The examination of the ITI system in disputed paternities

106 paternity cases with a total of 114 putative fathers were examined in the inter-alpha-trypsin inhibitor (ITI) system. Analysis was performed by isoelectric focusing (IEF) of untreated sera on polyacrylamide gels. From 39 paternity exclusions, determined in other genetic systems, 7 were confirmed in the ITI system. In 75 expertises the alleged man was not excluded from fatherhood; in 68 cases the probability of paternity was W greater than 99.73%. The practical exclusion rate in the ITI system was therefore calculated to be 10.45%. The theoretical exclusion rate was determined to be 19.3%. In one paternity case the alleged father and the child showed inverse homozygosity in the ITI system, while the man was not excluded from fatherhood in 28 additional marker systems. The calculated probability of his paternity was 99.99%. The assumption of an incomplete expression of the ITI phenotypes in infants is supported by a significant deviation between the observed and expected ITI distributions at population equilibrium.