862
European Journal of Public Health
......................................................................................................... European Journal of Public Health, Vol. 24, No. 5, 862–869 ß The Author 2013. Published by Oxford University Press on behalf of the European Public Health Association. All rights reserved. doi:10.1093/eurpub/ckt166 Advance Access published on 8 November 2013
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Potential social, economic and general health benefits of consanguineous marriage: results from the Born in Bradford cohort study Raj S. Bhopal1, Emily S. Petherick2, John Wright2, Neil Small3 1 Edinburgh Ethnicity and Health Research Group, Centre for Population Health Sciences, University of Edinburgh, Teviot Place, Edinburgh, UK 2 Bradford Institute for Health Research, Bradford Royal Infirmary, Bradford, UK 3 School of Health Studies, University of Bradford, Bradford, UK Correspondence: Neil Small, School of Health Studies, University of Bradford, Richmond Road, Bradford BD7 1DP, UK, Tel: +44 (0) 12174 236456, Fax: +44 (0) 1274 236340, e-mail: [email protected]
Background: More than 1 billion people live in societies where consanguineous marriages are common. When children are born to consanguineous unions, there is an increased probability of the expression of single-gene disorders with a recessive mode of inheritance. There are presumptive social benefits of consanguineous marriages reported in the literature. Methods: The UK’s Born in Bradford birth cohort study recruited 12 453 women at 26–28 weeks’ gestation between 2007 and 2010. In all, 11 396 completed a questionnaire, including questions about their relationship to their baby’s father. We compared Pakistani and Other ethnic groups in consanguineous relationships and Pakistani, Other and White British groups not in consanguineous relationships, calculating percentages and age-adjusted prevalence ratios (95% confidence intervals). Results: In the Pakistani group, 59.3% of women (n = 3038) were blood relatives of their baby’s father. Consanguinity was uncommon in the Other ethnic group (7.3%, n = 127) and rare (n = 5) in the White British group. Compared with non-consanguineous counterparts, mothers in consanguineous relationships were socially and economically disadvantaged (e.g. never employed, less likely to have higher education). The Pakistani consanguineous group’s social, economic and health lifestyle circumstances were equivalent to, in some cases better than, women in non-consanguineous relationships (e.g. upto-date in paying bills, or in disagreeing that they wished for more warmth in their marital relationship). The consanguineous relationship group had less separation/divorce. Rates of cigarette smoking during pregnancy were lower in mothers in consanguineous relationships. Conclusion: Debate about consanguinity should balance the potential protective effect of consanguineous relationships with established genetic risk of congenital anomaly in children.
.........................................................................................................
Introduction ore than 1 billion people live in societies where consanguineous 1 and they are a normal variant across much of the globe. In some communities, they appear to be increasing in prevalence.2,3 When children are born to consanguineous unions, there is an increased probability of the expression of single-gene disorders with a recessive mode of inheritance.3 Animal experiments, and limited data on humans, including studies in isolated, endogamous island populations, indicate that adverse effects also may be observed on a number of other health measures, e.g. raised diastolic and systolic blood pressure.3–6 As people in consanguineous marriages have been shown to be generally less educated and less well-off than their counterparts in non-consanguineous marriages, putative adverse effects need to be considered in the light of potential confounding factors.1–3,7,8 Genetic risks have fuelled sensationalist and stigmatizing reporting of consanguineous marriages. The resulting dangers were highlighted in a report published in 19919 but remained unheeded. Similar guidance was published 20 years later.10 The social function of consanguineous marriage has been of continuing interest to anthropologists.11–14 Potential consequences of consanguinity, such as the stability of the family and maintenance of income and wealth, are relevant for assessing health benefits,1,2 but there has been a relative absence of the examination of such concerns in public health research. Where evidence for possible
Mmarriages are common
benefits exists, it is mostly in qualitative research, both in the UK15 and elsewhere, including Pakistan.16 The rare quantitative research relating to the marriage itself is conflicting,1,17 although the potential economic benefits to the bride’s family are documented.18 In May 2010, the Geneva International Consanguinity Workshop recommended that ‘The presumptive social benefits of consanguineous marriages need to be confirmed by evidence based research’.2 As part of the Born in Bradford (BiB) study,19 we report an examination of the association of consanguinity with a wide range of social, economic and general health factors. More than half the babies born in Bradford’s only maternity unit have parents of Pakistani origin. A further BiB study has reported risk factors for congenital anomaly. These included consanguinity as a major risk factor even after adjusting for deprivation.20
Methods The BiB cohort The BiB study (www.borninbradford.nhs.uk) is a prospective birth cohort study that recruited pregnant women between 2007 and 2010. Full details of the study methodology have been previously reported.19 All women booked for delivery in Bradford are offered, at 26–28 weeks’ gestation, an interviewer-administered questionnaire using trained bi-lingual interviewers. In all, 9332 (81.9%) women completed the questionnaire interview in English, 1471
Results from the Born in Bradford study
(12.9%) in Urdu, 547 (4.8%) in Mirpuri or Punjabi, 11 (0.1%) in other languages and language was not recorded in 35 instances (0.3%). Sections of the interview were given to the woman to complete, and in these, rates of missing data are higher than in the interviewer-completed sections. Mothers self-reported their ethnicity, where they and the father of the baby were born and their age on moving to the UK (if applicable). The interview included the following question: ‘Are you related to the father of your baby? For example are you cousins?’ Other questions were mostly from standard sources and have been previously described.21 All participants gave free and informed consent. Ethics approval for the study was provided by the Bradford National Health Service (NHS) Research Ethics Committee (ref 06/Q1202/48).
