The influence of calendar month, day length (photoperiod), and globar solar radiation (GSR) on onset of infantile spasms was reviewed retrospectively using records of 76 infants at the Hospital for Sick Children, University of Toronto, Ontario, Canada. Onset frequency increased as days were shorter, with a 2.2-fold higher frequency in December/January, months with a short photoperiod and low GSR, compared to June/July. Environmental photoperiodic factors (zeitgebers) may have a role in onset of infantile spasms. 
COMMENT. The frequency of infantile spasm onset is highest in the fall and winter, during months with low globar solar radiation and short photoperiods. Possible causal factors suggested include seasonal variations in seizure threshold or ACTH release. Viral infections might also be a seasonal etiology.
Several factors may modify the threshold to seizures in animals and man, and seasonal variations have received little attention. Boldrey EE and Millichap JG, in a laboratory study and report of barometric pressure and seizures , refer to WF Petersen’s extensive treatise concerning effects of weather on disease and the relation between meteorological disturbances and onset and severity of epilepsy (1934). Also,. Tille D had observed a higher incidence of febrile convulsions related to cold weather fronts (1950).