Small accessory chromosomes (SAC) and their genotype--phenotype correlation

A total of 39 carriers of small accessory chromosomes (SAC) was found among 32,930 patients karyotyped in Division of Human Genetics, Catholic University, Leuven, Belgium, in the years 1966-1981. In majority of SAC carriers the origin of extra-chromosome material remained unknown (21 out of 29 index patients), even when applying different banding techniques. The only common feature of all described SAC seems to be the presence of C-banded heterochromatin. The genotype-phenotype correlation in SAC carriers has been discussed.