of known disease alleles and Sanger sequencing.ResultsA clinical diagnosis of ARPKD was made prenatally in 8 patients, 21 were diagnosed during infancy (0–1 year), 9 during early childhood (2–8 years) and 2 at later ages (9–13 years). Clinical phenotypes included polycystic kidneys, hypertension, hepatic fibrosis and splenomegaly. Twenty-four patients had documented chronic kidney disease (median age 3 years). Twenty-four out of the 32 families had a family history suggesting an autosomal recessive pattern of inherited kidney disease, and there was known consanguinity in 21 families (66%). A molecular genetic diagnosis with biallelic PKHD1 mutations was known in 18 patients and newly identified in 20 other patients, totalling 38 patients from 30 different families. Two unrelated patients remained genetically unsolved. The different PKHD1 missense pathogenic variants were: c.107C > T, p.(Thr36Met); c.406A > G, p.(Thr136Ala); c.4870C > T, p.(Arg1624Trp) and c.9370C > T, p.(His3124Tyr) located in exons 3, 6, 32 and 58, respectively. The c.406A > G, p.(Thr136Ala) missense mutation was detected homozygously in one family and heterozygously with a c.107C > T, p.(Thr36Met) allele in 5 other families. Overall, the most commonly detected pathogenic allele was c.107C > T; (Thr36Met), which was seen in 24 families.ConclusionsMolecular genetic screening of PKHD1 in clinically suspected ARPKD cases produced a high diagnostic rate. The limited number of PKHD1 missense variants identified in ARPKD cases suggests these may be common founder alleles in the Omani population. Cost effective targeted PCR analysis of these specific alleles can be a useful diagnostic tool for future cases of suspected ARPKD in Oman.

SAT-436 CLINICAL AND GENETIC CHARACTERISTICS OF AUTOSOMAL RECESSIVE POLYCYSTIC KIDNEY DISEASE (ARPKD) PATIENTS FROM OMAN AND PKHD1 FOUNDER MUTATIONS

The Omani population has a high prevalence of rare genetic disorders, and their study provides unique clinical and genetic insights. Autosomal recessive polycystic kidney disease (ARPKD) is one of the leading causes of kidney and liver-associated morbidity and mortality in the country. We aimed to describe the clinical and genetic profile of ARPKD patients from Oman. A group of 75 patients and relatives (40 males and 35 females) from apparently 33 unrelated families, who were referred to the National Genetic Centre in Oman between January 2015 and December 2018, were studied. This included 41 patients with a clinical diagnosis of ARPKD, their parents (n=24) and siblings or relatives (n=10). Genetic analysis of PKHD1 was performed through next generation sequencing (NGS) and Sanger sequencing. A clinical diagnosis was made in 5 patients prenatally, 24 were diagnosed during the infancy period (0-1 year), nine during early childhood (2-8 years) and 3 at later ages (9-13 years). The main clinical features of patients included hypertension, hepatic fibrosis and splenomegaly. 25 patients had documented chronic renal failure at a median age of 3 years. 24 out of 33 families had a family history suggesting an autosomal recessive pattern of inheritance, and there was known consanguinity in 22 families (67%). A molecular genetic diagnosis of ARPKD with biallelic PKHD1 mutations was confirmed in 30 families (n= 38 patients), giving a detection rate of 91%. Three families remained genetically unsolved. In total, only four different PKHD1 missense pathogenic mutations were identified: c.107C>T; (Thr36Met), c.406A>G; (Thr136Ala), c.4870C>T; (Arg1624Trp) and c.9370C>T; (His3124Tyr) located in exons 3, 6, 32 and 58, respectively. The c.406A>G; (Thr136Ala) is a novel missense mutation that was detected homozygously in one family and heterozygously with c.107C>T; (Thr36Met) allele in 5 other families. Overall, the most commonly detected pathogenic allele was c.107C>T; (Thr36Met), which was seen in 24 families. All four PKHD1 mutations were detected in patients from all governorates of the country except, Musandam, Al Wusta and Dhofar. Molecular genetic screening of suspected ARPKD cases produces a highly yield of genetic diagnosis. The four PKHD1 missense mutations may suggest common founder alleles in Omani population and allow cost effective targeted PCR analysis of these specific alleles to be a useful diagnostic tool.

Comprehensive genetic testing in children with a clinical diagnosis of ARPKD identifies phenocopies.

