Inter-alpha-trypsin inhibitor (ITI): a useful genetic system in paternity testing. Evidence for polymorphic occurrence of ITI*3 and existence of a new allele, ITI*4.

The genetic polymorphism of human inter-alpha-trypsin inhibitor (ITI) has been investigated in sialidase-treated samples by isoelectric focusing on polyacrylamide gels with a pH range 3.5-9.5 followed by passive blotting with enzyme immunoassay. In 400 blood donors from western Japan, 8 simplified band patterns were observed, 6 of which could be explained by the previously described 3 polymorphic alleles, ITI*1, ITI*2, and ITI*3. The others were products of a new and rare fourth allele designated ITI*4, whose expression is also consistent with autosomal codominant inheritance. The frequency of these alleles was 0.440, 0.526, 0.030 and 0.004, respectively. The theoretical exclusion rate for putative fathers in paternity cases was calculated to be 0.228. The ITI system is a useful genetic marker for forensic hemogenetics in Japanese and in Europeans.