The assay allows the discrimination between six possible heterozygous or homozygous genotypes
E2/2, E2/3, E2/4, E3/3, E3/4, E4/4.
Apolipoprotein E (apo E) plays a key role in lipid metabolism by mediating the interaction of lipoproteins with their receptors. The protein exists in three major isoforms (E2, E3, E4) due to two polymorphic sites (C versus T at codons 112 and 158) within the apo E gene located on chromosome 19q13.2. There is strong evidence that the different apo E variants play a causative role both for cardiovascular disease (CVD) and Alzheimer ´s Disease (AD). Compared to the most frequent variant apo E3 (~ 77%), the apo E2 isoform (~ 8%) is usually associated with decreased and the apo E4 isoform (~ 15%) with increased serum total and LDL cholesterol levels. It has been suggested that up to 10% of the phenotypic variance of serum cholesterol level is attributable to apo E. The apo E4 isoform has been described as a risk factor for atherosclerosis and premature coronary and peripheral vascular disease. On the other hand, homozygosity for the apo E2 variant seems to predispose individuals to type III hyperlipoproteinemia. The apo E4 isoform is also a well established risk factor for lateonset familial and sporadic forms of AD. Conversely, the E2 isoform is underrepresented among AD patients and seems to confer protection against the disease.