p.Cys223Tyr mutation causing Crigler–Najjar syndrome type II

Abstract

Crigler–Najjar syndrome (CNs) is a rare hereditary unconjugated hyperbilirubinemia caused by mutations in the bilirubin Uridine (UDP) glucuronosyltransferase family 1 member A1 (UGT1A1, ENSG00000241635) gene. Two patients were clinically diagnosed with Crigler–Najjar Syndrome types II (CNs‐II) can be clinically diagnosed which were based on the level of total bilirubin, efficacy of phenobarbital treatment, normal liver architecture and exclusion of hemolysis. Diagnosis was also confirmed by UGT1A1 gene mutations, which by sequencing the coding region for UGT1A1 gene mutations, which were the homozygous mutations c.668G > A/p.Cys223Tyr and which caused less than 10% of activity of the enzyme. No data have been reported about this mutate in the population. These patients have a good prognosis and require no active intervention, indicating that an early accurate diagnosis is necessary for disease management and genetic counseling.

Two patients clinically were diagnosed with Crigler–Najjar syndrome type II (CNs‐II) from one family based on bilirubin levels and partially effective for the phenobarbital treatment, normal liver architecture, and exclusion of hemolysis. Diagnosis was also confirmed by gene analysis and sequencing the coding region for UGT1A1 gene mutations, which were the homozygous mutations c.668G > A/p.Cys223Tyr and which caused less than 10% of activity of the enzyme.

A 21‐year‐old Chinese male was admitted with jaundice. The 15th day after birth, he began to appear icterus; his peak serum total bilirubin (TB) level was 400 μmol/L, and unconjugated bilirubin (UCB) level was 320 μmol/L. Serum bilirubin levels decreased after phototherapy in a local hospital. Jaundice appeared again more than 3 days later, and bilirubin levels fluctuated between 180 and 310 μmol/L and often worsened after infection and fasting.

The proband's father also had unconjugated hyperbilirubinemia from childhood; his level of serum TB fluctuated between 110 and 200 μmol/L but without any treatment. Ultrasonography showed that the liver and spleen were normal.

Laboratory results showed that other measurements of liver function were all in the normal range in the proband and his father. Both the shapes of the red blood cells and erythrocyte osmotic fragility test were normal. Serum TB of proband reduced from 252 to 143.2 μmol/L after treatment with phenobarbital (oral, 30 mg, bid) in our hospital; the proband's mother and brother were found to have normal hematology on normal liver function tests.

On liver biopsy of the proband, the liver architecture was normal. Few or no inflammatory cell infiltrates were observed in the portal tracts, without a lipofuscin‐like pigment [H&E stain, Fig. 1a (200×), and b (400×)]. Hence, Crigler–Najjar Syndrome type II (CNs‐II) can be clinically diagnosed by level of TB and partially effective for the phenobarbital treatment, normal liver architecture and exclusion of hemolysis. ¹

Figure 1.

Liver histology, genetic findings in Proband and his family.

To confirm and complete this diagnose, UDP glucuronosyltransferase family 1 member A1 (UGT1A1) genes (Fig. 1g: the reference sequence) were amplified before Sanger sequencing. A homozygous mutation (c.668G > A) was observed in exon 1 of UGT1A1 gene, causing a cysteine(Cys) → Tyrosine(Tyr) substitution in the propositus (Fig. 1c) and his father(Fig. 1d). His mother (Fig. 1e) and brother (Fig. 1f) both demonstrated heterozygous mutation for c.668G > A/p.Cys223Tyr.

CNs‐II is a rare hereditary unconjugated hyperbilirubinemia caused by mutations in the UGT1A1 gene. ¹ The diagnosis is based on fluctuating unconjugated hyperbilirubinemia and exclusion of hemolysis or liver cell injury; genetic testing is available. ² c.668G > A/p.Cys223Tyr missense mutation in our patients was a new discovery after comparing with the UGT1A1 and common exons allele database (NCBI, HGMD, etc.) up to June 2019. According to the clinical diagnosis of CNs‐II, it can be inferred that the activity of UDP‐glucuronosyltransferase caused by the c.668G > A/p.Cys223Tyr homozygous missense mutation is less than 10% ³ , ⁴ ; however, heterozygous mutation caused deficiency of the enzyme of no more than 30%, ³ , ⁴ so mother and brother did not have unconjugated hyperbilirubinemia.

In conclusion, severe unconjugated hyperbilirubinemia in this family resulted from the homozygous mutations of the p.Cys223Tyr for UGT1A1 gene. These patients generally have a good prognosis.