Bilineal inheritance of PKD1 abnormalities mimicking autosomal recessive polycystic disease

Co-Inheritance of Pathogenic Variants in PKD1 and PKD2 Genes Determined by Parental Segregation and De Novo Origin: A Case Report

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disease, and it is typically caused by PKD1 and PKD2 heterozygous variants. Nonetheless, the extensive phenotypic variability observed among affected individuals, even within the same family, suggests a more complex pattern of inheritance. We describe an ADPKD family in which the proband presented with an earlier and more severe renal phenotype (clinical diagnosis at the age of 14 and end-stage renal disease aged 24), compared to the other affected family members. Next-generation sequencing (NGS)-based analysis of polycystic kidney disease (PKD)-associated genes in the proband revealed the presence of a pathogenic PKD2 variant and a likely pathogenic variant in PKD1, according to the American College of Medical Genetics and Genomics (ACMG) criteria. The PKD2 nonsense p.Arg872Ter variant was segregated from the proband's father, with a mild phenotype. A similar mild disease presentation was found in the proband's aunts and uncle (the father's siblings). The frameshift p.Asp3832ProfsTer128 novel variant within PKD1 carried by the proband in addition to the pathogenic PKD2 variant was not found in either parent. This report highlights that the co-inheritance of two or more PKD genes or alleles may explain the extensive phenotypic variability among affected family members, thus emphasizing the importance of NGS-based techniques in the definition of the prognostic course.

Tolvaptan ameliorated kidney function for one elderly autosomal dominant polycystic kidney disease patient: A case report

BACKGROUND

Polycystic kidney disease (PKD) is a genetic disorder characterized by the growth of numerous cysts within the kidneys. Disease progress of some patients often occurs at the early stage. Thus, managing and controlling disease progress is important to slow the kidney function decline especially for the patient with other disorders.

CASE SUMMARY

One 80-year-old male autosomal dominant polycystic kidney disease (ADPKD) patient with chronic kidney disease and other clinical disorders was treated with tolvaptan and edoxaban. Estimated glomerular filtration rate, creatinine and uric acid were monitored during the treatment. In addition, the whole exome sequencing was performed to screen ADPKD genetic variants. The kidney function decline was prevented after using tolvaptan and edoxaban treatment and in the meantime, a venous thromboembolism was removed and leg and pedal edema were alleviated. One mutation c.10102G>A /p.D3368N in the PKD1 gene was identified.

CONCLUSION

Tolvaptan combined with edoxaban administration could delay kidney function decline and eliminate the edema caused by the thromboembolism.

Deep learning is widely applicable to phenotyping embryonic development and disease

Genome editing simplifies the generation of new animal models for congenital disorders. However, the detailed and unbiased phenotypic assessment of altered embryonic development remains a challenge. Here, we explore how deep learning (U-Net) can automate segmentation tasks in various imaging modalities, and we quantify phenotypes of altered renal, neural and craniofacial development in Xenopus embryos in comparison with normal variability. We demonstrate the utility of this approach in embryos with polycystic kidneys (pkd1 and pkd2) and craniofacial dysmorphia (six1). We highlight how in toto light-sheet microscopy facilitates accurate reconstruction of brain and craniofacial structures within X. tropicalis embryos upon dyrk1a and six1 loss of function or treatment with retinoic acid inhibitors. These tools increase the sensitivity and throughput of evaluating developmental malformations caused by chemical or genetic disruption. Furthermore, we provide a library of pre-trained networks and detailed instructions for applying deep learning to the reader's own datasets. We demonstrate the versatility, precision and scalability of deep neural network phenotyping on embryonic disease models. By combining light-sheet microscopy and deep learning, we provide a framework for higher-throughput characterization of embryonic model organisms. This article has an associated 'The people behind the papers' interview.

