[Epidemiological study of selective IgA deficiency among 6 nationalities in China].

The frequency of selective IgA deficiency (SIgAD) was determined in 33,171 Chinese distributed in six nationalities by Ouchterlony's double diffusion with 5 mg/dl as the limit of detection. Those who were found IgA-deficient were retested by single radial diffusion technique. Gel diffusion analysis of sera revealed apparent lack of IgA in 8 samples, all with normal levels of IgG and IgM (age-matched). The incidence was 0.024% (1:4,100). The incidences among the six nationalities were Han 1:2,600, Hui 1:5,000, Mongolia 1:2,700, Tujia 1:4,300, Zhuang 0:5,300, and Bai 1:4,800. All of the individuals, who had low levels of IgA or no IgA detectable, were below 16 years of age. Of these, 2 sera were autoantibody (anti-smooth muscle antibody) positive Delayed hypersensitivity skin tests were negative in one individual. The chief clinical manifestations were those of respiratory tract infections, of which about 50% were in subclinical state.