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Handedness in Blood Donors: No Association with Blood Group or Twinning
NOTE HANDEDNESS IN BLOOD DONORS: NO ASSOCIATION WITH BLOOD GROUP OR TWINNING R. Morley! and E.A. Caffrey2 eMedical Research Council Dunn Nutrition Unit, Cambridge; 2East Anglian Blood Transfusion Centre, Cambridge)
INTRODUCTION
There is evidence for an inherited component in the determination of handedness (McManus, 1991) but the nature and genetic location of this is uncertain. In a cohort of 766 children aged 7.5 to 8 years born weighing under 1850 g there was a trend to more left handedness for writing in children with blood group B or AB, compared with those from other blood groups (unpublished data on children froma multicentre study; Morley, Cole, Powell et aI., 1988). Although it was likely that this was a chance finding, it would be of considerable interst if confirmed in a larger population. We therefore studied a large cohort of blood donors to investigate whether there is any association between ABO blood group and handedness. Although this was our primary objective we felt that there were a number of other important issues relating to handedness which could be addressed by this study; namely the reported associations of handedness with twinning, gender and age. It has been widely reported that left handedness is more common in twins, though this has not been a consistent finding. The evidence for the influence of twinning on handedness has been reviewed by McManus (1980) and Bishop (1990). In the cohort studied by Morley et al. (1988) there was a strong trend to more left handedness among twins than in other children born preterm and it is of interest whether this same trend applies to twins in general. Right handedness is widely reported to be slightly less common in males (Annett, 1985) and more common with increasing age (Ellis, Ellis and Marshall, 1988). We have therefore also investigated the influence of twinning, gender and age on handedness in the large blood donor group. MATERIALS AND METHODS
Questionnaires were taken to blood donor sessions organised by the East Anglian Blood Transfusion Centre and donors were asked to fill one in while resting after giving blood. Donors cannot give blood at less than 3 monthly intervals and all forms were completed within a month; no subject, therefore, could have been included twice. The questions are shown in Table I. In order to detect, with 90% power, a 5% difference in left handedness between subjects with blood Groups B or AB versus other groups we calculated that 2700 subjects would be required. To allow for wastage 4000 forms were distributed among the four regional blood collection teams. Statistical analyses, for comparing proportions between groups, were by chi-squared.
RESULTS
Altogether 3815 forms were filled in and the number of subjects completing each item is shown in Table I. Median age was 39 years (25th percentile 30 and 75th 47 years). Of the 3814 subjects reporting gender 1821 (47.7%) were males and 1993 (52.3%) females; Cortex, (1994) 30, 707-710
R. Morley and E.A. Caffrey
708
TABLE [
Responses to Questionnaire
I 2 3 4 5 6
7 8 9 10
Total number completing item
Right n (%)
Left n (%)
Either n (%)
3815 3814 3796 3754 3815
3360 (88.1)
445 (11.7)
10 (0.3)
3813
3325 (87.2)
418 (11.0)
70 (1.8)
3815
3330 (87.3)
442 (11.6)
43 (1.1)
3807
3204 (84.2)
437 (11.5)
166 (4.4)
3813
3100 (81.3)
380 (10.0)
333 (8.7)
Age in years Are you male or female? Do you, or did you have a twin? What is your blood group? Which hand do you write with? As a child was this hand your natural choice? Which hand do you use to brush your teeth? In which hand do you hold a dessert spoon? Which hand do you use to stir a drink? Do you consider yourself right handed, left handed or able to use either?
3791
102/3796 (2.7%) were twins. All subjects recorded which hand they use for writing; 445/3518 (11.7%) use the left hand and 10 (0.3%) use either hand. Of these 3754 recorded their ABO blood group and 3223 their Rhesus group. There was no association between ABO group and the hand used for writing, with the proportion of subjects using their left hand being virtually identical in all blood groups (Table II). Similarly there were no differences between blood groups in whether subjects considered themselves to be left or right handed (from question 10, Table I).
