Functional Single Nucleotide Polymorphisms (SNPs) in the Genes Encoding the Human Deoxyribonuclease (DNase) Family Potentially Relevant to Autoimmunity

<p><b>Objective</b>: To continue our previous investigations, we have extensively investigated the function of the 61, 41, and 35 non-synonymous single nucleotide polymorphisms (SNPs) in the human genes encoding <i>DNASE1, DNASE1L3</i>, and <i>DNASE2</i>, respectively, potentially relevant to autoimmune diseases.</p> <p><b>Methods</b>: The site-directed mutagenesis was employed to amino acid–substituted constructs corresponding to each SNP. The COS-7 cells were transfected with each vector and DNase activity was assayed by the single radial enzyme diffusion method. By using PolyPhen-2, changes in the DNase function of each non-synonymous SNP were predicted. Genotyping of all the non-synonymous SNPs was performed in 14 different populations including 3 ethnic groups using the polymerase chain reaction followed by the restriction fragment length polymorphism method.</p> <p><b>Results</b>: Expression analysis demonstrated these SNPs to be classified into four categories with regard to the effect on DNase activity: SNPs not affecting the activity level, ones reducing it, ones abolishing it, and ones elevating it. In particular, 9, 5, and 4 SNPs producing a loss-of-function variant of the enzymes in <i>DNASE1, DNASE1L3</i>, and <i>DNASE2</i>, respectively, were confirmed. SNPs producing DNase loss of function can be estimated by PolyPhen-2 to be “probably damaging” with a high accuracy of prediction. Almost all of these functional SNPs producing a loss of function or substantially low activity-harboring forms exhibited a mono-allelic distribution in all of the populations.</p> <p><b>Conclusion</b>: A minor allele of functional SNPs, despite the remarkably low genetic heterogeneity of the SNPs, might be a genetic risk factor for autoimmune diseases.