Infant leukaemias and cot deaths.

Infant leukaemias differ from childhood leukaemias in ways which suggest that when haemopoietic neoplasms combine fetal origins with rapid growth rates they prevent normal development of the reticuloendothelial system and thus cause the sudden death of apparently healthy babies (stillbirths or cot deaths). Cot deaths are commoner in boys and have a peak incidence during the first half of infancy-that is, during the period most affected by the switch from passive to active immunity. Babies born from July to December, who are intensively exposed to winter conditions form 1 to 5 months of age, are also at special risk. During this period more girls and more children born form January to June die of leukaemia; and within three months of birth an exceptionally high ratio of myeloid to lymphatic leukaemias has been replaced by a low ratio, which persists throughout childhood.