Autoimmune hepatitis (AIH) is an immune-mediated and inflammatory liver disorder. It is currently divided into types 1 and 2, differentiated and defined by the presence of specific autoantibodies. The objectives are to describe the prevalence and incidence of type 1 and 2 autoimmune hepatitis and to analyze the clinics, biochemical and histopathological profiles at diagnosis and follow-up, initial therapy, response to therapy and long-term follow-up in three Italian centers of patients with type 1 and type 2 AIH.

Background: Autoimmune hepatitis (AIH) is an immune-mediated and inflammatory liver disorder with typical onset in pediatric age. It is currently divided into types 1 and 2, differentiated and defined by the presence of specific autoantibodies. AIH type 1 (AIH-1) is characterised by smooth muscle and/or antinuclear autoantibodies (SMA/ANA) while anti-liver kidney microsomal (anti-LKM) or liver cytosol type 1 (anti-LC1) identified AIH type 2 (AIH-2). The conventional treatment is based on corticosteroids and azathioprine as first line therapy. The optimal duration is not clear definied, however it should be extended for at least five years due to the frequent relapses.

Aims of the study: The primary objective is to describe the prevalence and incidence of type 1 and 2 autoimmune hepatitis on a selected italian pediatric population. Secondary objectives are to analyze the clinical, biochemical and histopathological profiles at diagnosis and follow-up, type of treatment received, response to therapy and long-term follow-up.

Methods: The investigators conducted a retrospective and prospective cohort study on patients aged ≤ 18 years who the diagnosis of AIH 1 and 2 between 01/01/1989 and 31/12/2019 and were followed in three Italian pediatric centers.

Inclusion Criteria:

• Age ≤ 18 years at the time of diagnosis
• Diagnosis of autoimmune hepatitis type 1 or 2 according to the Mieli-Vergani score: a pre-treatment score> 15 or post-treatment> 17 indicates a definite diagnosis of Autoimmune Hepatitis; a pre-treatment score between 10 and 15 or post-treatment between 12 and 17 indicates a probable diagnosis.

Exclusion Criteria:

• Age> 18 years at the time of diagnosis
• Presence of other causes of liver disease
• Presence of overlap syndrome (hepatito-cholangitis)

The study population is represented by all the patients who presented the onset of Autoimmune hepatitis type 1 and type 2 from 01/01/1989 to 31/12/2019 and were followed at the Pediatric Hepatology Centers of Ferrara (Hospital Saint Anna of Cona), Naples (Federico II University Hospital) and Palermo (Mediterranean Institute for Transplants and Highly Specialized Therapies).