UGT1A1 — Gilbert syndrome and irinotecan response
One copy of the UGT1A1 reduced-function tag variant detected.
You have one working copy and one less-active copy of the UGT1A1 gene.
Tags reduced UGT1A1 activity, consistent with mildly elevated unconjugated bilirubin (Gilbert syndrome pattern). Largely benign on its own; matters if irinotecan chemotherapy is ever prescribed.
You may have slightly higher bilirubin levels on blood tests — a harmless pattern called Gilbert syndrome. On its own this is no problem. It does matter if you're ever prescribed the chemotherapy drug irinotecan, where your dose may need adjusting.
What this means
UGT1A1 conjugates bilirubin (and the chemotherapy drug irinotecan) for excretion. Reduced UGT1A1 activity causes the elevated bilirubin pattern known as Gilbert syndrome — present in ~5–10% of European-descent populations, usually benign and discovered incidentally on a blood test. The same reduction matters in oncology: irinotecan toxicity (neutropenia, diarrhoea) is dose-related to UGT1A1 activity, and CPIC has guidance for reducing irinotecan dose in poor metabolizers.
UGT1A1 is an enzyme that processes bilirubin (a yellow breakdown product of old red blood cells) and the chemotherapy drug irinotecan, getting them ready to leave your body. When the enzyme works less efficiently, bilirubin builds up slightly in your blood — a common, harmless pattern called Gilbert syndrome, which affects roughly 5-10% of people of European descent. Most people only find out they have it through a routine blood test or a faint yellowing of the skin during illness or fasting. The clinically important consequence is for cancer treatment: the chemotherapy drug irinotecan can cause serious side effects (low white blood cells, severe diarrhoea) in people with reduced UGT1A1 activity, so oncologists adjust the dose based on this gene.
Caveats
- Gilbert syndrome itself is benign and requires no treatment.
- The clinically meaningful action is around irinotecan chemotherapy dosing.
- rs887829 is a tag SNP closely linked to the classical *28 promoter repeat variant.