Cilia and polycystic kidney disease

Polycystic kidney disease (PKD), comprising autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD), is characterized by incessant cyst formation in the kidney and liver. ADPKD and ARPKD represent the leading genetic causes of renal disease in adults and children, respectively. ADPKD is caused by mutations in PKD1 encoding polycystin1 (PC1) and PKD2 encoding polycystin 2 (PC2). PC1/2 are multi-pass transmembrane proteins that form a complex localized in the primary cilium. Predominant ARPKD cases are caused by mutations in polycystic kidney and hepatic disease 1 (PKHD1) gene that encodes the Fibrocystin/Polyductin (FPC) protein, whereas a small subset of cases are caused by mutations in DAZ interacting zinc finger protein 1 like (DZIP1L) gene. FPC is a type I transmembrane protein, localizing to the cilium and basal body, in addition to other compartments, and DZIP1L encodes a transition zone/basal body protein. Apparently, PC1/2 and FPC are signaling molecules, while the mechanism that cilia employ to govern renal tubule morphology and prevent cyst formation is unclear. Nonetheless, recent genetic and biochemical studies offer a glimpse of putative physiological malfunctions and the pathomechanisms underlying both disease entities. In this review, I summarize the results of genetic studies that deduced the function of PC1/2 on cilia and of cilia themselves in cyst formation in ADPKD, and I discuss studies regarding regulation of polycystin biogenesis and cilia trafficking. I also summarize the synergistic genetic interactions between Pkd1 and Pkhd1, and the unique tissue patterning event controlled by FPC, but not PC1. Interestingly, while DZIP1L mutations generate compromised PC1/2 cilia expression, FPC deficiency does not affect PC1/2 biogenesis and ciliary localization, indicating that divergent mechanisms could lead to cyst formation in ARPKD. I conclude by outlining promising areas for future PKD research and highlight rationales for potential therapeutic interventions for PKD treatment.

Monkeys mutant for PKD1 recapitulate human autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) caused by PKD1 mutations is one of the most common hereditary disorders. However, the key pathological processes underlying cyst development and exacerbation in pre-symptomatic stages remain unknown, because rodent models do not recapitulate critical disease phenotypes, including disease onset in heterozygotes. Here, using CRISPR/Cas9, we generate ADPKD models with PKD1 mutations in cynomolgus monkeys. As in humans and mice, near-complete PKD1 depletion induces severe cyst formation mainly in collecting ducts. Importantly, unlike in mice, PKD1 heterozygote monkeys exhibit cyst formation perinatally in distal tubules, possibly reflecting the initial pathology in humans. Many monkeys in these models survive after cyst formation, and cysts progress with age. Furthermore, we succeed in generating selective heterozygous mutations using allele-specific targeting. We propose that our models elucidate the onset and progression of ADPKD, which will serve as a critical basis for establishing new therapeutic strategies, including drug treatments.

Prenatal ultrasonography of autosomal dominant polycystic kidney disease mimicking recessive type: case series

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited renal disease. This pathology has been increasingly diagnosed in utero and several sonographic patterns are well described in the literature.

OBJECTIVE

To present a series of fetuses with an unusual imaging pattern of ADPKD, mimicking autosomal recessive polycystic kidney disease (ARPKD).

MATERIALS AND METHODS

We retrospectively reviewed second-line ultrasound (US) scans performed for suspicion of fetal kidney pathology between 2006 and 2018. Inclusion criteria were (1) proven ADPKD on the basis of a known family history and/or of genetic testing and (2) US features suggestive of ARPKD. We recorded the clinical, imaging, genetic and pathological findings in cases with pregnancy termination.

RESULTS

Three out of 12 patients with proven ADPKD diagnosed in utero presented with US features suggestive of ARPKD. Furthermore, an additional patient observed at another institution was added to the series. History of familial ADPKD was present in three cases. US showed enlarged kidneys with increased cortical echogenicity, decreased corticomedullary differentiation, multiple medullary cysts and decreased amniotic fluid in all four cases. Pregnancy was terminated in two cases (histology confirmed features in keeping with ADPKD), one premature neonate died (histology in progress) and one child is alive. Genetic testing showed a homozygous mutation of the PKD1 gene in two patients, a heterozygous mutation of the PKD1 gene in one patient and was not performed in the remaining patient.

CONCLUSION

This series describes an unusual sonographic prenatal presentation of ADPKD, not yet well described in the radiologic literature, mimicking ARPKD.