The hand used for writing did not differ between the 102 twins and 3694 other subjects TABLE II
ABO Blood Group and Hand Used for Writing ABO group A
o
B
AB
Hand used for writing Right n (% of group) Left n (% of group) Either n (% of group)
1438 (88) 196 (12) 6 (0.4)
1432 (88) 187 (12) 2 (0.1)
304 (89) 36 (II)
134 (88)
Total (% of population)
1640 (44)
1621 (43)
140 (9)
153 (4)
17 (II)
2 (1.3)
TABLE III
The Influence of Twinning and Gender on Hand Used for Writing Right
Left
Either
Total
Twins n (%) Others n (%)
89 (87) 3256 (88)
II (11) 430 (12)
2 (2) 8 (0.2)
102 3694
Females n (%) Males n (%)
1762 (88) 1598 (88)
226 (11) 218 (12)
5 (0.3) 5 (0.3)
1993 1821
Hand used for writing
Handedness in blood donors
709
TABLE IV
The Influence of Age Group on Hand Used for Writing and Perceived Handedness Age category in years
<30
30-39
40-49
50+
Total n
1037
1094
1064
618
899 (87) 136 (13) 2 (0.2)
961 (88) 131 (12) 3 (0.3)
940 (88) 122 (12) 3 (0.3)
560 (91) 56 (9) 2 (0.3)
833 (80) 112 (II) 92 (9)
888 (81) 116 (11) 90 (8)
877 (82) 102 (10) 85 (8)
502 (81) 508 (8) 66 (II)
Hand used for writing right n (% in age group) left eiher Considers self to be right handed n (% in age group) left handed eitber handed
or between males and females (Table III) and there were no differences in the hand used to brush teeth, hold a dessert spoon or stir a drink. Among the twins 7 (6.9%) considered themselves left handed, compared with 369 (10.0%) of the others; this difference (as well as that for perceived right handedness) was not statistically significant. Of the males 14551 1820 (79.9%) said they considered themselves right handed, compared with 164511993 (82.5%) of females (p 0.04 by chi-squared). Thus males were significantly less likely to consider themselves right handed than females. Choice of writing hand was said to be natural (question 6, Table I) by 3706/3791 (97.8%) subjects and not natural in 73 (1.9%); the remaining 12 subjects said they could have chosen either hand. In those reporting that their choice was not natural three said they used either hand to write. Of the remaining 70, 68 (97%) reported writing with the right hand and 2 (3%) with the left. Table IV shows hand preference in different age groups. There is no significant overall trend with age but subjects aged 2:50 years were significantly more likely to write with the right hand (90.6% versus 87.6%) and less likely to use the left (9.4% versus 12.4%, p 0.03 by chi-squared in each case). They were also significantly more likely to hold a dessert spoon in the right hand (90.3% versus 86.6%, p
There was no association between blood group and either handedness for writing or perceived handedness in a study of 3815 blood donors. Thus these data cannot throw light on the location of any genetic component in the determination of handedness. Overall the proportion of the population who reported that they write with the left hand was 11.7%, within the range reported by other investigators. Blood donors may not be entirely representative of the population from which they volunteer. However, if twinning, gender or age influence handedness in the population it is unlikely that these influences would be different in this group. One in 37 of this cohort were twins, close to the 1140 previously reported for the UK population. Contrary to many reported studies (reviewed by McManus, 1980, and Bishop, 1990) we found no evidence of more left handedness or less right handedness in twins than others in this cohort. These findings also contrast with those from a study of 766 children born weighing under 1850 g (Morley et aI., submitted for publication) where there was a strong trend to more left handed writing in twins (21 %) than others (16%) at 7.5 to 8 years of age. It has been suggested that preterm twins are at greater risk of brain insult than
710
R. Morley and E.A. Caffrey
pretenn singletons but there was no evidence that this was the case. These data therefore raise the possibility that twins only have an increased rate of left handedness if they are born pretenn. The influence of gender on handedness was small, with 12.0% of males and 11.3% of females using the left hand to write. However, males were significantly less likely to consider themselves right handed (79.9% versus 82.5%, p = 0.04 by chi-squared). Ellis et al. (1988) showed that the incidence of strong right handedness increased with age as strong left handedness decreased. We found that subjects aged 50 or more were significantly more likely to use their right hand for writing or holding a dessert spoon and less likely to use the left than younger subjects. It could be argued that older subjects had been subjected, in childhood, to more social pressure to use the right hand than subjects born more recently. We found no evidence for this. The proportion of subjects reporting that they use their natural choice of hand for writing did not differ between age groups. Thus, while data from this study generally confirm the findings of others in relation to the influence of gender and age on handedness we found no evidence that subjects who had a twin were more likely to be left handed. One of the major risks associated with multiple pregnancy is premature delivery; the average length of a twin pregnancy is 20 days less than for a singleton. If the increase in left handedness in twins is associated with preterm delivery, then the inconsistent findings in twin studies may relate to population differences in the proportion born pretenn. We suggest that future studies comparing handedness in twins and singletons should record gestational age at delivery of all subjects. ABSTRACT
There has been considerable interest in the contribution of inheritance to detennination of handedness and in observed associations between hand laterality and twinning, gender and age. Unpublished data from a study of children born pretenn suggested an association between ABO blood group and handedness. A questionnaire filled in by 3815 blood donors, gave infonnation on blood group, age, gender, whether they were a twin, hand used for writing and perceived handedness. There was no association between ABO blood group or rhesus group and handednes. Significantly more females than males considered themselves right handed (82.5% versus 79.9%) and more subjects aged 50 + wrote with the right hand (90.6% versus 87.6% if younger). Twins did not differ from other subjects in this study and we hypothesise that the generally inconsistent findings relating to twins may be explained by population differences in the proportion of twins born preterm.
