sentences:  The hypothesis has held true in the case of putative causal variants in apolipoprotein E, including "APOE" ε4, associated with Alzheimer's disease.IL23R has been found to be associated with Crohn's disease; the at-risk allele has a frequency 93% in the general population .One common form of variation across human genomes is called a single nucleotide polymorphism (SNP).