Autosomal recessive polycystic kidney disease (ARPKD) is the rare and usually early-onset form of polycystic kidney disease with a typical clinical presentation of enlarged cystic kidneys and liver involvement with congenital hepatic fibrosis or Caroli syndrome. ARPKD remains a clinical challenge in pediatrics, frequently requiring continuous and long-term multidisciplinary treatment. In this review, we aim to give an overview over clinical aspects of ARPKD and recent developments in our understanding of disease progression, risk patterns, and treatment of ARPKD.

UNASSIGNED: Autosomal polycystic kidney disease is distinguished into dominant (ADPKD) and recessive (ARPKD) inheritance usually caused by either monoallelic (PKD1/PKD2) or biallelic (PKHD1) germline variation. Clinical presentations are genotype-dependent ranging from fetal demise to mild chronic kidney disease (CKD) in adults. Additionally, exemptions from dominant and recessive inheritance have been reported in both disorders resulting in respective phenocopies. Here, we comparatively report three young adults with microcystic-hyperechogenic kidney morphology based on unexpected genetic alterations beyond typical inheritance.
UNASSIGNED: Next-generation sequencing (NGS)-based gene panel analysis and multiplex ligation-dependent probe amplification (MLPA) of PKD-associated genes, familial segregation analysis, and reverse phenotyping.
UNASSIGNED: Three unrelated individuals presented in late adolescence for differential diagnosis of incidental microcystic-hyperechogenic kidneys with preserved kidney and liver function. Upon genetic analysis, we identified a homozygous hypomorphic PKHD1 missense variant causing pseudodominant inheritance in a family, a large monoallelic PKDH1-deletion with atypical transmission, and biallelic PKD1 missense hypomorphs with recessive inheritance.
UNASSIGNED: By this report, we illustrate clinical presentations associated with atypical PKD-gene alterations beyond traditional modes of inheritance. Large monoallelic PKHD1-alterations as well as biallelic hypomorphs of both PKD1 and PKHD1 may lead to mild CKD in the absence of prominent macrocyst formation and functional liver impairment. The long-term renal prognosis throughout life, however, remains undetermined. Increased detection of atypical inheritance challenges our current thinking of disease ontology not only in PKD but also in Mendelian disorders in general.

Patients referred for HNF1B testing present very heterogeneous phenotypes. Despite suggestive characteristics, many do not harbor mutations in HNF1B. Our objective was to evaluate the clinical characteristics of probands referred for HNF1B genetic testing through a nationwide monogenic diabetes screening program.
Probands tested for HNF1B mutations in the 2005-2018 period (N = 50) were identified in the Polish Monogenic Diabetes Registry, which prospectively recruits primarily pediatric patients and their families on a nationwide scale. Variants that had been reported pathogenic were reassessed using criteria of the American College of Medical Genetics and Genomics (ACMG). A structured medical interview was performed with all available individuals, their parents, and/or their physicians. For each patient, HNF1B score was calculated based on available clinical information.
The study group numbered 36 unrelated probands (28% lost to follow-up): 14 with pathogenic or likely-pathogenic variants in HNF1B, one with a variant of uncertain significance, and 21 negative for HNF1B mutations. Presence of cystic kidneys (OR = 9.17, 95% CI:1.87-44.92), pancreatic abnormalities (OR = 15, 95% CI:1.55-145.23), elevated liver enzymes (OR = 15, 95% CI:1.55-145.23) best discriminated HNF1B-positive cases from the negative ones. Presence of impaired glucose tolerance coupled with kidney disease in the proband and one parent was also highly predictive for HNF1B mutations (OR = 11.11, 95% CI:1.13-109.36). HNF1B-score with recommended cutoff distinguished patients with and without HNF1B findings with 100% sensitivity and 47.6% specificity. Addition of four clinical variables to select patients based on HNF1B score improved specificity to 71.4% (95% CI:47.8%-88.7%) while retaining 100% sensitivity.
Detailed medical interview may enable more accurate patient selection for targeted genetic testing.

Meckel syndrome (MKS) is a perinatally lethal, genetically heterogeneous, autosomal recessive condition caused by defective primary cilium formation leading to polydactyly, multiple cysts in kidneys and malformations of nervous system. We performed exome sequencing in six fetuses from six unrelated families with MKS. We identified seven novel variants in B9D2, TNXDC15, CC2D2A, CEP290 and TMEM67. We describe the second family with MKS due to a homozygous variant in B9D2 and fifth family with bi-allelic variant in TXNDC15. Our data validates the causation of MKS by pathogenic variation in B9D2 and TXNDC15 and also adds novel variants in CC2D2A, CEP290 and TMEM67 to the literature.

Walker-Warburg syndrome (WWS) is a severe form of congenital muscular dystrophy secondary to α-dystroglycanopathy with muscle, brain, and eye abnormalities often leading to death in the first weeks of life. It is transmitted in an autosomal recessive pattern, and has been linked to at least 15 different genes; including protein O-mannosyltransferase 1 (POMT1), protein O-mannosyltransferase 2 (POMT2), protein O-mannose beta-1,2-N acetylglucosaminyltransferase (POMGNT1), fukutin (FKTN), isoprenoid synthase domain-containing protein (ISPD), and other genes. We report on a consanguineous family with four consecutive siblings affected by this condition with lethal outcome in three (still birth), and termination of the fourth pregnancy based on antenatal MRI identification of brain and kidney anomalies that heralded proper and deep clinical phenotyping. The diagnosis of WWS was suggested based on the unique collective phenotype comprising brain anomalies in the form of lissencephaly, subcortical/subependymal heterotopia, and cerebellar hypoplasia shared by all four siblings; microphthalmia in one sibling; and large cystic kidneys in the fetus and another sibling. Other unshared neurological abnormalities included hydrocephalus and Dandy-Walker malformation. Whole exome sequencing of the fetus revealed a highly conserved missense mutation in POMT2 that is known to cause WWS with brain and eye anomalies.In conclusion, the heterogeneous clinical presentation in the four affected conceptions with POMT2 mutation expands the current clinical spectrum of POMT2-associated WWS to include large cystic kidneys; and confirms intra-familial variability in terms of brain, kidney, and eye anomalies.