Genetic Complexity of Autosomal Dominant Polycystic Kidney and Liver Diseases

Data indicate significant phenotypic and genotypic overlap, plus a common pathogenesis, between two groups of inherited disorders, autosomal dominant polycystic kidney diseases (ADPKD), a significant cause of ESRD, and autosomal dominant polycystic liver diseases (ADPLD), which result in significant PLD with minimal PKD. Eight genes have been associated with ADPKD (PKD1 and PKD2), ADPLD (PRKCSH, SEC63, LRP5, ALG8, and SEC61B), or both (GANAB). Although genetics is only infrequently used for diagnosing these diseases and prognosing the associated outcomes, its value is beginning to be appreciated, and the genomics revolution promises more reliable and less expensive molecular diagnostic tools for these diseases. We therefore propose categorization of patients with a phenotypic and genotypic descriptor that will clarify etiology, provide prognostic information, and better describe atypical cases. In genetically defined cases, the designation would include the disease and gene names, with allelic (truncating/nontruncating) information included for PKD1 Recent data have shown that biallelic disease including at least one weak ADPKD allele is a significant cause of symptomatic, very early onset ADPKD. Including a genic (and allelic) descriptor with the disease name will provide outcome clues, guide treatment, and aid prevalence estimates.

Hyponatremia and cyst growth in neonatal polycystic kidney disease: a case for aquaretics?

Hyponatremia is a common complication in neonatal polycystic kidney disease and is thought to be due to water retention. Aquaretics are drugs that promote free water excretion by blocking the arginine vasopressin receptor type 2 (AVPR2) in the collecting duct and thus impair urinary concentration. AVPR2 is also a key stimulant for cyclic AMP production in the collecting duct and in this way promotes cyst proliferation and pathologic kidney growth in autosomal dominant polycystic kidney disease (ADPKD). Consequently, the aquaretic tolvaptan is now used to slow down progression of ADPKD in adult patients. Whether this beneficial effect on retarding cystic disease progression also extends to recessive forms of polycystic kidney disease (PKD) is currently not known. A recent case report in Pediatric Nephrology touches on the intersecting indications for tolvaptan for both hyponatremia and cyst retardation in neonatal PKD and suggests that use for one indication may have beneficial effects on the other.

Tolvaptan treatment for severe neonatal autosomal-dominant polycystic kidney disease

BACKGROUND

Severe neonatal autosomal-dominant polycystic kidney disease (ADPKD) is rare and easily confused with recessive PKD. Managing such infants is difficult and often unsuccessful.

CASE DIAGNOSIS/TREATMENT

A female infant with massive renal enlargement, respiratory compromise and hyponatraemia was treated with the arginine vasopressin receptor 2 antagonist tolvaptan. This resolved hyponatraemia, and there was no further increase in renal size.

CONCLUSION

Tolvaptan may be a useful treatment for severe neonatal PKD.

TOLVAPTAN USE IN SEVERE NEONATAL AUTOSOMAL DOMINANT POLYCYSTIC KIDNEY DISEASE (ADPKD): THE PHARMACEUTICAL CHALLENGE

BACKGROUND

Unlicensed medications are used all the time in the management of diseases in childhood. Tolvaptan (Jinarc®) is a vasopressin V2-receptor antagonist licensed for use to slow the progression of cyst development and renal insufficiency of ADPKD in adults with CKD stage 1 to 3 with evidence of rapidly progressing disease. Studies of animal models implicate the antidiuretic hormone arginine vasopressin and its messenger cyclic adenosine monophosphate (cAMP) as promoters of kidney-cyst cell proliferation and luminal fluid secretion. The suppression of vasopressin release by means of high water intake, genetic elimination of vasopressin, and vasopressin V2-receptor blockade all reduce the cyst burden and protect kidney function1 A Phase 3 trial showed that Tolvaptan, as compared with placebo, slowed down the increase in total kidney volume and decline in kidney function in adults (average 39 yrs) with ADPKD over a 3-year period.2 ADPKD is the most common form of polycystic kidney disease (PKD) typically late in onset and results from mutation of either of two genes: PKD1 and PKD2. Autosomal recessive polycystic kidney (ARPKD), the other form of PKD, is 20 times less common, presents primarily in infancy and childhood, is typically more severe, and commonly associated with hypertension. ARPKD results from mutation of PKHD1. In spite of these differences, there is growing evidence to suggest that ADPKD and ARPKD are more related than previously suspected.3 Bilineal inheritance of PKD1 abnormalities has been reported to cause extremely severe disease resembling ARPKD.4 The use of Tolvaptan in the management of PKD in children is therefore expected to become more important.

