{{Rsnum
|rsid = 34815109
|Gene=UGT1A10
|Gene_s=UGT1A1,UGT1A3,UGT1A4,UGT1A5,UGT1A6,UGT1A7,UGT1A8,UGT1A9,UGT1A10
|Orientation=plus
|geno1=(-;-)
|geno2=(-;ATAT)
|geno3=(ATAT;ATAT)
|Chromosome=2
|position=233760234
|Assembly=GRCh38
|GenomeBuild=38.1
|dbSNPBuild=141
|Status=Merged
|Merged=3064744
}}Although the insertion is supposed to be the minor allele, the majority of FTDNA v2 and 23andMe v2 results show II as the result, so use caution when interpreting this result.

[[rs34815109]] is one of four SNPs all describing an insertion/deletion polymorphism in the promoter region of the [[UGT1A1]] gene. This gene encodes a protein that modifies hepatic bilirubin in order to allow it to be excreted. SNPs that reduce the activity of the [[UGT1A1]] gene therefore tend to increase serum bilirubin levels.

The [[rs34815109]](TA) allele represents the insertion variant, which actually adds a seventh (TA) pair to what is already a string of six (TA) pairs; this reduces the activity to 30% of normal, and is thus the risk allele. The risk allele is commonly referred to as the UGT1A1*28 allele, and it is homozygous in ~10% of the US population.{{PMID|7565971}}

Risks associated with the [[rs34815109]](TA) allele are almost always associated with the homozygous (TA;TA) genotype, with smaller (or no) effects seen for [[rs34815109]](-;TA) heterozygous carriers. These risks include:

* An increased risk for [[breast cancer]] is reported in premenopausal African-American women, based on a study of 200 women. The reported odds ratio was 1.8 (CI: 1.0-3.1, p=0.06) for carriers of one or more UGT1A1*28 alleles.{{PMID|10706110}}

* In [[colorectal cancer]] patients being treated with [[irinotecan]], adverse side effects (neutropenia and/or severe diarrhea) are reported to be strongly associated with the number of UGT1A1*28 alleles. Patients homozygous for the *28 allele are 3.5 times more likely to develop severe neutropenia compared with individuals with the wild genotype.{{PMID|19125129|OA=1
}} The FDA has approved a genetic test for [[UGT1A1]] status to be used to determine dosage when considering irinotecan therapy [[http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2005/ucm108475.htm FDA press release]]. However, no prospective study has examined whether a reduced dose of irinotecan results in a reduced rate of adverse drug events.{{PMID|19125129|OA=1
}}

* [[Hyperbilirubinemia]], a potentially toxic increase in bilirubin levels, is possible among [[rs34815109]](TA;TA) individuals treated with the drug [[tranilast]].{{PMID|14647407}}

The three other SNPs that describe the same polymorphism are:

* [[rs34983651]]
* [[rs35600288]]
* [[rs5839491]]
{{ neighbor
| rsid = 34983651
| distance = 1
}}
{{ neighbor
| rsid = 5839491
| distance = 5
}}

{{on chip | 23andMe v3}}
{{on chip | 23andMe v4}}