Homozygous NEK8 Mutations in Siblings With Neonatal Cholestasis Progressing to End-stage Liver, Renal, and Cardiac Disease

What's new in pediatric genetic cholestatic liver disease: advances in etiology, diagnostics and therapeutic approaches

PURPOSE OF REVIEW

To highlight recent advances in pediatric cholestatic liver disease, including promising novel prognostic markers and new therapies.

FINDINGS

Identification of additional genetic variants associated with progressive familial intrahepatic cholestasis (PFIC) phenotype and new genetic cholangiopathies, with an emerging role of ciliopathy genes. Genotype severity predicts outcomes in bile salt export pump (BSEP) deficiency, and post-biliary diversion serum bile acid levels significantly affect native liver survival in BSEP and progressive familial intrahepatic cholestasis type 1 (FIC1 deficiency) patients. Heterozygous variants in the MDR3 gene have been associated with various cholestatic liver disease phenotypes in adults. Ileal bile acid transporter (IBAT) inhibitors, approved for pruritus in PFIC and Alagille Syndrome (ALGS), have been associated with improved long-term quality of life and event-free survival.

SUMMARY

Next-generation sequencing (NGS) technologies have revolutionized diagnostic approaches, while discovery of new intracellular signaling pathways show promise in identifying therapeutic targets and personalized strategies. Bile acids may play a significant role in hepatic damage progression, suggesting their monitoring could guide cholestatic liver disease management. IBAT inhibitors should be incorporated early into routine management algorithms for pruritus. Data are emerging as to whether IBAT inhibitors are impacting disease biology and modifying the natural history of the cholestasis.

Renal-hepatic-pancreatic dysplasia type 2: Perinatal lethal condition or a multisystemic disorder with variable expressivity

BACKGROUND

Renal-hepatic-pancreatic dysplasia type 2 (RHPD2) is a rare condition that has been described in the literature disproportionately in perinatal losses. The main features of liver and kidney involvement are well described, with cardiac malformations and cardiomyopathy adding additional variation to the phenotype. Many patients reported are within larger cohorts of congenital anomalies of kidney and urinary tract (CAKUT) or liver failure, and with minimal phenotypic and clinical course data.

METHODS

An independent series of phenotypes and prognosis was aggregated from the literature. In this literature review, we describe an additional patient with RHPD2, provide a clinical update on the oldest known living patient, and report the cumulative phenotypes from the existing published patients.

RESULTS

With now examining the 17 known patients in the literature, 13 died within the perinatal period-pregnancy to one year of life. Of the four cases living past the first year of life, one case died at 5 years secondary to renal failure, the other at 30 months secondary to liver and kidney failure. Two are currently alive and well at one year and 13 years. Two cases have had transplantation with one resulting in long-term survival.

CONCLUSIONS

These patients serve to expand the existing phenotype of RHPD2 as a perinatal lethal condition into a pediatric disorder with variable expressivity. Additionally, we introduce the consideration of transplantation and outcomes within this cohort and future patients.

Renal-hepatic-pancreatic dysplasia-1 with a novel NPHP3 genotype: a case report and review of the literature

BACKGROUND

Renal-hepatic-pancreatic dysplasia type 1 (RHPD1) is a rare sporadic and autosomal recessive disorder with unknown incidence. RHPD1 is caused by biallelic pathogenic variants in NPHP3, which encode nephrocystin, an important component of the ciliary protein complex.

CASE PRESENTATION

In this case report, we describe a male newborn who was confirmed by ultrasound to have renal enlargement with multiple cysts, pancreatic enlargement with cysts, and increased liver echogenicity, leading to the clinical diagnosis of RHPD. In addition, a compound heterozygous pathogenic variant, namely, NPHP3 c.1761G > A (p. W587*) and the c.69delC (p. Gly24Ala24*11) variant, was detected by WES. The patient was clinically and genetically diagnosed with RHPD1. At 34 h of life, the infant died of respiratory insufficiency.

CONCLUSION

This is the first published case of RHPD1 in China. This study broadens the known range of RHPD1 due to NPHP3 pathogenic variants.