Acknowledgements. We are grateful to the blood donors who filled in questionnaires, East Anglian blood donor attendants who gave out and collected in forms and Professor I.e. McManus for advice during preparation of this manuscript. REFERENCES ANNETT, M. Left, Right, Hand and Brain: The Right Shift Theory. Hove: Lawrence Erlbaum, 1985. BISHOP, D.V.M. Handedness and Developmental Disorder. Hove: Lawrence Erlbaum, 1990. ELLIS, S.J., ELLIS, P.J., and MARSHALL, E. Hand preference in a normal population. Cortex, 24: 157163, 1988. McMANUS, I.C. Handedness in twins: a critical review. Neuropsychologia, 18: 347-355, 1980. McMANUS, I.C. The inheritance of left-handedness. In Ciba Foundation Symposium, 162: 251-281. Chichester: Wiley, 1991. MORLEY, R., COLE, T.J., POWELL, R., and LUCAS, A. Mother's choice to provide breast milk and developmental outcome. Archives of Disease in Childhood, 63: 1382-1385, 1988. Ruth Morley. 23 High Street, Great Shelford, Cambridge, CB2 SEH.
INTRODUCTION
There is evidence for an inherited component in the determination of handedness (McManus, 1991) but the nature and genetic location of this is uncertain. In a cohort of 766 children aged 7.5 to 8 years born weighing under 1850 g there was a trend to more left handedness for writing in children with blood group B or AB, compared with those from other blood groups (unpublished data on children froma multicentre study; Morley, Cole, Powell et aI., 1988). Although it was likely that this was a chance finding, it would be of considerable interst if confirmed in a larger population. We therefore studied a large cohort of blood donors to investigate whether there is any association between ABO blood group and handedness. Although this was our primary objective we felt that there were a number of other important issues relating to handedness which could be addressed by this study; namely the reported associations of handedness with twinning, gender and age. It has been widely reported that left handedness is more common in twins, though this has not been a consistent finding. The evidence for the influence of twinning on handedness has been reviewed by McManus (1980) and Bishop (1990). In the cohort studied by Morley et al. (1988) there was a strong trend to more left handedness among twins than in other children born preterm and it is of interest whether this same trend applies to twins in general. Right handedness is widely reported to be slightly less common in males (Annett, 1985) and more common with increasing age (Ellis, Ellis and Marshall, 1988). We have therefore also investigated the influence of twinning, gender and age on handedness in the large blood donor group. MATERIALS AND METHODS
Questionnaires were taken to blood donor sessions organised by the East Anglian Blood Transfusion Centre and donors were asked to fill one in while resting after giving blood. Donors cannot give blood at less than 3 monthly intervals and all forms were completed within a month; no subject, therefore, could have been included twice. The questions are shown in Table I. In order to detect, with 90% power, a 5% difference in left handedness between subjects with blood Groups B or AB versus other groups we calculated that 2700 subjects would be required. To allow for wastage 4000 forms were distributed among the four regional blood collection teams. Statistical analyses, for comparing proportions between groups, were by chi-squared.
