Robertsonian translocation t dic (14p;22p) with regular trisomy 21: a possible interchromosomal effect?

Robertsonian translocations occur in about 2.5% of Down syndrome. We report here a Down syndrome with karyotype, 46,XX,-14,-22,+der t dic(14p;22p)pat, +21. Proband's father, two sisters, and a brother are phenotypically normal, heterozygous carriers for dicentric t(14;22). This is the only case of a translocation t(14;22) with regular trisomy 21 in our series of 600 Down syndrome cases investigated. The prevalence of balanced Robertsonian translocations in parents of Down syndrome might be higher if all the parents of trisomy 21 individuals were routinely investigated. The case is of interest in understanding the possibility of interchromosomal effect in the etiology of non-disjunction in Down syndrome.