On the pathogenesis of erythroleukaemia (H0493).

In erythroleukaemia megaloblastic changes can co-exist with leukaemic changes in the marrow. The cause of the disease must therefore be such as can cause megaloblastosis and at the same time be mutagenic. Failure of the thymidylate synthelase reaction, the commonest cause of megaloblastic anaemia, can be eliminated in erythroleukaemia because (a) the dU suppression test is normal in the disease and (b) failure of the thymidylate synthelase reaction is not mutagenic. The deamination of both cytosine and adenine is mutagenic but the deamination of cytosine alone is apparent and the nucleotide of cytosine is the prime mutagenic nucleotide in leukaemia and cancer. Megaloblastic changes can result from an inadequate supply of any one of the four nucleotides that enter into the composition of DNA and it is suggested that an inadequate supply of the mutagenic nucleotide of cytosine, possibly through impaired synthesis, could cause both the megaloblastic and leukaemic changes in erythroleukaemia.