BACKGROUND: The APOE*E4 allele of the gene for
apolipoprotein E (APOE) has been reported as a risk
factor for Alzheimer disease (AD) to varying degrees
in different ethnic groups.
OBJECTIVE: To
compare APOE*E4-AD epidemiological associations in
India and the United States in a cross-national
epidemiological study.
DESIGN: Case-control
design within 2 cohort studies, using standardized
cognitive screening and clinical evaluation to
identify AD and other dementias and polymerase chain
reaction to identify APOE genotyping.
PARTICIPANTS:
Rural community samples, aged 55 years or older
(n=4450) in Ballabgarh, India, and 70 years or older
(n=886) in the Monongahela Valley region of
southwestern Pennsylvania.
MAIN OUTCOME MEASURES:
Criteria of the National Institute of Neurological and
Communicative Disorders and Stroke-Alzheimer's Disease
and Related Disorders Association for probable and
possible AD and Clinical Dementia Rating (CDR) scale
for dementia staging.
RESULTS: Frequency of
APOE*E4 was significantly lower (P<.001) in Ballabgarh
vs the Monongahela Valley (0.07 vs 0.11). Frequency of
probable or possible AD, with CDR of at least 1.0, in
the Indian vs US samples, was as follows: aged 55 to
69 years, 0.1% (Indian sample only); aged 70 to 79
years, 0.7% vs 3.1%; aged 80 years or older, 4.0% vs
15.7%. Among those aged 70 years or older, adjusted
odds ratios (95% confidence interval) for AD among
carriers of APOE*E4 vs noncarriers were 3.4 (1.2-9.3)
and 2.3 (1.3-4.0) in the Indian and US samples,
respectively, and not significantly different between
cohorts (P=. 20).
CONCLUSION: This first report
of APOE*E4 and AD from the Indian subcontinent shows
very low prevalence of AD in Ballabgarh, India, but
association of APOE*E4 with AD at similar strength in
Indian and US samples.