Multiple small accessory marker chromosomes from different centromeric origin in a moderately mentally retarded male

The occurrence of more than two small accessory chromosomes (SACs) in a sin gle individual is extremely rare. Here, we characterize six SACs found in t he cells of two different tissues of a moderately mentally retarded male. M icrodissection combined with regular FISH demonstrates that the SACs are ri ng chromosomes derived from the centromeres of different chromosomes. The S ACs are often associated with the centromeres of other chromosomes. Immunof luorescence with an anti-CENP-C antibody demonstrates that the SACs contain an active centromere. A possible mechanism by which the SACs originated an d their clinical relevance are discussed.