One of the likely contributing factors to these sleep disturbances is an inverse circadian pattern of the sleep-promoting hormone, melatonin. In SMS, plasma melatonin is high during the day and low at night, which is opposite the normal pattern. The underlying reason for this regular daytime melatonin secretory pattern is unknown. To our knowledge this pattern is distinctive to persons with SMS and not found elsewhere. SMS therefore offers a unique human syndrome for the study of melatonin function. At the present time, there is no effective treatment for sleep disturbances in SMS. Moreover, there are currently no controlled treatment trials underway in the U.S. with the specific goal of correcting the disturbed sleep pattern observed in this disease.