Episodic memory impairment in Huntington's disease: a meta-analysis.

Memory dysfunction is an important feature in the clinical presentation of Huntington's disease (HD) and may precede the onset of motor symptoms. Although several studies have contributed to the quantitative and qualitative description of memory impairments in HD, the characterization of episodic memory impairments has varied considerably. Whereas most studies report significant impairments on free recall tests, performance on recognition tests has been considerably more variable, ranging from normal to markedly deficient. This absence of a well-established recognition memory deficit has led some investigators to attribute the memory deficits in HD to a retrieval-based episodic memory impairment. We felt that a quantitative review of the literature was needed to better characterize these episodic memory impairments. We conducted a meta-analysis to assess the magnitude of the recognition memory deficit in HD and to examine it in relation to the known deficit in recall. Memory data were provided by 544 symptomatic HD patients, 224 presymptomatic gene-carriers, and 963 control subjects. The overall group comparison between symptomatic patients and controls yielded effect sizes of d=1.95 for free recall and d=1.73 for recognition. We split the symptomatic group into two subgroups based on their mental status (mild and moderate/severe dementia) and both showed significant deficits in recall and recognition memory, though recall was more impaired than recognition in the mild dementia subgroup. Only slight memory impairment was observed in the presymptomatic subjects. The results show that deficits in recognition memory must be accounted for in future models of memory impairment in HD.