network, family, academic or unknown type, based on the Adolescent Perceived Event Scale of Compas et al. [21] (personal communication: B. Compas, Vanderbilt University). Illness onset was defined as the month and year when the first symptom related to myositis developed. A paediatric rheumatologist (L.G.R. or G.M.) reviewed available medical records for 81% of the patients in order to confirm the reported exposures, as well as the diagnostic and clinical material contained in the questionnaire. Patient sera were tested for myositis autoantibodies by validated methods [22, 23] . For anti-p155/140 and anti-MJ autoantibodies, serum samples were screened by immunoprecipitation (IP), and this was confirmed by IP blotting [5, 24] . Sera were considered positive if they blotted the antigen in immunoprecipitates prepared using reference serum (direct) or if reference serum blotted the antigen in immunoprecipitates prepared using patient serum (reverse). Since some IP-positive sera do not react by immunoblotting, reverse IP blotting was used for most sera [5] .