Follow-up of patients with juvenile nephronophthisis after renal transplantation: a single center experience

Clinical report and genetic analysis of rare premature infant nephronophthisis caused by biallelic TTC21B variants

BACKGROUND

Nephronophthisis (NPHP) is a genetically heterogeneous disease that can lead to end-stage renal disease (ESRD) in children. The TTC21B variant is associated with NPHP12 and mainly characterized by cystic kidney disease, skeletal malformation, liver fibrosis, and retinopathy. Affected patients range from children to adults. Some patients experience ESRD in infancy or early childhood, but clinical reports on neonatal patients are rare. We report a case of NPHP12 in a premature infant and analyze its genetic etiology.

METHODS

Trio-whole exome sequencing analysis was performed on the patient and her parents; bioinformatics software was used to predict and analyze the hazards of the variants. Sanger sequencing was performed to verify variants. We calculated the free energy between mutant IFT139 and the IFT121-IFT122-IFT43 complex structure using molecular dynamics (MD). Finally, the clinical and genetic characteristics of patients with hotspot variant Cys518Arg were reviewed.

RESULTS

Genetic analysis revealed compound-heterozyous TTC21B variants in the patient, c.497delA (p.Lys166fs*36) and c.1552T>C (p.Cys518Arg). Her father and mother had heterozygous c.497delA (p.Lys166fs*36) and heterozygous c.1552T>C (p.Cys518Arg), respectively. Cys518Arg represents a hotspot variant, and the MD calculation results show that this can reduce the structural stability of the IFT121-IFT122-IFT139-IFT43 complex structure. A literature review showed that Cys518Arg might lead to the early occurrence of ESRD.

CONCLUSIONS

Compound-heterozygous TTC21B variants underlie the phenotype in this patient. Thus, Cys518Arg may be a hotspot variant in the Chinese population. Genetic testing should be recommended for NPHP in neonates and early infants.

Phenotype Spectrum in Tunisian Population with NPHP1 Deletion

Introduction

Nephronophthisis (NPHP) is a tubulointerstitial kidney disorder with an autosomal recessive inheritance pattern. Its genetic heterogeneity contributes to phenotype variability. The most frequent etiology of juvenile nephronophthisis is a mutation in the nephronophthisis type 1 (NPHP1) gene. This study aimed to evaluate the genotype-phenotype correlation in NPHP1 gene mutation.

Methods

A multicenter retrospective study was performed over 20 years from 1998 to 2018 to describe the clinical, biological, and radiological features associated with the large deletion NPHP1 gene in 32 patients.

Results

The incidence of NPHP1 was 1.6/204041. Eighty-one percent of our patients were born out of consanguineous marriages. The mean age at diagnosis was 14 ± 7 years. The patients were divided into three groups: isolated nephronophthisis (72%), syndromic nephronophthisis (19%), and patients without recognizable syndrome (9%). Intrafamilial and geographical variability was observed in syndrome diagnoses and in age at the onset of CKD stage 5. Genotype frequency varied between 50% and 100% in genealogical data. Juvenile (47%), adolescent (37%), and adult (13%) clinical forms have been distinguished by the onset of CKD stage 5. The five-year survival rate of renal transplantation was 80%.

Conclusion

Given the broad clinical spectrum of NPHP1 associated with the large deletion of the NPHP1 gene, no genotype-phenotype correlation could be established.

Pathogenic Variants in CEP290 or IQCB1 Cause Earlier-Onset Retinopathy in Senior-Loken Syndrome Compared to Those in INVS, NPHP3, or NPHP4

PURPOSE

Senior-Loken syndrome (SLSN) is an autosomal recessive disorder characterized by retinopathy and nephronophthisis. This study aimed to evaluate whether different phenotypes are associated with different variants or subsets of 10 SLSN-associated genes based on an in-house data set and a literature review.

DESIGN

Retrospective case series.

METHODS

Patients with biallelic variants in SLSN-associated genes, including NPHP1, INVS, NPHP3, NPHP4, IQCB1, CEP290, SDCCAG8, WDR19, CEP164, and TRAF3IP1, were recruited. Ocular phenotypes and nephrology medical records were collected for comprehensive analysis.

