In functionally specialized PML bodies, such as in alternative lengthening of telomeres-associated PML nuclear bodies (APBs) and in immunodeficiency, centromeric instability, and facial dysmorphy (ICF) syndrome cells, the inner core of PML bodies contains chromatin, namely telomeric DNA in APBs or pericentric satellite heterochromatin of chromosome 1 in the giant PML bodies of ICF cells (38, 39). This evidence concerns the gene PML and Immunodeficiency.