RESULTS
Altogether 3815 forms were filled in and the number of subjects completing each item is shown in Table I. Median age was 39 years (25th percentile 30 and 75th 47 years). Of the 3814 subjects reporting gender 1821 (47.7%) were males and 1993 (52.3%) females; Cortex, (1994) 30, 707-710
R. Morley and E.A. Caffrey
708
TABLE [
Responses to Questionnaire
I 2 3 4 5 6
7 8 9 10
Total number completing item
Right n (%)
Left n (%)
Either n (%)
3815 3814 3796 3754 3815
3360 (88.1)
445 (11.7)
10 (0.3)
3813
3325 (87.2)
418 (11.0)
70 (1.8)
3815
3330 (87.3)
442 (11.6)
43 (1.1)
3807
3204 (84.2)
437 (11.5)
166 (4.4)
3813
3100 (81.3)
380 (10.0)
333 (8.7)
Age in years Are you male or female? Do you, or did you have a twin? What is your blood group? Which hand do you write with? As a child was this hand your natural choice? Which hand do you use to brush your teeth? In which hand do you hold a dessert spoon? Which hand do you use to stir a drink? Do you consider yourself right handed, left handed or able to use either?
3791
102/3796 (2.7%) were twins. All subjects recorded which hand they use for writing; 445/3518 (11.7%) use the left hand and 10 (0.3%) use either hand. Of these 3754 recorded their ABO blood group and 3223 their Rhesus group. There was no association between ABO group and the hand used for writing, with the proportion of subjects using their left hand being virtually identical in all blood groups (Table II). Similarly there were no differences between blood groups in whether subjects considered themselves to be left or right handed (from question 10, Table I).
The hand used for writing did not differ between the 102 twins and 3694 other subjects TABLE II
ABO Blood Group and Hand Used for Writing ABO group A
o
B
AB
Hand used for writing Right n (% of group) Left n (% of group) Either n (% of group)
1438 (88) 196 (12) 6 (0.4)
1432 (88) 187 (12) 2 (0.1)
304 (89) 36 (II)
134 (88)
Total (% of population)
1640 (44)
1621 (43)
140 (9)
153 (4)
17 (II)
2 (1.3)
TABLE III
The Influence of Twinning and Gender on Hand Used for Writing Right
Left
Either
Total
Twins n (%) Others n (%)
89 (87) 3256 (88)
II (11) 430 (12)
2 (2) 8 (0.2)
102 3694
Females n (%) Males n (%)
1762 (88) 1598 (88)
226 (11) 218 (12)
5 (0.3) 5 (0.3)
1993 1821
Hand used for writing
Handedness in blood donors
709
TABLE IV
The Influence of Age Group on Hand Used for Writing and Perceived Handedness Age category in years
<30
30-39
40-49
50+
Total n
1037
1094
1064
618
899 (87) 136 (13) 2 (0.2)
961 (88) 131 (12) 3 (0.3)
940 (88) 122 (12) 3 (0.3)
560 (91) 56 (9) 2 (0.3)
833 (80) 112 (II) 92 (9)
888 (81) 116 (11) 90 (8)
877 (82) 102 (10) 85 (8)
502 (81) 508 (8) 66 (II)
Hand used for writing right n (% in age group) left eiher Considers self to be right handed n (% in age group) left handed eitber handed
or between males and females (Table III) and there were no differences in the hand used to brush teeth, hold a dessert spoon or stir a drink. Among the twins 7 (6.9%) considered themselves left handed, compared with 369 (10.0%) of the others; this difference (as well as that for perceived right handedness) was not statistically significant. Of the males 14551 1820 (79.9%) said they considered themselves right handed, compared with 164511993 (82.5%) of females (p 0.04 by chi-squared). Thus males were significantly less likely to consider themselves right handed than females. Choice of writing hand was said to be natural (question 6, Table I) by 3706/3791 (97.8%) subjects and not natural in 73 (1.9%); the remaining 12 subjects said they could have chosen either hand. In those reporting that their choice was not natural three said they used either hand to write. Of the remaining 70, 68 (97%) reported writing with the right hand and 2 (3%) with the left. Table IV shows hand preference in different age groups. There is no significant overall trend with age but subjects aged 2:50 years were significantly more likely to write with the right hand (90.6% versus 87.6%) and less likely to use the left (9.4% versus 12.4%, p 0.03 by chi-squared in each case). They were also significantly more likely to hold a dessert spoon in the right hand (90.3% versus 86.6%, p
