BACKGROUND:: Acute fatty liver of pregnancy (AFLP) and the HELLP syndrome are the serious disorders during pregnancy. The aim of this study is to clarify the prevalence of common mutation in the alpha-subunit of the mitochondrial tri-functional protein: hydroxyacyl-CoA dehydrogenase (LCHAD)/3-ketoacyl-CoA thiolase/enoyl-CoA hydratase as well as to determine the correlation with the polymorphism of microsomal cytochrome P4502E1 (CYP2E1) in these conditions. METHODS:: Genomic DNA was extracted from three patients with AFLP/the HELLP syndrome. Exon 15 of LCHAD and 5'-flanking lesion of CYP2E1 was amplified by PCR and analyzed by RFLP with either of Pst I or the combination of Pst I and Rsa I, respectively. RESULTS:: None of the patients demonstrated the 1528G-C mutation in LCHAD gene. All the patients had homozygous wild-type genotype (c1/c1) in the 5'-flanking lesion of CYP2E1. CONCLUSIONS:: Although limited size of study, our observations suggest the low incidence rate of LCHAD common mutation among Japanese patients with AFLP/HELLP syndrome. Moreover, all of the patients had wild-type genotype of CYP2E1 in this study. Considering with the fact that the neonates from these patients has been in good health for at least 6 years from birth, there might be diverse etiologic factors of Japanese patients with AFLP/HELLP syndrome other than reported genetic mutations.