Down's syndrome with an atypical G-G translocation derived from familial pericentric inversion in one chromosome of the G group.

In a young male with Fanconi's anaemia, 10% of cells in a direct bone marrow preparation had chromosome abnormalities. Breaks involving primarily groups B and C members constituted the most frequent changes encountered, while 2 cells had either a dicentric or a ring chromosome. Smears from the same aspirate showed anaphase bridges in 3oo of mitoses. It is suggested that in this disease chromosome breakage is a process in vivo, and that its occurrence in bone marrow cells possibly contributes to their progressive elimination and ultimate depletion.