Familial associations of Alzheimer disease and essential tremor with Parkinson disease.
BACKGROUND
We constructed a cohort of first-degree relatives of participants in a population-based case-control study of Parkinson disease (PD) and compared the occurrence of Alzheimer disease (AD) and essential tremor (ET) in relatives of PD cases and controls.


METHODS
We relied on proband interviews to assess family history in 372 probands with incident PD confirmed by a movement disorder specialist and 404 controls from three rural California counties.


RESULTS
Overall, for the 2980 first-degree relatives of PD cases, the risk of AD was not increased compared with the 2981 relatives of controls. But relatives of younger onset PD cases (<or=60 years of age) were three times more likely to have received an AD diagnosis [hazard ratios (HR): 2.86; 95%CI: 1.44, 5.71]. Our data also suggest that some relatives of PD probands might be at a slightly increased risk of receiving an ET diagnosis, especially relatives of tremor dominant cases (HR: 1.69; 95%CI 0.99, 2.88), younger onset cases (HR: 2.03; 95%CI 0.93, 4.44), and male relatives (HR: 2.31; 95%CI 1.13, 4.73). In addition, fathers of cases were almost 15 years younger than fathers of controls when diagnosed with ET. Results were stable in sensitivity analyses.


CONCLUSIONS
Our study suggests a familial susceptibility to AD amongst first-degree relatives of younger onset PD cases.
Costello
S
S
University of California, Los Angeles, Schools of Public Health and Medicine, Los Angeles, CA, USA. sadie@berkeley.edu
Bordelon
Y
Y
Bronstein
J
J
Ritz
B
B
D017668:Age of Onset; D000368:Aged; D000544:Alzheimer Disease / Q000453:epidemiology* / Q000235:genetics; D016022:Case-Control Studies; D015331:Cohort Studies; D020329:Essential Tremor / Q000453:epidemiology* / Q000235:genetics; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000453:epidemiology* / Q000235:genetics; D010375:Pedigree; D012307:Risk Factors