Monosomy 21q: two cases of del(21q) and review of the literature

We report on two cases of partial monosomy 21 and review cases with a partial or an apparently full monosomy 21. In situ hybridization and/or molecular studies appear to be necessary tools to study imbalance in such a small chromosome and to perform further genotype-phenotype correlations. The segregation mode in cases with a translocation is adjacent 1, adjacent 2, and 3 :1 in about 1/4, 1/4, and 1/2 of the cases, respectively.