Genetic Diagnosis Of20Cases With Congenital Indirect Hyperbilirubinemia

Objective The hereditary unconjugated hyperbilirubinemias is caused by the mutation in UGTIAI gene. The decrease or lack of bilirubin uridine diphosphate glucuronyl transferase enzyme in the liver endoplasmic reticulum leads to the difficulties of unconjugated bilirubin glucuronidation, which result in the hereditary unconjugated hyperbilirubinemias. According to the bilirubin-glucuronidation activity, the hereditary unconjugated hyperbilirubinemia can be divided into Crigler-Najjar syndrome type I(CNS I), Crigler-Najjar syndrome type Ⅱ (CN-Ⅱ), and Gilbert’s syndrome (GS). The patients are characterized by yellow skin or yellow sclera. The diagnosis is mainly based on the molecular genetic tests, however, there is no large study in patients with hereditary unconjugated hyperbilirubinemias diagnosed by molecular genetic tests. In this study, based on the genetic diagnosis of our patients, we tried to research Chinese patients’common mutations and genetic spectrum, discussing the relationship between phenotype and genotype and had a better understanding of this disorder.Methods Total genomic DNA was extracted from peripheral blood leukocytes of the20patients and18parents. The promoter region and coding exons1-5of the UGTIA1gene were amplified by polymerase chain reaction (PCR) and sequenced directly.Results15mutations were detected in20patients, nine of them were known mutations, and the others we found were new mutations for the first time, including four kinds of missense mutations:c.185C>T p.P62L, c.669C>Gp.C223W, c.1061G> T p.W354L, c.1156G> T p.V386F; one nonsense mutations:c.1567C> T p.R523X and one deletion mutations:c.1047de1G p.T349TfsX16.40alleles in20patients were detected out of55mutations,15genotypes. GS in patients with mutations in the TATA box insertional mutagenesis-based multi-compound heterozygous mutation in the form of existence.11cases of patients with CNS number of mutations and genotype more main p.G71R and p.Y486D mutation, seven cases were detected in four disease-causing mutation, five cases of patients with composite pure and mutant forms.Conclusions(1) mutations were found in all the20patients with congenital indirect hyperbilirubinemia in UGT1A1gene, and mutation detection was100%, including six kinds of new mutations reported for the first time, the expansion of the UGT1A1gene mutationspectrum.(2) The study shows that p.G71R, p.Y486D and TATA box insertion mutation are the hotspots. And the promoter region, the first and fifth exon region are the hot spot areas.(3)The promoter TATA box repeatation, especially the homozygous TATA box is more inclined in the GS.(4) The quantity of mutations may be associated with clinical phenotypes. When the number is up to four, especially the existence p.G71R/p.Y486D compound homozygous, the patients appear much more associated with Crigler-Najjar syndrome type Ⅱ.(5) The diagnosis of this disorder should be combined with the clinical tests and genetic test.