Udp-Glycosyltransferase 1 Family, Polypeptide A1

Alternative Names

  • UGT1A1
  • Uridine Diphosphate Glycosyltransferase 1 Family, Polypeptide A1
  • Uridine Diphosphate Glycosyltransferase 1
  • UGT1
  • UDP-Glycosyltransferase 1
  • Uridine Diphosphate Glucuronosyltransferase, Bilirubin
  • Bilirubin UDP-Glucuronosyltransferase
  • Udp-Glycosyltransferase 1 Family, Polypeptide A Gene Complex, Included
  • Ugt1a, Included
  • Ugt1a Gene Complex, Included
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OMIM Number

191740

NCBI Gene ID

54658

Uniprot ID

Q9HAW9

Length

13,031 bases

No. of Exons

5

No. of isoforms

2

Protein Name

UDP-glucuronosyltransferase 1A8

Molecular Mass

59742 Da

Amino Acid Count

530

Genomic Location

chr2:233,760,269-233,773,299

Gene Map Locus
2q37.1

Description

This gene encodes a UDP-glucuronosyltransferase, an enzyme of the glucuronidation pathway that transforms small lipophilic molecules, such as steroids, bilirubin, hormones, and drugs, into water-soluble, excretable metabolites. This gene is part of a complex locus that encodes several UDP-glucuronosyltransferases. The locus includes thirteen unique alternate first exons followed by four common exons. Four of the alternate first exons are considered pseudogenes. Each of the remaining nine 5' exons may be spliced to the four common exons, resulting in nine proteins with different N-termini and identical C-termini. Each first exon encodes the substrate binding site, and is regulated by its own promoter. The preferred substrate of this enzyme is bilirubin, although it also has moderate activity with simple phenols, flavones, and C18 steroids. Mutations in this gene result in Crigler-Najjar syndromes types I and II and in Gilbert syndrome. [From RefSeq]

Molecular Genetics

The UGT1A1 gene, which is mutated in Crigler-Najjar syndrome type I, is part of a complex locus that encodes several UDP-glucuronosyltransferases, with a locus that includes thirteen unique alternate first exons followed by four common exons. Four of the alternate first exons are considered pseudogenes. Each of the remaining nine 5' exons may be spliced to the four common exons, resulting in nine proteins with different N-termini and identical C-termini. Each first exon encodes the substrate binding site, and is regulated by its own promoter. The substrate of this enzyme is bilirubin, although it also has moderate activity with simple phenols, flavones, and C18 steroids. UGT1A1 is expressed in the liver only.

Epidemiology in the Arab World

View Map
Variant NameCountryGenomic LocationClinvar Clinical SignificanceCTGA Clinical Significance Condition(s)HGVS ExpressionsdbSNPClinvar
NM_000463.2:c.211G>AUnited Arab EmiratesNC_000002.12:g.233760498G>AAssociation, Benign, Drug Response, Likely Benign, Likely Pathogenic, Pathogenic, Uncertain SignificanceNG_033238.1:g.5226G>A; NM_000463.2:c.211G>A; NP_000454.1:p.Gly71Arg414832312280
NM_000463.2:c.-41_-40dupTAUnited Arab EmiratesNC_000002.12:g.233760235TA[8]Benign, Pathogenic, Uncertain SignificancePathogenicGilbert SyndromeNG_033238.1:g.4963TA[8]; NM_000463.2:c.-41_-40dupTA306474412275
NM_000463.3:c.1073A>GUnited Arab EmiratesNC_000002.12:g.233767925A>GLikely PathogenicCrigler-Najjar Syndrome, Type IING_033238.1:g.12653A>G; NM_000463.3:c.1073A>G; NP_000454.1:p.Asn358Ser886044684
NM_019076.4:c.-41_-40dupUnited Arab EmiratesNC_000002.12:g.233617667_233617668dupPathogenicGilbert SyndromeNG_002601.2:g.32924_32925dup; NM_019076.4:c.-41_-40dup; NP_061949.3:p.?
NM_021027.3:c.983A>GUnited Arab EmiratesNC_000002.12:g.233767161A>GLikely PathogenicPathogenicCrigler-Najjar Syndrome, Type IING_002601.2:g.182418A>G; NM_021027.3:c.983A>G; NP_066307.1:p.Gln328Arg7255134812270

