Causes of association - 1: Direct effect of polymorphism on risk
If the polymorphism being used as a marker actually occurs within a gene and alters the amino acid sequence being coded, or affects transcription, then different alleles may lead to differences in the nature or quantity of the gene product. This may then affect susceptibility to the disease.
Subjects with one or two copies of the D allele have an abnormal form of the protein resulting in increased risk of developing disease.
