The common disease-common variant (often abbreviated CD-CV) hypothesis predicts that common disease-causing alleles, or variants, will be found in all human populations which manifest a given disease.Common variants (not necessarily disease-causing) are known to exist in coding and regulatory sequences of genes.s indicated by the name, SNPs are single base changes in the DNA. SNP variants tend to be common in different human populations. These polymorphisms have been valuable as genomic signposts, or markers, in the search for common variants that influence susceptibility to common diseases.