THE PREVALENCE OF SERUM ANTI-MITOCHONDRIAL ANTIBODY USING RECOMBINANT AUTOANTIGENS DEMONSTRATES UNEXPECTEDLY HIGH RATES AND MALE REPRESENTATION IN THE GENERAL POPULATION

Background: Current data on the epidemiology of primary biliary cirrhosis (PBC) are mostly descriptive and often weakened by their case-finding methods. In all studies, female patients with PBC outnumber men with a 10/1 ratio. Conversely, data on the prevalence of serum anti-mitochondrial antibody (AMA) come from selected series not representing the general population and have been carried out with indirect immunofluorescence methods. Materials and methods: We took advantage of a series of 2047 sera (1097 females, mean age 41 years) representative of a Northern Italian general population aged 21-65; these sera were collected in 1997 to study the prevalence of hepatitis virus infections in the region. We utilized a commercially available ELISA assay including all three major recombinant AMA autoantigens (BCOADC-E2, PDC-E2, OGDC-E2) covalently linked as well as an M2 preparation from beef heart mitochondria (Euroimmun, Luebeck, Germany); this assay has higher specificity and sensitivity compared to other methods. Serum tests of liver damage (AST, ALT) or cholestasis (GGT) were available for all samples, together with a detailed history of liver conditions known at the time of enrollment. Results: Out of 2047 sera, 16 were positive for AMA using our ELISA with recombinant antigens leading to a prevalence of 0.77% (95% CI 0.44-1.2%) and a male to female ratio of 1/2.2. In one case the diagnosis of PBC was known at the time of blood sampling while 4 patients had elevated ALT and GGT without evidence of viral infections. Conclusions: The use of recombinant AMA antigens suggests that AMA may be more prevalent than expected in the general population and among men. Available biochemical data suggest PBC in several cases but we are currently performing the follow-up visit of all AMA-positive subjects.