Other Reports

Kuwait

Samilchuk et al. (2001) studied the UGT1A1 gene promoter polymorphism among 55 unrelated Kuwaiti blood donors with G6PD deficiency cased by the Mediterranean mutation, by using PCR followed by polyacrylamide gel electrophoresis (PAGE). Among the 55 studied subjects, nine individuals were found to be homozygous and 26 heterozygous for the (TA)7. The frequencies of the (TA)6 and (TA)7 alleles were 0.6 and 0.4, respectively. Samilchuk et al. (2001) concluded that high frequency of the (TA)7 allele and Mediterranean mutation among Kuwaitis may produce neonatal jaundice in up to 1% of the male and 0.6% of the female newborns.

[Samilchuk E, Al-Suleiman I, Usanga E, Al-Awadi S. UDP Glucuronosyltransferase 1 (UGT1A1) Gene Promoter Polymorphism among Kuwaitis with Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency. Kuwait Med J. 2001, 33 (1):22-25]

Koshy et al. (2004) conducted DNA analysis in affected members of Kuwaiti Bedouin families with Crigler-Najjar syndrome. The patients were found to carry an A-to-G transition converting codon 357 from CAA (gln) to CGA (arg) (Q357R). Furthermore, the patients also carried a TA insertion within the promoter of the UGT1A1 gene.

[See also: Tunisia > Petit et al., 2008].

Tunisia

Labrune et al. (1994) reported two patients from Tunisia with Crigler-Najjar syndrome type I. By DNA analysis they found the mutation Q357R in the two patients. In 2002, Francoual et al. (2002a) studied six patients with Crigler-Najjar syndrome type I who originated from different parts of Tunisia and were not related to each other. In each patient the diagnosis of the disorder was clinically and biochemically suspected, then confirmed by enzymatic assay. The patients were found to carry an A-to-G transition converting codon 357 from CAA (gln) to CGA (arg) (Q357R). Furthermore, the six patients were homozygous for a TA insertion within the promoter of the UGT1A1 gene, thus resulting in TA7/TA7 homozygosity. All 12 parents were heterozygous for the Q357R mutation and the TA7 allele. These resulted indicated that Crigler-Najjar syndrome type I in Tunisia may be associated with a founder effect related to the Q357R mutation within the UGT1 gene. In the same year, Francoual et al. (2002b) reported DNA-based prenatal diagnosis of CN-I in two Tunisian families in whom CN-I patients were diagnosed; thus avoiding the need for enzymatic assay on liver tissue, which requires performing a liver needle biopsy. In both cases, SSCP analysis of fetal DNA showed that the fetus was heterozygous for the Q357R mutation. In both families, the pregnancies were continued.

In order to determine the origin of the c.1070A4G mutation in the UGT1A1 gene, Petit et al. (2008) investigated 21 Tunisian and 2 Kuwaiti Crigler-Najjar type 1 syndrome (CN-1) patients and 28 healthy unrelated Tunisian controls for genetic markers on both centromeric and telomeric sides of c.1070A-G mutation in UGT1A1 gene. The investigation revealed the possibility that this mutation emerged in Bedouin nomad groups and then spread in Tunisia approximately eight centuries ago after the migration of populations from the Middle East to Maghreb. Additionally, clinical and/or biochemical CN-I was genetically confirmed for 56 patients. Twenty-five of these patients originated from different part of Tunisia (Tunis, Sfax and Sousse) and 21 were found to be homozygous for the c.1070A4G mutation in exon 3 associated with the A(TA)7TAA/A(TA)7TAA polymorphism in the TATA box (three of the other patients were found to be homozygous for the deletion c.396_401delCAACAA associated with the A(TA)7TAA/A(TA)7TAA polymorphism and the fourth was found to be homozygous for a large deletion including the promoter and the exon 1. In the Tunisian population, the Gilbert allele A(TA)7TAA frequency was found to be 0.393 and 0.178 for heterozygotes and homozygotes, respectively, comparable to those observed in France and Greece.

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