Several studies have shown the importance of segmental deletions/duplications in the field of chromosome pathologies. Non allelic homologous recombination, NAHR, between chromosomes or sister chromatids, mediated by segmental duplications, is the foundation of frequent mechanisms for structural chromosome mutations such as micro-deletions, micro-duplications, translocations, inversions, and marker chromosomes. We analyzed three distinct genomic regions (22q11.2, 17p11.2, 16p11.2) and we discussed how the same chromosome region can be affected by deletion or by reciprocal duplication, respectively responsible for a syndrome or for a reciprocal counter-syndrome, with different phenotypic manifestation
