PON1 is a polymorphic enzyme closely associated with high-density lipoproteins. It is located on chromosome 7 along with 2 other paraoxanase genes, PON2 and PON3. It is a 355 amino acid, 43 kDa glycoprotein produced in the liver and secreted into the bloodstream. Gene polymorphisms occur in both coding and non-coding regions. Two major polymorphisms in the coding region are L55M and Q192R. Q192R polymorphisms result in three major functional phenotypes Q/Q, Q/R and RR. PON1 hydrolyses organophosphates and prevents the oxidation of low-density lipoproteins. It may inhibit the progression of atherosclerosis by inhibition of LDL oxidation. Levels of PON1 in serum vary among individuals and are decreased in chronic renal failure, liver cirrhosis, diabetes, peripheral neuropathy, and familial hypercholesterolemia.