RESULTS

Variants in 5 genes were identified in 74 patients from 70 unrelated families, including CEP290 (61.4%), IQCB1 (28.6%), NPHP1 (4.2%), NPHP4 (2.9%), and WDR19 (2.9%). The median age at the onset of retinopathy was approximately 1 month (since birth). Nystagmus was the most common initial sign in patients with CEP290 (28 of 44, 63.6%) or IQCB1 (19 of 22, 86.4%) variants. Cone and rod responses were extinguished in 53 of 55 patients (96.4%). Characteristic fundus changes were observed in CEP290- and IQCB1-associated patients. During follow-up, 70 of the 74 patients were referred to nephrology, among whom nephronophthisis was not detected in 62 patients (88.6%) at a median age of 6 years but presented in 8 patients (11.4%) aged approximately 9 years.

CONCLUSIONS

Patients with pathogenic variants in CEP290 or IQCB1 presented early with retinopathy, whereas other patients with INVS, NPHP3, or NPHP4 variants first developed nephropathy. Therefore, awareness of the genetic and clinical features may facilitate the clinical management of SLSN, especially early intervention of kidney problems for patients with eyes affected first.

Renal ciliopathies: promising drug targets and prospects for clinical trials

INTRODUCTION

Renal ciliopathies represent a collection of genetic disorders characterized by deficiencies in the biogenesis, maintenance, or functioning of the ciliary complex. These disorders, which encompass autosomal dominant polycystic kidney disease (ADPKD), autosomal recessive polycystic kidney disease (ARPKD), and nephronophthisis (NPHP), typically result in cystic kidney disease, renal fibrosis, and a gradual deterioration of kidney function, culminating in kidney failure.

AREAS COVERED

Here we review the advances in basic science and clinical research into renal ciliopathies which have yielded promising small compounds and drug targets, within both preclinical studies and clinical trials.

EXPERT OPINION

Tolvaptan is currently the sole approved treatment option available for ADPKD patients, while no approved treatment alternatives exist for ARPKD or NPHP patients. Clinical trials are presently underway to evaluate additional medications in ADPKD and ARPKD patients. Based on preclinical models, other potential therapeutic targets for ADPKD, ARPKD, and NPHP look promising. These include molecules targeting fluid transport, cellular metabolism, ciliary signaling and cell-cycle regulation. There is a real and urgent clinical need for translational research to bring novel treatments to clinical use for all forms of renal ciliopathies to reduce kidney disease progression and prevent kidney failure.

A single heterozygous nonsense mutation in the TTC21B gene causes adult-onset nephronophthisis 12: A case report and review of literature

BACKGROUND

Nephronophthisis type 12 (NPHP 12) is a rare cilia-related cystic kidney disease, caused by TTC21B mutation, mainly involving the kidneys, which generally occurs in children. Our study aimed to illustrate its clinical, pathological and genetic characteristics by reporting an adult-onset case of NPHP 12 caused by a single heterozygous nonsense mutation of TTC21B confirmed by renal histology and whole exome sequencing and reviewing related literature with a comparative analysis of the clinical features of each case. It will further increase the recognition of this rare kidney genetic disease, which sometimes can manifest as an adult disease.

RESULTS

A 33-years-old man showed a chronic disease course, and he exhibited slight renal dysfunction (CKD stage 3, eGFR = 49 ml/[min* 1.73 m2]) with renal tubular proteinuria, without any extrarenal manifestations, congenital malformation history of kidney disease, or family hereditary disease. Renal histological findings showed substantial interstitial fibrosis with some irregular and tortuous tubules with complex branches and segmental thickening and splitting of the tubular basement membrane. The patient was diagnosed with chronic interstitial nephritis for an unknown reason clinically. Further genetic analysis revealed a single heterozygous nonsense mutation in the TTC21B gene and NPHP 12 was diagnosed finally.

