Apolipoprotein E epsilon4 and impaired episodic memory in community-dwelling elderly people: a marked sex difference. The Hordaland Health Study.

BACKGROUND: Among elderly people without dementia, the apolipoprotein E epsilon4 allele (APOE4) has been associated with cognitive deficit, particularly in episodic memory, but few reports are available on whether this association differs by sex. METHODS: In a community-dwelling Norwegian cohort of 2181 elderly people (55% women), aged 70-74 years, episodic memory was examined in relation to sex and APOE4 zygosity, with the Kendrick Object Learning Test (KOLT). RESULTS: Possession of at least one APOE4 allele had a modest, detrimental effect on episodic memory in women, whereas in men, heterozygotes were unaffected and homozygotes had markedly lower scores across the distribution of KOLT scores. This sex difference was found consistently in all analyses: on comparing means and medians, examining trends across quintiles, and studying the distribution of scores and the risk of cognitive impairment. Results were broadly similar when adjusted for known determinants of cognition and also when severely impaired participants were excluded. The adjusted odds ratio (OR) of cognitive impairment in women was shown to be 1.8 (95% confidence interval (CI): 1.1 to 2.8) for heterozygotes and 1.1 (0.3 to 3.7) for homozygotes; the adjusted OR in men was observed to be 1.1 (0.6 to 2.1) for heterozygotes and 10.7 (4.7 to 24) for homozygotes. CONCLUSIONS: Although the harmful effect of APOE4 on episodic memory was modest in women, the risk was found to occur in about 30%. APOE4 was observed to have a dramatic effect on episodic memory in men, but only in homozygotes, who comprised about 3% of men: the whole male homozygous group showed a marked shift to lower memory scores.