A FISH STUDY OF CHROMOSOME FUSION IN THE ICF SYNDROME - INVOLVEMENT OF PARACENTRIC HETEROCHROMATIN BUT NOT OF THE CENTROMERES THEMSELVES

We have used double fluorescence in situ hybridisation to study the in volvement of centromeres and paracentromeric heterochromatin in the ch romosome abnormalities seen in the ICF syndrome. To detect centromeres , we used a probe which labelled alphoid satellite DNA, and for the pa racentromeric heterochromatin a probe for classical satellite II. Our results show that it is always the paracentromeric heterochromatin of the relevant chromosomes that becomes decondensed in this syndrome and which fuses to produce multiradial configurations. However, the centr omeric regions, identified by their content of alphoid satellite DNA, appear never to become decondensed and always remain outside the regio ns of chromosome fusion in the multiradials.