BACKGROUND: Neonatal autosomal recessive polycystic kidney disease (ARPKD) is associated with giant kidneys, lung hypoplasia, pulmonal hypertension, and end-stage renal failure. Depending on the study, mortality is reported to range between 20 and 80%.
OBJECTIVE: Does bilateral nephrectomy improve survival?
METHODS: Between 2010 and 2016, we treated 7 children with prenatally diagnosed ARPKD. All had a planned delivery by cesarean section. After birth, oscillated ventilation with nitrogen enrichment was initiated to achieve maximum oxygenation and to decrease pumonary hypertension. All children had bilateral massive kidney hyperplasia (length 13-16 cm).
RESULTS: Nephrectomy on one side was performed within 72 h together with placement of a peritoneal dialysis catheter in the intensive care unit. Contralateral nephrectomy was performed after 1-2 weeks when the child was stabilized by dialysis. In 2 children, kidney transplantation has already been performed and they are doing fine. One child died after 10 months due to infection. The other children are stable on home peritoneal dialysis awaiting transplantation.
CONCLUSIONS: Early bilateral nephrectomy in neonatal ARPKD is feasible, but requires distinctive care at a pediatric intensive care unit and a high amount of organizational efforts to treat these children adequately in the first few days. In our experience, the procedure is a promising approach to improve ventilation and enable dialysis. However, kidney transplantation, best from a living donor, is required within the first years of life.

OBJECTIVE: The studies were designed to test the efficacy of two peroxisome proliferator-activated receptor γ (PPARγ) agonists in two rodent models of polycystic kidney disease (PKD).
METHODS: The PCK rat is a slowly progressing cystic model while the Wpk-/- rat is a rapidly progressing model. PCK rats were fed with a pharmacological (0.4 mg/kg body weight [BW]) and a sub-pharmacological (0.04 mg/kg BW) dose of rosiglitazone (week 4-28). Wpk-/- rats were fed with pharmacological (2.0 mg/kg BW) and sub-pharmacologic (0.2 mg/kg BW) doses of pioglitazone from day 5 to 18. At termination, kidney weights of treated versus untreated cystic animals were used to determine efficacy. The current studies were also compared with previous studies containing higher doses of PPARγ agonists. The concentrations used in the animals were calculated with reference to equivalent human doses for both drugs.
RESULTS: The current studies demonstrate: 1) that low, pharmacologically relevant, doses of the PPARγ agonists effectively inhibit cyst growth; 2) there is a class action of the drugs with both commercially available PPARγ agonists, rosiglitazone, and pioglitazone, inhibiting cyst growth; 3) the drugs showed efficacy in two different preclinical cystic models. In the PCK rat, animals fed with a sub-pharmacological dose of rosiglitazone for 24 weeks had significantly lower kidney weights than untreated animals (3.68 ± 0.13 g vs. 4.17 ± 0. 11 g, respectively, P < 0.01) while treatment with a pharmacologic dose had no significant effect on kidney weight. The rapidly progressing Wpk-/- rats were fed with pharmacological and sub-pharmacologic doses of pioglitazone from day 5 to 18 and the kidneys were compared with non-treated, cystic animals. Kidney weights on the pharmacologic dose were not statistically lower than the untreated animals while rats fed a sub-pharmacologic dose showed a significant decrease compared with untreated animals (3.35 ± 0.15 g vs. 4.55 ± 0.46 g, respectively, P = 0.045).
CONCLUSIONS: Concentrations of PPARγ agonists below the human equivalent diabetic doses are effective in slowing cyst growth in two rodent models of PKD.

Meckel-Gruber syndrome (MGS) is an autosomal recessive disorder characterized by occipital encephalocele, polycystic kidneys and variable other congenital malformations. We report on a Sudanese patient with MGS diagnosed by antenatal ultrasound scan. Pregnancy was terminated at 25 weeks of gestation.

Heterozygous mutations of the HNF1B gene are the commonest known monogenic cause of developmental kidney disease. Half of patients have a deletion (approximately 1.3 Mb) of chromosome 17q12, encompassing HNF1B plus 14 additional genes. This 17q12 deletion has been linked with an increased risk of neurodevelopmental disorders, such as autism. Here we compared the neurodevelopmental phenotype of 38 patients with HNF1B-associated renal disease due to an intragenic mutation in 18 patients or due to 17q12 deletion in 20 patients to determine whether haploinsufficiency of HNF1B is responsible for the neurodevelopmental phenotype. Significantly, brief behavioral screening in children with the deletion showed high levels of psychopathology and its impact. Eight individuals (40%) with a deletion had a clinical diagnosis of a neurodevelopmental disorder compared to none with an intragenic mutation. The 17q12 deletions were also associated with more autistic traits. Two independent clinical geneticists were able to predict the presence of a deletion with a sensitivity of 83% and specificity of 79% when assessing facial dysmorphic features as a whole. Thus, the 17q12 deletions but not HNF1B intragenic mutations are associated with neurodevelopmental disorders. Hence, the HNF1B gene is not involved in the neurodevelopmental phenotype of these patients. Nephrologists need to be aware of this association to ensure appropriate referral to psychiatric services.