AIM

To describe the first known UK use of Tolvaptan in a neonate with severe ADPKD and the role of the hospital pharmacist in facilitating the use.

METHOD

The role descriptor of hospital pharmacists produced by the World Health Organisation (WHO) was adapted and used to map the pharmaceutical challenges of using Tolvaptan in this child. The descriptor include: (i) Promotion of rational prescribing of drugs, (ii) Use of specialist pharmacists networks to gain greater expertise; (iii) Monitor compliance and therapeutic response and report adverse drug reactions; (iv) ensure supply of high quality products; (v) partake in planning and implementation of clinical trials.

RESULTS

The use of Tolvaptan for indication other than hyponatraemia and other endocrine uses are not routinely commissioned by NHS England. In view of the exceptionality of this case - a severe neonatal form of ADPKD with estimated prevalence of the order of 1 in tens of millions, an Individual Funding Request (IFR) application was made and was approved. The application was supported by financial information provided by the hospital pharmacist who facilitated the application process. Using available information and formulation knowledge, a suspension was eventually recommended and was well tolerated. This resulted in approximately 85% reduction in the cost of treatment over six months. Tolvaptan produced the expected aquaresis and blood pressure reduction. Initial dose of 0.1 mg/kg/day was used and increased according to weight and clinical response. Initial monitoring parameters, which included 4 hourly blood pressure, urine and electrolytes and hepatic function, were recommended. Electrolyte supplements were adjusted accordingly. At 2-month review point, there was no oedema of leg and face but the kidneys were still enlarged. The long term effect on cyst burden and kidney function is being evaluated and will feed into the IFR process.

CONCLUSION

The use of unlicensed medications in children poses a number of pharmaceutical challenges and can be managed through a multidisciplinary approach to treatment intervention. It also re-enforce the paediatric formulation challenge to pharmaceutical companies in which formulation needs are prioritised and existing data are better used to facilitate paediatric formulation development.

Genetics and pathogenesis of autosomal dominant polycystic kidney disease: 20 years on

Autosomal dominant polycystic kidney disease (ADPKD), the most common inherited kidney disorder, is characterized by the progressive development and expansion of bilateral fluid-filled cysts derived from the renal tubule epithelial cells. Although typically leading to end-stage renal disease in late middle age, ADPKD represents a continuum, from neonates with hugely enlarged cystic kidneys to cases with adequate kidney function into old age. Since the identification of the first causative gene (i.e., PKD1, encoding polycystin 1) 20 years ago, genetic studies have uncovered a large part of the key factors that underlie the phenotype variability. Here, we provide a comprehensive review of these significant advances as well as those related to disease pathogenesis models, including mutation analysis of PKD1 and PKD2 (encoding polycystin 2), current mutation detection rate, allelic heterogeneity, genotype and phenotype relationships (in terms of three different inheritance patterns: classical autosomal dominant inheritance, complex inheritance, and somatic and germline mosaicism), modifier genes, the role of second somatic mutation hit in renal cystogenesis, and findings from mouse models of polycystic kidney disease. Based upon a combined consideration of the current knowledge, we attempted to propose a unifying framework for explaining the phenotype variability in ADPKD.

Neonatal polycystic kidney disease

This article provides an up-to-date comprehensive review and summary on neonatal polycystic kidney disease (PKD) with emphasis on the differential diagnosis, clinical manifestations, diagnostic techniques, and potential therapeutic approaches for the major causes of neonatal PKD, namely hereditary disease, including autosomal recessive and autosomal dominant PKD and nonhereditary PKD, with particular emphasis on multicystic dysplastic kidney. A brief overview of obstructive cystic dysplasia and simple and complex cysts is also included.