we analysed data from the czech part of the hapiee project ( peasey et al . the study recruited over 8000 caucasian men and women aged 4569 years at baseline ( 20022005 ) , randomly sampled from population registers of seven czech towns . dna was extracted from venous blood samples and apoe genotypes were determined using the conventional pcr - rflp method ( hixson & vernier , 1990 ) . two criteria were adopted to define hand dominance , both using data collected during the re - examination of the cohort in 20062008 ( total of 5362 participants ) . second , we used grip strength data and classified as left - handed those who recorded higher grip strength on their left hand on both successive tests . both hand dominance and apoe genotype were available for 4438 participants ( 2022 males and 2416 females ) , mean age 58.0 ( sd 7.1 ) years . differences in the proportion of left - handed individuals between apoe subgroups , both in the full sample and when stratified by age and sex , were assessed by a chi - square test . in addition we tested the association between left - handedness and the presence of the apoe2 allele vs either apoe33 or 43/44 , using logistic regression . we also assessed the association separately by 5-year age group , and we tested for potential interaction between age group and apoe genotype . all analyses were conducted using the stata version 12 statistical software ( station college , tx , usa ) . the study was approved by the local ethics committees at both czech national institute of public health and at university college london . a total of 217 ( 4.9% ) individuals reported having a dominant left hand for writing and 543 ( 12.2% ) persons had consistently higher grip strength on their left hand . these two measures were strongly correlated ; individuals with higher left hand grip strength were five times more likely to be self - reported left - handers ( odds ratio 5.2 , 95% confidence interval 4.06.7 , p < .0001 ) . the frequency of the most common apoe3 allele was 81.1% , followed by the apoe4 allele ( 11.3% ) , and the least common was the apoe2 allele ( 7.5% ) . the distribution of left - handers based on either self - report or grip strength did not differ between carriers of different apoe genotypes ; the p - values were 0.828 (  2.1 , 5 df ) and 0.557 (  3.9 , 5 df ) ( table 1 ) . similarly , there were no statistically significant differences when carriers of apoe2e2 and apoe2e3 were combined , and compared with apoe3e3 homozygotes and with apoe4 ( apoe4e3 and apoe4e4 ) carriers , with no odds ratio being anywhere close of statistical significance ( table 2 ) . distribution of left - handers among the different apoe genotypes age - sex - adjusted and age - specific odds ratios of left - handedness by presence of apoe2 allele , with confidence intervals and p - values . left - handedness was the dependent variables coded as 0 ( non - left - handed ) and 1 ( left - handed ) ; the presence of apoe2 allele was coded as 0 ( no apoe2 allele present ) and 1 ( at least one apoe2 allele present ) . adjusted for age and sex further analyses , stratified by 5-year age group , did not reveal any significant association between left - handedness and apoe genotype in any age group , nor any interactions between apoe and age group ( table 2 ) . similar analyses , stratified for sex , also produced negative results ( table 2 ) . while many studies have suggested a genetic contribution to handedness ( see annet , 1994 ) , very few studies investigated specific genetic markers in relation to left-/right - handedness ( scerri et al . this study , a study of children , did find an association between apoe and left handedness ( bloss et al . , 2010 ) . our study , much larger than the previous investigation but in adults , did not find any association between apoe genotype and hand dominance . the apoe genotype frequencies in our study were similar to the frequencies detected in neighbouring populations ( bazrgar et al . 2008 ; gerdes , klausen , sihn , & faergeman , 1992 ) ; they also did not differ significantly from the study by bloss et al . the genotype frequencies were also similar to a study conducted in neighbouring slavonic / polish population in which the apoe4 allele was associated with elevated risk of alzheimer disease ( klimkowicz - mrowiec et al . , 2010 ) . there are two main limitations of our study : the measurement of handedness and the restricted age range of the examined individuals . both these factors limited our ability to analyse life - long handedness and possible redirection of handedness in childhood . hand preference is more a continuous rather than binary trait , and ambidexterity may be more common than strict left - handedness ( llaurens et al . , the assessment of handedness in our study was based on subjective self - report and on measurement of grip strength , not allowing to us to detect the potential ambidextrous individuals . none of our two outcome classifications is ideal , especially because the age groups included in our study might have been forced to use their right hand when they were children . this fact may also explain the discrepancy between self - report and grip strength results , although in both methods the proportions of left - handers were reasonably close to the expected range of 5 to 10% ( llaurens et al . , 2009 ) . on the other hand one might argue that the degree of enforcement might have differed between sexes or between birth cohorts ; the absence of any confounding or effect modification by age or sex contradicts the presence of a major bias . the observations that the proportion of left - handed persons based on grip strength was close to prevalence of 12% reported in an earlier study in the czech population ( dvorakova , & zvolsky , 1989 ) , and the expected higher prevalence in males than females , further suggest that the grip strength based measure may be the more reliable of the two measures . our study had sufficient power to detect relatively modest differences in the prevalence of left - handedness between apoe2 carriers and carriers of others genotypes , and the three - fold difference reported by bloss et al . however , we can not completely exclude the possibility that small differences exist in left - handedness and apoe genotypes . given the low prevalence of apoe2e2 and apoe4e4 homozygosity ( less than 1% ) , a much larger study would be needed to demonstrate such a small effect for these rare genotypes . notwithstanding these limitations , there was no suggestion of an association between apoe genotype and left - handedness . ( in press ) . we therefore conclude that common polymorphism within the apoe gene is likely not a major genetic determinant of left - handedness in adults .
an association between apoe genotype and left - handedness has been previously reported . 
 we examined whether such association exists in a population sample of 4438 unrelated caucasian adults aged 4569 years ( 2022 males and 2416 females ) . 
 left - handedness was based on self - reported left - hand dominance for writing ( prevalence 4.9% ) and on consistently higher left - hand grip strength in two repeated measurements ( prevalence 12.2% ) . 
 individuals with higher left hand grip strength were seven times more likely to be self - reported left handers ( p < .0001 , 2 159.7,2 df ) . 
 there were no differences in the proportion of self - reported left - handedness ( p = .828 , 2 2.1 , 5df ) or higher grip strength in left hand ( p = .557 , 2 3.9 , 5 df ) between apoe genotypes . 
 the lack of association was similar in both genders and did not differ by age group . 
 the results suggest that left - handedness in adults is not related to apoe genotype .