Restriction Fragment-Length Polymorphism Analysis

                          Restriction fragment-length polymorphism (RFLP) analysis is a powerful tool for the detection of known mutations and polymorphisms, which result in the loss or creation of a recognition site at which a particular restriction enzyme cuts. RFLPs are usually caused by mutation at a cutting site. 

                          DNA carrying the different allelic form will give different sizes of DNA fragments when digested with the appropriate restriction enzyme. 

                          The E4 allele on the APOE gene has been proven to be a major risk factor for late-onset familial and sporadic Alzheimer’s disease. DNA samples for APOE genotyping are prepared by PCR amplification and subsequent digestion with that HhaI restriction enzyme to yield constant fragments of 16, 18, and 35 base pairs and four typical polymorphic fragments of 48, 72, 83, and 91 base pairs, corresponding to alleles E1, E2, E3, and E4, respectively (30). 

                          The risk of developing Alzheimer’s disease for the individual having the E4/E4 genotype is about 90%, for the individual having the E3/E3 genotype, 20%; and for the individual having the E3/E4 genotype, 47%.