Abstract: Aim The distribution of N-acetylate phenotype in Chinese children and its relationship with Down's syndrome(DS) and Duchenne muscular dystrophy (DMD) was investigated. Methods Thirty-one subjects with Down's syndrome, 18 with Duchemne muscular dys-trophy and 154 healthy children were acetylate-phenotyped with caffeine as a probe drug,Urine samples were collected 2 hours after administration of 60~100 ml of 10 mg/100 ml caffeine-spiked coca cola and analyzed by high performance liquid chromatography (HPLC). The LgAFMU/1X of peak hight ratio was used to construct the frequence his-togram and probit plot and to assese slow and fast acetylator staus both in the healthy and the DS/DMD children. Results The range of lg AFMU/1X in healthy children was 0.45~1.86, and in those with DS and DMD was 0.15~1.56 and 0.15~0.38 respectively.The ratio of 0.25 [Ig(AFMU/1X)] was sellected as a cut-off and used to separate slow and fast acetylators. Slow acetylators in children with DS accounted for 41.9% (13/31) while with DMD 50% (9/18), significantly higher than 16.9% of healthy children (X² = 8.287, P<0.005 and X² = 11.367, P<0.005 respectively). Conclusions The acetylate status is polymorphic in Chinese healthy children. Slow acetylators of children with DS or DMD were more than those of healthy children. Age and sex had no significant influence to acetylate status.

Key words: N-acetylate phenotype, polymorphism, Down's syndrome, duchemne muscular dystrophy, caffeine