The recent report by Olson et a1 [1983] on the use of chromosome analysis in cases of disputed paternity is of scientific and intellectual interest. The set of genetic systems utilized at the Paternity Testing Laboratory, Oregon Health Sciences University, is laudable in that it includes a rational, highly efficient, and cost-effective group of genetic markers for paternity testing with an exclusion chance of over 98% for falsely accused men. The exclusion chance of 98% for the 21 systems utilized is an average value for all cases and can be used in advance of testing to describe the efficiency of the extent of testing by the laboratory. After the phenotypes have been defined, the exclusion chance can be calculated for the specific mother-child combination [Morris, 19831. In the case reported, the exclusion chance is relatively low (not close to 98%) because the child has some very common phenotypes eg, 0, R,r, Fy(a -b +), Jk(a +b+), etc.
As the authors indicate, when the paternity index is low (and/or when the specific exclusion chance is low), in spite of such a testing protocol, there is a need to test for additional genetic markers.
Although chromosome analysis as presented in the paper by the authors, is interesting and useful, the HLA system, rather than chromosome analysis, would appear to be the next logical system to examine for two reasons: (1) It offers a very high exclusion chance for nonfathers of over 90% [Houtz et al, 1981; Singh et al, 19821 in contrast to the 72-74% cited by the authors for chromosome analysis. (2) In most areas of the country, HLA typing is less expensive than chromosome analysis.
Both methods would require the trio to return for restudy. It would be of interest to know the HLA phenotypes and the racial origin of the trio reported in the paper.