Further evidence of a silent plasminogen (PLG) allele in two paternity cases

Routine paternity testing has yielded two different cases of an apparent inverse homozygosity in the plasminogen (PLG) system. In one case, the child presented the phenotype PLG A and his putative father the type PLG B. The alleged father could not be excluded from the paternity in 25 additional blood group marker systems (biostatistical probability of paternity W greater than 99.75%). In the other case an incompatibility was found in a mother- child pair. Analysis of PLG was carried out by isoelectric focusing on neuraminidase-treated sera. In both cases the immunologic and functional detection showed weaker banding pattern of the affected PLG types. The assumption of a silent allele in the PLG system was confirmed by quantitative investigations. The allele frequency of PLG*Q0 in the South German population was estimated to be 0.0013. In the same sample the variant PLG A3 has been shown to be polymorphic.