DISSOCIATED 24-HOUR PATTERNS OF SOMATOTROPIN AND PROLACTIN IN FATAL FAMILIAL INSOMNIA

To assess the changes in the 24-hour profiles of serum somatotropin an d prolactin levels during total disruption of the sleep/wake cycle sus tained over several months, we studied 2 subjects affected by fatal fa milial insomnia, a rare disease characterized by selective thalamic de generation that causes chronic sleep loss. Under standardized conditio ns and polysomnographic control, the patients underwent repeated 24-ho ur study sessions covering the entire clinical course of the disease. Hormones were assayed at 30-min intervals. Four healthy volunteers wer e used as controls. A sleep/wake cycle was always absent in fatal fami lial insomnia. Serum somatotropin and prolactin concentrations never e xceeded the normal range of variation. The nocturnal elevation of soma totropin disappeared simultaneously with sleep loss, whereas a signifi cant 24-hour component of variations in serum prolactin levels was pre sent for months after total disruption of the sleep/wake cycle, with n ormally placed nocturnal acrophases. Complete obliteration of the 24-h our component was achieved for prolactin only in the advanced stages, through a progressive decrease in 24-hour amplitude of variation. Sele ctive and progressive degeneration of the mediodorsal and anterior ven tral nuclei of the thalamus causes an early obliteration of the 24-hou r rhythm of somatotropin and a later disappearance of circadian prolac tin rhythmicity. The persistence of a significant circadian rhythm for months after total disruption of the sleep/wake cycle indicates that prolactin rhythmicity is not exclusively sleep-entrained.