Defining pathogenicity of NOTCH2 variants for diagnosis of Alagille syndrome type 2 using a large cohort of patients

BACKGROUND AND AIMS

Alagille syndrome (ALGS) type 2 caused by mutations in NOTCH2 has genotypic and phenotypic heterogeneity. Diagnosis in some atypical patients with isolated hepatic presentation could be missed.

METHODS

Using 2087 patients with paediatric liver manifestations, NOTCH2 allele frequencies, in-silico prediction, protein domains and clinical features were analysed to define the pathogenicity of NOTCH2 variants for diagnosis of ALGS type 2.

RESULTS

Among 2087 patients with paediatric liver manifestations, significantly more NOTCH2 variants were absent in gnomAD in patients with elevated γ-glutamyltransferase (GGT) (p = .041). Significantly more NOTCH2 variants which were absent in gnomAD were located in protein functional domains (p = .038). When missense variants were absent in gnomAD and predicted to be pathogenic by at least three out of seven in-silico tools, they were found to be significantly associated with liver manifestations with elevated GGT (p = .003). Comparing this to patients with likely benign (LB) variants, the patients with likely-pathogenic (LP) variants have significantly more liver manifestations with elevated GGT (p = .0001). Significantly more patients with LP variants had extra-hepatic phenotypes of ALGS compared with those patients with LB variants (p = .0004).

CONCLUSION

When NOTCH2 variants are absent in gnomAD, null variants and missense variants which were predicted to be pathogenic by at least three in-silico tools could be considered pathogenic in patients with high GGT chronic liver diseases.

Cholestatic liver diseases of genetic etiology: Advances and controversies

With the application of modern investigative technologies, cholestatic liver diseases of genetic etiology are increasingly identified as the root cause of previously designated "idiopathic" adult and pediatric liver diseases. Here, we review advances in the field enhanced by a deeper understanding of the phenotypes associated with specific gene defects that lead to cholestatic liver diseases. There are evolving areas for clinicians in the current era specifically regarding the role for biopsy and opportunities for a "sequencing first" approach. Risk stratification based on the severity of the genetic defect holds promise to guide the decision to pursue primary liver transplantation versus medical therapy or nontransplant surgery, as well as early screening for HCC. In the present era, the expanding toolbox of recently approved therapies for hepatologists has real potential to help many of our patients with genetic causes of cholestasis. In addition, there are promising agents under study in the pipeline. Relevant to the current era, there are still gaps in knowledge of causation and pathogenesis and lack of fully accepted biomarkers of disease progression and pruritus. We discuss strategies to overcome the challenges of genotype-phenotype correlation and draw attention to the extrahepatic manifestations of these diseases. Finally, with attention to identifying causes and treatments of genetic cholestatic disorders, we anticipate a vibrant future of this dynamic field which builds upon current and future therapies, real-world evaluations of individual and combined therapeutics, and the potential incorporation of effective gene editing and gene additive technologies.

Molecular genetics of renal ciliopathies

Renal ciliopathies are a heterogenous group of inherited disorders leading to an array of phenotypes that include cystic kidney disease and renal interstitial fibrosis leading to progressive chronic kidney disease and end-stage kidney disease. The renal tubules are lined with epithelial cells that possess primary cilia that project into the lumen and act as sensory and signalling organelles. Mutations in genes encoding ciliary proteins involved in the structure and function of primary cilia cause ciliopathy syndromes and affect many organ systems including the kidney. Recognised disease phenotypes associated with primary ciliopathies that have a strong renal component include autosomal dominant and recessive polycystic kidney disease and their various mimics, including atypical polycystic kidney disease and nephronophthisis. The molecular investigation of inherited renal ciliopathies often allows a precise diagnosis to be reached where renal histology and other investigations have been unhelpful and can help in determining kidney prognosis. With increasing molecular insights, it is now apparent that renal ciliopathies form a continuum of clinical phenotypes with disease entities that have been classically described as dominant or recessive at both extremes of the spectrum. Gene-dosage effects, hypomorphic alleles, modifier genes and digenic inheritance further contribute to the genetic complexity of these disorders. This review will focus on recent molecular genetic advances in the renal ciliopathy field with a focus on cystic kidney disease phenotypes and the genotypes that lead to them. We discuss recent novel insights into underlying disease mechanisms of renal ciliopathies that might be amenable to therapeutic intervention.