In turn, one of the identified intragenic SNP-CpGs represents functional polymorphism, introducing non-conservative amino acid substitution in the region of the protein domain which would impair the enzymatic activity of RNASEL. It was found that impairment of RNASEL in old age results in increased susceptibility to viral infections in model animals (Pfeifer et al. 1993). This evidence concerns the gene RNASEL and viral infectious disease.