# Between Crigler-Najjar Syndrome Type II and Gilbert Syndrome: Expanding the Spectrum of Uridine Diphosphate Glucuronosyltransferase 1A1 (UGT1A1)-Related Hyperbilirubinemia

## TL;DR

This paper discusses a case where a newborn with a UGT1A1 gene mutation showed symptoms between two bilirubin-related disorders, highlighting the need for detailed genetic and clinical analysis.

## Contribution

The study presents a novel case showing an intermediate UGT1A1-related hyperbilirubinemia phenotype due to coexisting pathogenic and polymorphic variants.

## Key findings

- The patient exhibited early CNSII-like bilirubin levels but later normalized, resembling GS.
- Compound heterozygosity for UGT1A1 variants likely caused an intermediate phenotype.
- The case supports the view that CNS and GS form a clinical continuum rather than distinct disorders.

## Abstract

Crigler-Najjar syndrome (CNS) and Gilbert syndrome (GS) are inherited non-hemolytic unconjugated hyperbilirubinemias caused by mutations in the uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) gene, resulting in reduced or absent bilirubin conjugation. These disorders form a phenotypic spectrum, with CNS type I (CNSI) representing the most severe form, CNS type II (CNSII) an intermediate phenotype, and GS the mildest. Differentiation between CNSII and GS can be challenging due to overlapping bilirubin levels and genetic variants.

We report the case of a female newborn of Nepali descent who developed jaundice within the first 24 hours of life, requiring multiple courses of phototherapy. Persistent unconjugated hyperbilirubinemia was documented beyond the neonatal period, in the absence of hemolysis or hepatic dysfunction. Genetic testing identified compound heterozygosity for UGT1A1 variants: c.1456T>G (p.Tyr486Asp), associated with CNSII when homozygous, and the promoter polymorphism UGT1A1*28, characteristic of GS. Over time, bilirubin concentrations progressively declined, reaching normal values by 11 months of age, and the patient remained clinically well with normal growth and neurodevelopment.

This case highlights the diagnostic overlap between CNSII and GS, emphasizing the importance of correlating biochemical, genetic, and longitudinal clinical data. The coexistence of pathogenic and polymorphic UGT1A1 variants likely resulted in an intermediate phenotype, with early CNSII-like bilirubin levels followed by normalization consistent with GS. These findings broaden the understanding of the UGT1A1-related hyperbilirubinemia spectrum and reinforce the view that CNS and GS represent a clinical continuum rather than distinct entities. Comprehensive genetic testing and long-term follow-up are essential for accurate diagnosis, prognosis, and family counseling.