Data preparation and statistical design/analysis We categorized our populations by ethnic group as White British, Pakistani and Other. The Other group is heterogeneous, the largest subgroups being Indian and Bangladeshi. This group is included to check whether the associations with consanguinity were specific to the Pakistani populations. In the White British group, we excluded the five women in consanguineous relationships. We stratified the Pakistani and Other groups as either in or not in consanguineous relationships. Consanguineous relationships were those where the mother was related to the father of the baby other than by marriage, specifically, first or second cousin, first cousin once removed and other related by blood, although the majority were first cousins (see discussion on this point). Those related but not blood relatives were placed in the non-consanguineous group. Birthplace and age moved to the UK were ascertained and a composite variable was developed and coded as 1 if the mother was either born in the UK or moved to the UK aged 5 or less or coded as 2 if mother had moved to the UK aged greater than 5 years. Questions on financial stability do not include a figure on overall family income because, in piloting the questionnaire, it was evident that there were high levels of ‘don’t know’, particularly in Pakistani respondents. Also many households included extended families and hence there was a difficulty in deciding whose income to include. For categorical variables, we examined numbers with percentages, including the White British group for comparison. We used log-binomial regression to calculate, for each of the Pakistani and Other groups separately, age-adjusted prevalence
863
ratios with 95% confidence intervals (CIs), using the non-consanguineous population in each ethnic group as the reference standard. These analyses used the glm command with a log link and a binomial distribution in Stata SE 12.1.22 As a secondary analysis, we examined the data for first cousins only. For continuous variables, we calculated means with 95% CI, adjusted for age. In our tables, PR refers to the prevalence ratio of the outcome in the consanguineous compared with the non-consanguineous group within each of the ethnic group categories. In tables 2 and 3, where the numbers of non-response, don’t know and do not wish to answer responses were small when added together (
European Journal of Public Health
......................................................................................................... European Journal of Public Health, Vol. 24, No. 5, 862–869 ß The Author 2013. Published by Oxford University Press on behalf of the European Public Health Association. All rights reserved. doi:10.1093/eurpub/ckt166 Advance Access published on 8 November 2013
.........................................................................................................
Potential social, economic and general health benefits of consanguineous marriage: results from the Born in Bradford cohort study Raj S. Bhopal1, Emily S. Petherick2, John Wright2, Neil Small3 1 Edinburgh Ethnicity and Health Research Group, Centre for Population Health Sciences, University of Edinburgh, Teviot Place, Edinburgh, UK 2 Bradford Institute for Health Research, Bradford Royal Infirmary, Bradford, UK 3 School of Health Studies, University of Bradford, Bradford, UK Correspondence: Neil Small, School of Health Studies, University of Bradford, Richmond Road, Bradford BD7 1DP, UK, Tel: +44 (0) 12174 236456, Fax: +44 (0) 1274 236340, e-mail: [email protected]
Background: More than 1 billion people live in societies where consanguineous marriages are common. When children are born to consanguineous unions, there is an increased probability of the expression of single-gene disorders with a recessive mode of inheritance. There are presumptive social benefits of consanguineous marriages reported in the literature. Methods: The UK’s Born in Bradford birth cohort study recruited 12 453 women at 26–28 weeks’ gestation between 2007 and 2010. In all, 11 396 completed a questionnaire, including questions about their relationship to their baby’s father. We compared Pakistani and Other ethnic groups in consanguineous relationships and Pakistani, Other and White British groups not in consanguineous relationships, calculating percentages and age-adjusted prevalence ratios (95% confidence intervals). Results: In the Pakistani group, 59.3% of women (n = 3038) were blood relatives of their baby’s father. Consanguinity was uncommon in the Other ethnic group (7.3%, n = 127) and rare (n = 5) in the White British group. Compared with non-consanguineous counterparts, mothers in consanguineous relationships were socially and economically disadvantaged (e.g. never employed, less likely to have higher education). The Pakistani consanguineous group’s social, economic and health lifestyle circumstances were equivalent to, in some cases better than, women in non-consanguineous relationships (e.g. upto-date in paying bills, or in disagreeing that they wished for more warmth in their marital relationship). The consanguineous relationship group had less separation/divorce. Rates of cigarette smoking during pregnancy were lower in mothers in consanguineous relationships. Conclusion: Debate about consanguinity should balance the potential protective effect of consanguineous relationships with established genetic risk of congenital anomaly in children.