Autosomal recessive polycystic kidney disease (ARPKD) is genetically one of the least heterogeneous ciliopathies, resulting primarily from mutations of PKHD1. Nevertheless, 13-20% of patients diagnosed with ARPKD are found not to carry PKHD1 mutations by sequencing. Here, we assess whether PKHD1 copy number variations or second locus mutations explain these cases. Thirty-six unrelated patients with the clinical diagnosis of ARPKD were screened for PKHD1 point mutations and copy number variations. Patients without biallelic mutations were re-evaluated and screened for second locus mutations targeted by the phenotype, followed, if negative, by clinical exome sequencing. Twenty-eight patients (78%) carried PKHD1 point mutations, three of whom on only one allele. Two of the three patients harbored in trans either a duplication of exons 33-35 or a large deletion involving exons 1-55. All eight patients without PKHD1 mutations (22%) harbored mutations in other genes (PKD1 (n = 2), HNF1B (n = 3), NPHP1, TMEM67, PKD1/TSC2). Perinatal respiratory failure, a kidney length > +4SD and early-onset hypertension increase the likelihood of PKHD1-associated ARPKD. A patient compound heterozygous for a second and a last exon truncating PKHD1 mutation (p.Gly4013Alafs*25) presented with a moderate phenotype, indicating that fibrocystin is partially functional in the absence of its C-terminal 62 amino acids. We found all ARPKD cases without PKHD1 point mutations to be phenocopies, and none to be explained by biallelic PKHD1 copy number variations. Screening for copy number variations is recommended in patients with a heterozygous point mutation.

Mechanism of pancreatic and liver malformations in human fetuses with short-rib polydactyly syndrome.

The short-rib polydactyly (SRP) syndromes are rare skeletal dysplasias caused by abnormalities in primary cilia, sometimes associated with visceral malformations. The pathogenesis of ductal plate malformation (DPM) varies in different syndromes and has not been investigated in SRP. We have studied liver development in five SRP fetuses and pancreatic development in one SRP fetus, with genetically confirmed mutations in cilia related genes, with and without DPMs, using the immunoperoxidase technique, and compared these to other syndromes with DPM. Acetylated tubulin expression was abnormal in DPM in SRP, Meckel syndrome, and autosomal recessive polycystic kidney disease (ARPKD), confirming ciliary anomalies. SDF-1 was abnormally expressed in SRP and two of three cases of autosomal dominant polycystic kidney disease (ADPKD) but not ARPKD or Meckel. Increased density of quiescent hepatic stellate cells was seen in SRP, Meckel, one of three cases of ARPKD, and two of three cases of ADPKD with aberrant hepatocyte expression of keratin 19 in SRP and ADPKD. Immunophenotypic abnormalities were present even in fetal liver without fully developed DPMs. The SRP case with DPM and pancreatic malformations showed abnormalities in the pancreatic head (influenced by mesenchyme from the septum transversum, similar to liver) but not pancreatic body (influenced by mesenchyme adjacent to the notochord). In SRP, there are differentiation defects of hepatocytes, cholangiocytes, and liver mesenchyme and, in rare cases, pancreatic mesenchymal anomalies. The morphological changes were subtle in early gestation but immunophenotypic abnormalities were present. Mesenchymal-epithelial interactions may contribute to the malformations. Birth Defects Research (Part A) 106:549-562, 2016. © 2016 Wiley Periodicals, Inc.

A labor and cost effective next generation sequencing of PKHD1 in autosomal recessive polycystic kidney disease patients

The Sanger sequencing of patients with recessive polycystic kidney disease is challenging due to the length and heterogeneous mutational spectrum of the PKHD1 gene. Next generation sequencing (NGS) might thus be of special interest to search for PKHD1 mutations. The study involved a total of 22 patients with autosomal recessive polycystic kidney disease (ARPKD) and 8 parents of non-available ARPKD patients. Five pools of 6 samples each were sequenced with the Personal Genome Machine (PGM, Ion Torrent). For each DNA pool, a total of 109 fragments that covered the entire PKHD1 coding sequence were amplified in only two tubes followed by library preparation and NGS with the PGM. To validate the technique, each pool contained the DNA of at least one patient with known mutation. The putative mutations identified in each pool were confirmed and assigned to specific individuals through Sanger sequencing.All but one of the 109 amplicons were successfully read, and we identified the two PKHD1 mutations in 11 of the ARPKD cases, one mutation in 9 patients, and no mutation in only 2 patients. Six of the 8 parents from non-available patients were mutation carriers.The reported procedure would facilitate the large scale analysis of PKHD1 with a significant reduction in cost and labor.

Polycystic kidney disease: genes, proteins, animal models, disease mechanisms and therapeutic opportunities

An increased understanding of the genetic, molecular and cellular mechanisms responsible for the development of polycystic kidney disease has laid out the foundation for the development of rational therapies. Many animal models where these therapies can be tested are currently available. This review summarizes the rationale for these treatments, the results of preclinical trials and the prospects for clinical trials, some already in early phases of implementation.