Autoimmune hepatitis (AIH) is uncommon enough to meet the usual definition of a rare disease across the world, although the reported figures depend on how actively cases are sought.
How common it is
In the United States the number of people living with AIH is estimated at between 100,000 and 200,000. Its contribution to transplantation is small but steady: 2-3% of paediatric and 4-6% of adult liver transplants in Europe and the United States are performed for AIH. In Europe the prevalence is about 15-20 cases per 100,000 people.
Who is affected
The disease is more common in women. In some regions up to 90% of cases are female, and in most regions more than 60% of new cases are girls, giving a female-to-male ratio of about 3:1.
The age at onset follows a bimodal pattern, with one peak between 10 and 30 years and a second between 40 and 60 years. Because the peaks fall in early adulthood and again in middle age, age alone does not make the diagnosis unlikely in either a young person or an older adult.