A Novel Pathogenic UGT1A1 Variant in a Sudanese Child with Type 1 Crigler-Najjar Syndrome

Molecular biology of glucose-6-phosphate dehydrogenase and UDP-glucuronosyltransferase 1A1 in the development of neonatal unconjugated hyperbilirubinemia

Glucose-6-phosphate dehydrogenase (G6PD) deficiency and variants of the UDP-glucuronosyltransferase 1A1 (UGT1A1) gene are the most common genetic causes of neonatal unconjugated hyperbilirubinemia (NUH). In this review, we searched PubMed for articles on the genetic causes of NUH published before December 31, 2022, and analyzed the data. On the basis of the results, we reached eight conclusions: (1) 37 mutations of the G6PD gene are associated with NUH; (2) the clinical manifestation of G6PD deficiency depends not only on ethnicity but also on the molecular mechanisms underlying the deficiency (and thus its severity); (3) of mutations in the UGT1A1 gene, homozygous c.-53A(TA)6TAA > A(TA)7TAA is the main cause of NUH in Caucasians and Africans, whereas homozygous c.211G > A is the main genetic cause of NUH in East Asians; (4) in Indonesian neonates, homozygous c.-3279T > G is the most common cause of NUH development, and neither c.-53 A(TA)6TAA > A(TA)7TAA nor c.211G > A causes it; (5) in breast-fed East Asian neonates, the TA7 repeat variant of the UGT1A1 gene protects against the development of NUH; (6) G6PD deficiency combined with homozygous c.211G > A variation of the UGT1A1 gene increases the risk of severe NUH; (7) in Pakistani and Caucasian patients with Crigler-Najjar syndrome type 2 (CN-2), point mutations of the UGT1A1 gene are widely distributed and frequently occur with variation at nucleotide -53, whereas in Asian patients with CN-2, compound homozygous variations in the coding region are frequently observed; and (8) records of G6PD deficiency and UGT1A1 variation status for a neonate offer useful pharmacogenomic information that can aid long-term care. These results indicate that timely diagnosis of NUH through molecular tests is crucial and that early initiation of treatment for the neonates and educational programs for their parents improves outcomes.

Type II Crigler-Najjar syndrome: a case report and literature review

Background

Crigler-Najjar syndrome (CNS) is caused by mutations in uridine 5'-diphosphate glucuronyltransferase (UGT1A1) resulting in enzyme deficiency and hyperbilirubinemia. Type II CNS patients could respond to phenobarbital treatment and survive. This study presents a rare case of type II CNS.

Case summary

The proband was a 29-year-old male patient admitted with severe jaundice. A hepatic biopsy showed bullous steatosis of the peri-central veins of the hepatic lobule, sediment of bile pigment, and mild periportal inflammation with normal liver plate structure. The type II CNS was diagnosed by routine genomic sequencing which found that the proband with the Gry71Arg/Tyr486Asp compound heterozygous mutations in the UGT1A1 gene. After treatment with phenobarbital (180 mg/day), his bilirubin levels fluctuated between 100 and 200 μmol/L for 6 months and without severe icterus.

Conclusion

Type II CNS could be diagnosed by routine gene sequencing and treated by phenobarbital.

A retrospective cohort analysis of the Yale pediatric genomics discovery program

The Pediatric Genomics Discovery Program (PGDP) at Yale uses next-generation sequencing (NGS) and translational research to evaluate complex patients with a wide range of phenotypes suspected to have rare genetic diseases. We conducted a retrospective cohort analysis of 356 PGDP probands evaluated between June 2015 and July 2020, querying our database for participant demographics, clinical characteristics, NGS results, and diagnostic and research findings. The three most common phenotypes among the entire studied cohort (n = 356) were immune system abnormalities (n = 105, 29%), syndromic or multisystem disease (n = 103, 29%), and cardiovascular system abnormalities (n = 62, 17%). Of 216 patients with final classifications, 77 (36%) received new diagnoses and 139 (64%) were undiagnosed; the remaining 140 patients were still actively being investigated. Monogenetic diagnoses were found in 67 (89%); the largest group had variants in known disease genes but with new contributions such as novel variants (n = 31, 40%) or expanded phenotypes (n = 14, 18%). Finally, five PGDP diagnoses (8%) were suggestive of novel gene-to-phenotype relationships. A broad range of patients can benefit from single subject studies combining NGS and functional molecular analyses. All pediatric providers should consider further genetics evaluations for patients lacking precise molecular diagnoses.