The relationship between cortisol and verbal memory in the early stages of Huntington's disease

Hypothalamic pituitary adrenal (HPA) axis hyperactivity has been linked to learning and memory difficulties in a range of neurodegenerative and neuropsychiatric conditions. In Huntington's disease (HD), both declines in learning and memory and HPA axis dysfunction are present early in the disease. However, the relationship between specific learning and memory deficits and HPA axis functioning in HD has not been examined. The aim of this study was to investigate cortisol levels in relation to verbal learning and memory in pre-diagnosed (pre-HD) participants and patients at the early stages of diagnosed HD (early-HD). Cortisol concentration was assayed in saliva samples from 57 participants (17 early-HD, 20 pre-HD, and 20 controls) at four time-points across a 24-h period. Verbal memory was assessed using the California Verbal Learning Test-Second Edition (CVLT-II). We focused statistical analyses on the late evening cortisol concentration, and examined cortisol levels and verbal memory function in relation to diagnostic group (control, pre-HD, early-HD), and in a separate set of analyses combining pre-HD and early-HD (and excluding controls) we also examined cortisol and verbal memory performance in relation to the severity of HD-related motor signs. Of these two classification approaches, HD motor sign severity was more strongly associated with high evening cortisol levels and both reduced information encoding and memory retrieval. Separately, there was also a trend of higher cortisol levels in pre-HD. The findings suggest hypercortisolism and the underlying pathological changes may begin many years before a clinical diagnosis is made, but the memory decline associated with HPA axis disturbance may only become detectable once motor signs become pronounced.