It is caused activity of the enzyme glucuronyltransferase which conjugates bilirubin.Conjugation makes the bilirubin water soluble so that it can be excreted in bile in to the duodenum.The bilirubin level will be less that 6mg/dl. In some patients the bilirubin may be normal. The levels of bilirubin vary daily and seasonally. It is precipitated by dehydration, fasting, menstrual periods or stress.
The patient are usualyy symptomatic less than 30%, sometimes they may have abdominal cramps, fatigue and malaise.