Certain heterozygous variants in the kinase domain of the serine/threonine kinase NEK8 can cause an autosomal dominant form of polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) resulting from pathogenic variants in PKD1 and PKD2 is the most common form of PKD, but other genetic causes tied to primary cilia function have been identified. Biallelic pathogenic variants in the serine/threonine kinase NEK8 cause a syndromic ciliopathy with extra-kidney manifestations. Here we identify NEK8 as a disease gene for ADPKD in 12 families. Clinical evaluation was combined with functional studies using fibroblasts and tubuloids from affected individuals. Nek8 knockout mouse kidney epithelial (IMCD3) cells transfected with wild type or variant NEK8 were further used to study ciliogenesis, ciliary trafficking, kinase function, and DNA damage responses. Twenty-one affected monoallelic individuals uniformly exhibited cystic kidney disease (mostly neonatal) without consistent extra-kidney manifestations. Recurrent de novo mutations of the NEK8 missense variant p.Arg45Trp, including mosaicism, were seen in ten families. Missense variants elsewhere within the kinase domain (p.Ile150Met and p.Lys157Gln) were also identified. Functional studies demonstrated normal localization of the NEK8 protein to the proximal cilium and no consistent cilia formation defects in patient-derived cells. NEK8-wild type protein and all variant forms of the protein expressed in Nek8 knockout IMCD3 cells were localized to cilia and supported ciliogenesis. However, Nek8 knockout IMCD3 cells expressing NEK8-p.Arg45Trp and NEK8-p.Lys157Gln showed significantly decreased polycystin-2 but normal ANKS6 localization in cilia. Moreover, p.Arg45Trp NEK8 exhibited reduced kinase activity in vitro. In patient derived tubuloids and IMCD3 cells expressing NEK8-p.Arg45Trp, DNA damage signaling was increased compared to healthy passage-matched controls. Thus, we propose a dominant-negative effect for specific heterozygous missense variants in the NEK8 kinase domain as a new cause of PKD.

The Search for Biomarkers to Aid in Diagnosis, Differentiation, and Prognosis of Childhood Idiopathic Nephrotic Syndrome.

Identification of genes associated with childhood-onset nephrotic syndrome has significantly advanced our understanding of the pathogenesis of this complex disease over the past two decades, however the precise etiology in many cases remains unclear. At this time, we still rely on invasive kidney biopsy to determine the underlying cause of nephrotic syndrome in adults. In children, response to steroid therapy has been shown to be the best indicator of prognosis, and therefore all children are treated initially with corticosteroids. Because this strategy exposes a large number of children to the toxicities of steroids without providing any benefit, many researchers have sought to find a marker that could predict a patient's response to steroids at the time of diagnosis. Additionally, the identification of such a marker could provide prognostic information about a patient's response to medications, progression to end stage renal disease, and risk of disease recurrence following transplantation. Major advances have been made in understanding how genetic biomarkers can be used to predict a patient's response to therapies and disease course, especially after transplantation. Research attempting to identify urine- and serum-based biomarkers which could be used for the diagnosis, differentiation, and prognosis of nephrotic syndrome has become an area of emphasis. In this review, we explore the most exciting biomarkers and their potential clinical applications.

Kidney biopsy findings in children with sickle cell disease: a Midwest Pediatric Nephrology Consortium study.

BACKGROUND: Renal damage is a progressive complication of sickle cell disease (SCD). Microalbuminuria is common in children with SCD, while a smaller number of children have more severe renal manifestations necessitating kidney biopsy. There is limited information on renal biopsy findings in children with SCD and subsequent management and outcome. METHODS: This is a multicenter retrospective analysis of renal biopsy findings and clinical outcomes in children and adolescents with SCD. We included children and adolescents (age ≤ 20 years) with SCD who had a kidney biopsy performed at a pediatric nephrology unit. The clinical indication for biopsy, biopsy findings, subsequent treatments, and outcomes were analyzed. RESULTS: Thirty-six SCD patients (ages 4-19 years) were identified from 14 centers with a median follow-up of 2.6 years (0.4-10.4 years). The indications for biopsy were proteinuria (92%) and elevated creatinine (30%). All biopsies had abnormal findings, including mesangial hypercellularity (75%), focal segmental glomerulosclerosis (30%), membranoproliferative glomerulonephritis (16%), and thrombotic microangiopathy (2%). There was increased use of hydroxyurea, angiotensin-converting-enzyme inhibitors, and angiotensin receptor blockers following renal biopsy. At last follow-up, 3 patients were deceased, 2 developed insulin-dependent diabetes mellitus, 6 initiated chronic hemodialysis, 1 received a bone marrow transplant, and 1 received a kidney transplant. CONCLUSIONS: Renal biopsies, while not commonly performed in children with SCD, were universally abnormal. Outcomes were poor in this cohort of patients despite a variety of post-biopsy interventions. Effective early intervention to prevent chronic kidney disease (CKD) is needed to reduce morbidity and mortality in children with SCD.

Bleeding Complications after Pediatric Kidney Biopsy: A Systematic Review and Meta-Analysis.

BACKGROUND AND OBJECTIVES: Kidney biopsy is an essential tool for the diagnosis and treatment of patients with kidney disease; however, because of its invasive nature, bleeding complications may arise. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We performed a meta-analysis of prospective or retrospective observational studies and randomized, controlled trials in pediatric patients undergoing native or transplant kidney biopsy in an inpatient or outpatient setting in MEDLINE-indexed studies from January 1998 to November 1, 2017 to determine the proportion of patients who develop hematoma, need blood transfusion, or need an additional intervention due to a complication after kidney biopsy. RESULTS: Twenty-three studies of 5504 biopsies met inclusion criteria. The proportion of patients developing hematoma after biopsy was between 11% (95% confidence interval, 7% to 17%) and 18% (95% confidence interval, 9% to 35%) using two analyses that included different time periods. The proportion needing blood transfusion was 0.9% (95% confidence interval, 0.5% to 1.4%). The proportion needing an additional intervention due to postbiopsy complication was 0.7% (95% confidence interval, 0.4% to 1.1%). Secondary analysis was not possible due to lack of data in the original manuscripts on laboratory values, needle gauges, number of needle passes, age of patient, or performer (attending versus trainee). Analysis with metaregression found that use of real-time ultrasound during biopsy did not modify the risk for hematoma, requirement of a blood products transfusion, or requirement of an additional procedure after biopsy. Analysis with metaregression comparing native biopsies with transplant biopsies did not reveal that biopsy type (native kidney biopsy versus transplant kidney biopsy) was associated with the need for a blood transfusion or requirement of an additional intervention after biopsy. CONCLUSIONS: The development of perinephric hematoma after kidney biopsy is not an infrequent finding. The proportion of patients requiring blood transfusion or needing an additional intervention as a result of kidney biopsy in pediatric patients is significantly smaller.