Paraoxonase 1 192 and 55 polymorphisms in osteosarcoma. Paraoxonase is an HDL-associated enzyme that plays a preventive role against oxidative stres. Previous studies suggested that involved an amino acid substitution at position 192 gives rise to two alloenzymes with a low activity (Q allele) and a high activity (R allele) towards paraoxon. There also exists a second polymorphism of the human PON1 gene affecting amino acid 55, giving rise to a leucine (L-allele) substitution for methionine (M-allele). PON1 gene polymorphisms were studied in 50 patients with osteosarcoma and 50 healthy controls. Paraoxonase genotypes were determined by PCR-RFLP. We found a reduction in the frequency of PON1 192 R allele in patients (P=0.015). Besides, PON1 192 wild type QQ genotype (P=0.015) and PON1 55 wild type L allele (P=0.001) were higher in patients compared to healthy controls. PON1 192 QQ genotype was associated with osteosarcoma in multivariate logistic regression analysis. Our findings have suggested that PON1 192 wild type genotypes may be associated with a risk of developing osteosarcoma.