CONCLUSION

A single heterozygous mutation in the TTC21B gene may cause atypical NPHP12, which had a relatively later onset and milder clinical symptoms without developmental abnormalities. Therefore, for unexplained adult-onset chronic interstitial nephritis with unusual changes of renal tubules and interstitial fibrosis, even without a clear history of hereditary kidney disease, genetic testing is still recommended. The correct diagnosis of this rare adult-onset hereditary nephropathy can avoid unnecessary treatment.

Long-Term Outcomes of Kidney Transplant Recipients With Juvenile Nephronophthisis

OBJECTIVES

Nephronophthisis is the most common genetic cause of kidney failure in childhood. Treatment for nephronophthisis is symptomatic, and kidney transplant is a good treatment option when kidney failure has developed. We reported the outcomes of kidney transplant recipients with primary diagnosis of juvenile nephronophthisis who were followed-up in our center.

MATERIALS AND METHODS

We retrospectively examined medical records of 17 kidney transplant patients with a primary diagnosis of juvenile nephronophthisis. We compared this group of 17 patients with kidney transplant recipients who had other etiologies of kidney failure in terms of transplant age, donor type, immunosuppressive treatment, acute rejection, graft loss rates, and glomerular filtration rates at 1 and 5 years posttransplant (N = 180 total analyzed).

RESULTS

Among 180 kidney transplant recipients, the 17 patients (9.4%) with nephronophthisis had a mean age of 12.6 ± 4.3 years and mean follow-up time posttransplant of 79.5 ± 41.9 months. Five of 17 patients received a kidney transplant from a deceased donor (29.4%), and the remaining 12 patients (70.6%) received transplants from living related donors. Preemptive kidney transplant was performed in 4 patients (23.5%). There was a statistically significant difference (P < .05) in terms of acute rejection between patients with nephronophthisis (17.6%) versus patients with other primary diagnoses (34%). However, the patients with nephronophthisis versus those with other primary diagnoses were similar (P > .05) in terms of transplant age (12.6 ± 4.3 vs 13.8 ± 6.7 years, respectively) and follow-up time (79.5 ± 41.9 vs 59.1 ± 38.8 months, respectively). Donor type, immunosuppressive treatment, and 1-year (96.7 ± 23.2 vs 97.6 ± 28.4 mL/min/1.73 m2) and 5-year (84.7 ± 31.1 vs 86.7 ± 21.7 mL/min/1.73 m2) glomerular filtration rates were also similar (P > .05) between groups.

CONCLUSIONS

Posttransplant prognosis was good among kidney transplant recipients with juvenile nephronophthisis.

Renal Ciliopathies: Sorting Out Therapeutic Approaches for Nephronophthisis

Nephronophthisis (NPH) is an autosomal recessive ciliopathy and a major cause of end-stage renal disease in children. The main forms, juvenile and adult NPH, are characterized by tubulointerstitial fibrosis whereas the infantile form is more severe and characterized by cysts. NPH is caused by mutations in over 20 different genes, most of which encode components of the primary cilium, an organelle in which important cellular signaling pathways converge. Ciliary signal transduction plays a critical role in kidney development and tissue homeostasis, and disruption of ciliary signaling has been associated with cyst formation, epithelial cell dedifferentiation and kidney function decline. Drugs have been identified that target specific signaling pathways (for example cAMP/PKA, Hedgehog, and mTOR pathways) and rescue NPH phenotypes in in vitro and/or in vivo models. Despite identification of numerous candidate drugs in rodent models, there has been a lack of clinical trials and there is currently no therapy that halts disease progression in NPH patients. This review covers the most important findings of therapeutic approaches in NPH model systems to date, including hypothesis-driven therapies and untargeted drug screens, approached from the pathophysiology of NPH. Importantly, most animal models used in these studies represent the cystic infantile form of NPH, which is less prevalent than the juvenile form. It appears therefore important to develop new models relevant for juvenile/adult NPH. Alternative non-orthologous animal models and developments in patient-based in vitro model systems are discussed, as well as future directions in personalized therapy for NPH.