A paternity case with three genetic incompatibilities between father and child due to maternal uniparental disomy 21 and a mutation at the Y chromosome.

A parentage case is described that revealed a potentially erroneous exclusion from paternity in three systems, two on chromosome 21 and one on chromosome Y. Follow-up tests, especially of chromosome 21, were subsequently performed. Actually, the child's chromosome 21 showed alleles of maternal but not of paternal origin being consistent with a maternal uniparental disomy of chromosome 21.