There was no association between blood group and either handedness for writing or perceived handedness in a study of 3815 blood donors. Thus these data cannot throw light on the location of any genetic component in the determination of handedness. Overall the proportion of the population who reported that they write with the left hand was 11.7%, within the range reported by other investigators. Blood donors may not be entirely representative of the population from which they volunteer. However, if twinning, gender or age influence handedness in the population it is unlikely that these influences would be different in this group. One in 37 of this cohort were twins, close to the 1140 previously reported for the UK population. Contrary to many reported studies (reviewed by McManus, 1980, and Bishop, 1990) we found no evidence of more left handedness or less right handedness in twins than others in this cohort. These findings also contrast with those from a study of 766 children born weighing under 1850 g (Morley et aI., submitted for publication) where there was a strong trend to more left handed writing in twins (21 %) than others (16%) at 7.5 to 8 years of age. It has been suggested that preterm twins are at greater risk of brain insult than
710
R. Morley and E.A. Caffrey
pretenn singletons but there was no evidence that this was the case. These data therefore raise the possibility that twins only have an increased rate of left handedness if they are born pretenn. The influence of gender on handedness was small, with 12.0% of males and 11.3% of females using the left hand to write. However, males were significantly less likely to consider themselves right handed (79.9% versus 82.5%, p = 0.04 by chi-squared). Ellis et al. (1988) showed that the incidence of strong right handedness increased with age as strong left handedness decreased. We found that subjects aged 50 or more were significantly more likely to use their right hand for writing or holding a dessert spoon and less likely to use the left than younger subjects. It could be argued that older subjects had been subjected, in childhood, to more social pressure to use the right hand than subjects born more recently. We found no evidence for this. The proportion of subjects reporting that they use their natural choice of hand for writing did not differ between age groups. Thus, while data from this study generally confirm the findings of others in relation to the influence of gender and age on handedness we found no evidence that subjects who had a twin were more likely to be left handed. One of the major risks associated with multiple pregnancy is premature delivery; the average length of a twin pregnancy is 20 days less than for a singleton. If the increase in left handedness in twins is associated with preterm delivery, then the inconsistent findings in twin studies may relate to population differences in the proportion born pretenn. We suggest that future studies comparing handedness in twins and singletons should record gestational age at delivery of all subjects. ABSTRACT
There has been considerable interest in the contribution of inheritance to detennination of handedness and in observed associations between hand laterality and twinning, gender and age. Unpublished data from a study of children born pretenn suggested an association between ABO blood group and handedness. A questionnaire filled in by 3815 blood donors, gave infonnation on blood group, age, gender, whether they were a twin, hand used for writing and perceived handedness. There was no association between ABO blood group or rhesus group and handednes. Significantly more females than males considered themselves right handed (82.5% versus 79.9%) and more subjects aged 50 + wrote with the right hand (90.6% versus 87.6% if younger). Twins did not differ from other subjects in this study and we hypothesise that the generally inconsistent findings relating to twins may be explained by population differences in the proportion of twins born preterm.
Acknowledgements. We are grateful to the blood donors who filled in questionnaires, East Anglian blood donor attendants who gave out and collected in forms and Professor I.e. McManus for advice during preparation of this manuscript. REFERENCES ANNETT, M. Left, Right, Hand and Brain: The Right Shift Theory. Hove: Lawrence Erlbaum, 1985. BISHOP, D.V.M. Handedness and Developmental Disorder. Hove: Lawrence Erlbaum, 1990. ELLIS, S.J., ELLIS, P.J., and MARSHALL, E. Hand preference in a normal population. Cortex, 24: 157163, 1988. McMANUS, I.C. Handedness in twins: a critical review. Neuropsychologia, 18: 347-355, 1980. McMANUS, I.C. The inheritance of left-handedness. In Ciba Foundation Symposium, 162: 251-281. Chichester: Wiley, 1991. MORLEY, R., COLE, T.J., POWELL, R., and LUCAS, A. Mother's choice to provide breast milk and developmental outcome. Archives of Disease in Childhood, 63: 1382-1385, 1988. Ruth Morley. 23 High Street, Great Shelford, Cambridge, CB2 SEH.