Abstract

Abnormally high levels of spontaneous and mitomycin C or diepoxybutane induced chromosome breakage were observed in lymphocytes from eight out of nine previously undescribed patients clinically diagnosed as having Fanconi's anaemia. The results suggest that the combination of spontaneous and induced chromosome breakage is a good aid in the differential diagnosis and we suggest that increased chromosome breakage is pathognomonic for this recessive disorder. It is, however, not possible to demonstrate consistently raised levels of induced chromosome breakage in obligate carriers. The patient who had normal levels of chromosome breakage had an atypical haematological picture and may suffer from a disease genetically different from Fanconi's anaemia.