The paraoxonase family in humans includes the PON1, PON2, and PON3 genes. These genes are located on the long arm of chromosome 7 and are structurally similar .Between the nucleotide sequences of these three genes is about 70% and between their amino acid    sequences is about 60% compatibility. The three have 9 exons, which in the case of PON1 exists an addition code in position 106 (lysine) in exon 4, which is not present in other isoenzymes.  
PON3 mRNA is mainly expressed in the liver and less in the kidney. PON1 mRNA is expressed in the liver, while PON2 enzyme mRNA is expressed in different tissues.                                                                                 
Unlike paraoxonase 1, paraoxonase 2 and 3, have more limited paraoxonase and aryl esterase activity. They mostly have an antioxidant role that decreases intracellular oxidation. Paraoxonase 2 is an intracellular enzyme.It decreases Oxidation of LDL in cells. Paraoxonase 3 is associated with serum HDL to a lesser extent than paraoxonase 1. Measuring the concentration of these enzymes in various diseases such as arthritis Rheumatoid arthritis, hyperthyroidism, autism, alzheimerchr('39')s, uremia, atherosclerosis, coronary artery disease, diabetes, Smoking, hyperlipidemia, liver and kidney disease have diagnostic value.