PSEUDO-EXCLUSION FROM PATERNITY DUE TO MATERNAL UNIPARENTAL DISOMY-16

The investigation of a case of disputed paternity revealed indirect ex clusion of the alleged father in the haptoglobin system and in the DNA single-locus system D16S309/Hinf I (MS205). The paternity index for t he non-exclusion systems was > 10(6). Since both exclusion systems (HP and MS205) are located on chromosome 16, we investigated 10 microsnte llite loci covering this chromosome with 10-20 cM resolution. Analysis of the child's chromosome showed only alleles of maternal origin and lack of inheritance of paternal alleles for five informative loci. The markers close to die centromere of chromosome 16 were heterozygous, w hereas distal loci were either heterozygous or homozygous for maternal alleles. This is consistent with a maternal meiosis I nondisjunction of chromosome 16 leading to maternal uniparental heterodisomy. This ca se emphasizes that the opinion of non-paternity should be based on the absence of paternal alleles at genetic systems located on at least tw o different chromosomes.