.........................................................................................................
Introduction ore than 1 billion people live in societies where consanguineous 1 and they are a normal variant across much of the globe. In some communities, they appear to be increasing in prevalence.2,3 When children are born to consanguineous unions, there is an increased probability of the expression of single-gene disorders with a recessive mode of inheritance.3 Animal experiments, and limited data on humans, including studies in isolated, endogamous island populations, indicate that adverse effects also may be observed on a number of other health measures, e.g. raised diastolic and systolic blood pressure.3–6 As people in consanguineous marriages have been shown to be generally less educated and less well-off than their counterparts in non-consanguineous marriages, putative adverse effects need to be considered in the light of potential confounding factors.1–3,7,8 Genetic risks have fuelled sensationalist and stigmatizing reporting of consanguineous marriages. The resulting dangers were highlighted in a report published in 19919 but remained unheeded. Similar guidance was published 20 years later.10 The social function of consanguineous marriage has been of continuing interest to anthropologists.11–14 Potential consequences of consanguinity, such as the stability of the family and maintenance of income and wealth, are relevant for assessing health benefits,1,2 but there has been a relative absence of the examination of such concerns in public health research. Where evidence for possible
Mmarriages are common
benefits exists, it is mostly in qualitative research, both in the UK15 and elsewhere, including Pakistan.16 The rare quantitative research relating to the marriage itself is conflicting,1,17 although the potential economic benefits to the bride’s family are documented.18 In May 2010, the Geneva International Consanguinity Workshop recommended that ‘The presumptive social benefits of consanguineous marriages need to be confirmed by evidence based research’.2 As part of the Born in Bradford (BiB) study,19 we report an examination of the association of consanguinity with a wide range of social, economic and general health factors. More than half the babies born in Bradford’s only maternity unit have parents of Pakistani origin. A further BiB study has reported risk factors for congenital anomaly. These included consanguinity as a major risk factor even after adjusting for deprivation.20
Methods The BiB cohort The BiB study (www.borninbradford.nhs.uk) is a prospective birth cohort study that recruited pregnant women between 2007 and 2010. Full details of the study methodology have been previously reported.19 All women booked for delivery in Bradford are offered, at 26–28 weeks’ gestation, an interviewer-administered questionnaire using trained bi-lingual interviewers. In all, 9332 (81.9%) women completed the questionnaire interview in English, 1471
Results from the Born in Bradford study
(12.9%) in Urdu, 547 (4.8%) in Mirpuri or Punjabi, 11 (0.1%) in other languages and language was not recorded in 35 instances (0.3%). Sections of the interview were given to the woman to complete, and in these, rates of missing data are higher than in the interviewer-completed sections. Mothers self-reported their ethnicity, where they and the father of the baby were born and their age on moving to the UK (if applicable). The interview included the following question: ‘Are you related to the father of your baby? For example are you cousins?’ Other questions were mostly from standard sources and have been previously described.21 All participants gave free and informed consent. Ethics approval for the study was provided by the Bradford National Health Service (NHS) Research Ethics Committee (ref 06/Q1202/48).
Data preparation and statistical design/analysis We categorized our populations by ethnic group as White British, Pakistani and Other. The Other group is heterogeneous, the largest subgroups being Indian and Bangladeshi. This group is included to check whether the associations with consanguinity were specific to the Pakistani populations. In the White British group, we excluded the five women in consanguineous relationships. We stratified the Pakistani and Other groups as either in or not in consanguineous relationships. Consanguineous relationships were those where the mother was related to the father of the baby other than by marriage, specifically, first or second cousin, first cousin once removed and other related by blood, although the majority were first cousins (see discussion on this point). Those related but not blood relatives were placed in the non-consanguineous group. Birthplace and age moved to the UK were ascertained and a composite variable was developed and coded as 1 if the mother was either born in the UK or moved to the UK aged 5 or less or coded as 2 if mother had moved to the UK aged greater than 5 years. Questions on financial stability do not include a figure on overall family income because, in piloting the questionnaire, it was evident that there were high levels of ‘don’t know’, particularly in Pakistani respondents. Also many households included extended families and hence there was a difficulty in deciding whose income to include. For categorical variables, we examined numbers with percentages, including the White British group for comparison. We used log-binomial regression to calculate, for each of the Pakistani and Other groups separately, age-adjusted prevalence
863
ratios with 95% confidence intervals (CIs), using the non-consanguineous population in each ethnic group as the reference standard. These analyses used the glm command with a log link and a binomial distribution in Stata SE 12.1.22 As a secondary analysis, we examined the data for first cousins only. For continuous variables, we calculated means with 95% CI, adjusted for age. In our tables, PR refers to the prevalence ratio of the outcome in the consanguineous compared with the non-consanguineous group within each of the ethnic group categories. In tables 2 and 3, where the numbers of non-response, don’t know and do not wish to answer responses were small when added together (
