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The objectives of this study were to evaluate all the non-synonymous single nucleotide polymorphisms (SNPs) in the DNase I and DNase I-like 3 (1L3) genes potentially implicated in autoimmune diseases as a functional SNP in terms of alteration of the activity levels. We examined the genotype distributions of the 32 and 20 non-synonymous SNPs in DNASE1 and DNASE1L3, respectively, in three ethnic groups, and the effect of these SNPs on the DNase activities. Among a total of 44 and 25 SNPs including those characterized in our previous studies [Yasuda et al., Int J Biochem Cell Biol 42 (2010) 1216-1225; Ueki et al. Electrophoresis 32 (2012) 1465-1472], only four and one, respectively, exhibited genetic heterozygosity in one or all of the ethnic groups examined. On the basis of alterations in the activity levels resulting from the corresponding amino acid substitutions, 11 activity-abolishing and 11 activity-reducing SNPs in DNASE1 and two activity-abolishing and five activity-reducing SNPs in DNASE1L3 were confirmed as a functional SNP. Phylogenetic analysis showed that all of the amino acid residues in activity-abolishing SNPs were completely or well conserved in animal DNase I and 1L3 proteins. Although almost all non-synonymous SNPs in both genes that affected the catalytic activity showed extremely low genetic heterogeneity, it seems plausible that a minor allele of 13 activity-abolishing SNPs producing a loss-of-function variant in both the DNase genes would be a direct genetic risk factor for autoimmune diseases. These findings may have clinical implications in relation to the prevalence of autoimmune diseases.

Members of the human DNase I family, DNase I-like 1 and 2 (DNases 1L1 and 1L2), with physiological role(s) other than those of DNase I, possess three and one non-synonymous SNPs in the genes, respectively. However, only limited population data are available, and the effect of these SNPs on the catalytic activity of the enzyme remains unknown. Genotyping of all the non-synonymous SNPs was performed in three ethnic groups including six different populations using the PCR-RFLP method newly developed. Asian and African groups including Japanese, Koreans, Ghanaians and Ovambos were typed as a single genotype at each SNP, but polymorphism at only SNP V122I in DNase 1L1 was found in Caucasian groups including Germans and Turks; thus a Caucasian-specific allele was identified. The DNase 1L1 and 1L2 genes show relatively low genetic diversity with regard to these non-synonymous SNPs. The level of activity derived from the V122I, Q170H and D227A substituted DNase 1L1 corresponding to SNPs was similar to that of the wild-type, whereas replacement of the Asp residue at position 197 in the DNase 1L2 protein with Ala, corresponding to SNP D197A, reduced its activity greatly. Thus, SNP V122I in DNase 1L1 exhibiting polymorphism exerts no effect on the catalytic activity, and furthermore SNP D197A in DNase 1L2, affecting its catalytic activity, shows no polymorphism. These findings permit us to postulate that the non-synonymous SNPs identified in the DNase 1L1 and 1L2 genes may exert no influence on the activity levels of DNases 1L1 and 1L2 in human populations.

We devised a simple DNA extraction procedure suitable for STR typing of urine sample. Use of a commercially available DNA/RNA extraction kit equipped with a silica-gel-based membrane made it possible to omit the recovery of urinary nucleated cells by sedimentation before the extraction. Successful genotyping of the TH01, HumTPO and multiplex STRs was achieved using aliquots of urine as small as 100 µL. Furthermore, application of this DNA extraction procedure to frozen urine samples provided STR allele results comparable to results obtained from fresh samples. Therefore, this extraction procedure is considered to be effective for STR typing of urine samples in both the frozen and aqueous state. Furthermore, addition of sodium azide to fresh urine samples prolonged their storage duration even at room temperature.