ENDOGAMY, CONSANGUINITY AND THE HEALTH IMPLICATIONS OF CHANGING MARITAL CHOICES IN THE UK PAKISTANI COMMUNITY

Influence of autozygosity on common disease risk across the phenotypic spectrum

Autozygosity is associated with rare Mendelian disorders and clinically relevant quantitative traits. We investigated associations between the fraction of the genome in runs of homozygosity (FROH) and common diseases in Genes & Health (n = 23,978 British South Asians), UK Biobank (n = 397,184), and 23andMe. We show that restricting analysis to offspring of first cousins is an effective way of reducing confounding due to social/environmental correlates of FROH. Within this group in G&H+UK Biobank, we found experiment-wide significant associations between FROH and twelve common diseases. We replicated associations with type 2 diabetes (T2D) and post-traumatic stress disorder via within-sibling analysis in 23andMe (median n = 480,282). We estimated that autozygosity due to consanguinity accounts for 5%-18% of T2D cases among British Pakistanis. Our work highlights the possibility of widespread non-additive genetic effects on common diseases and has important implications for global populations with high rates of consanguinity.

Fine-scale population structure and demographic history of British Pakistanis

Previous genetic and public health research in the Pakistani population has focused on the role of consanguinity in increasing recessive disease risk, but little is known about its recent population history or the effects of endogamy. Here, we investigate fine-scale population structure, history and consanguinity patterns using genotype chip data from 2,200 British Pakistanis. We reveal strong recent population structure driven by the biraderi social stratification system. We find that all subgroups have had low recent effective population sizes (Ne), with some showing a decrease 15‒20 generations ago that has resulted in extensive identity-by-descent sharing and homozygosity, increasing the risk of recessive disorders. Our results from two orthogonal methods (one using machine learning and the other coalescent-based) suggest that the detailed reporting of parental relatedness for mothers in the cohort under-represents the true levels of consanguinity. These results demonstrate the impact of cultural practices on population structure and genomic diversity in Pakistanis, and have important implications for medical genetic studies.

Diagnostic and perinatal outcomes in consanguineous couples with a structural fetal anomaly: A cohort study

INTRODUCTION

Consanguineous unions occur when a couple are related outside marriage and is associated with adverse genetic and perinatal outcomes for affected offspring. The objectives of this study were to evaluate: (i) background characteristics, (ii) uptake of prenatal and postnatal investigation and (iii) diagnostic outcomes of UK consanguineous couples presenting with a fetal structural anomaly.

MATERIAL AND METHODS

This was a retrospective and partly prospective cohort study comparing consanguineous (n = 62) and non-consanguineous (n = 218) pregnancies with current or previous fetal structural anomalies reviewed in a UK prenatal genetic clinic from 2008 to 2019. Outcomes were compared using odds ratios (OR).

RESULTS

Most consanguineous couples were of Pakistani ethnicity (odds ratio [OR] 29, 95% confidence interval [95% CI] 13-62) and required use of an interpreter [OR 9, 95% CI 4-20). In the consanguineous group, the uptake of prenatal invasive testing was lower (OR 0.4, 95% CI 0.2-0.7) and the number declining follow up was greater (OR 10, 95% CI 3-34) than in the non-consanguineous group. This likely explained the lower proportion of consanguineous couples where a final definitive unifying diagnosis to explain the fetal structural anomalies was reached (OR 0.3, 95% CI 0.2-0.6). When a diagnosis was obtained in this group, it was always postnatal and most often using genomic sequencing technologies (OR 6, 95% CI 1-27). The risk of perinatal death was greater (OR 3, 95% CI 1-6) in the consanguineous group, as was the risk of fetal structural anomaly recurrence in a subsequent pregnancy (OR 4, 95% CI 1-13). There was no difference in the uptake of perinatal autopsy or termination of pregnancy between groups.

CONCLUSIONS

Consanguineous couples are a vulnerable group in the prenatal setting. Although adverse perinatal outcomes in this group are more common secondary to congenital anomalies, despite the evolution of genomic sequencing technologies, due to a lower uptake of prenatal testing it is less likely that a unifying diagnosis is obtained and recurrence can occur. There is a need for proactive genetic counseling and education from the multidisciplinary team, addressing language barriers as well as religious and cultural beliefs in an attempt to optimize reproductive options.

Has the long-predicted decline in consanguineous marriage in India occurred?

To an extent the question posed in the title of this paper can simply be answered in the affirmative. Based on the extensive data available from the National Family Health Survey-1 (NFHS-1) conducted in 1992-93 and NFHS-4 in 2015-16 there has been a significant overall decline of some 19% in the prevalence of consanguineous marriage in India. However, when examined at state level the picture is more complex, with large reductions in consanguinity in southern states where intra-familial marriage previously has been strongly favoured, whereas in some northern states in which close kin unions traditionally have been proscribed small increases were recorded. In a country such as India, comprising an estimated 18% of the current world population and with multiple ethnic, religious, geographical and social sub-divisions, apparently contrary findings of this nature are not unexpected - especially given the major shifts that are underway in family sizes, in education and employment, and with rapid urbanization. The changing health profile of the population also is an important factor, with non-communicable diseases now responsible for a majority of morbidity and premature mortality in adulthood. The degree to which future alterations in the prevalence and profile of consanguineous marriage occur, and at what rate, is difficult to predict - the more so given the markedly diverse cultural identities that remain extant across the Sub-Continent, and ongoing intra-community endogamy.

A population-based study of inter-generational attitudes towards consanguineous marriages in north-eastern Brazil

The aim of this cross-sectional study was to investigate beliefs, attitudes and reproductive behaviours in relation to consanguinity in a population living in the backlands of north-eastern Brazil. Data were collected by face-to-face interview from 147 high school students aged 13-20 years and from 532 elderly individuals aged 60 years and over from Brejo dos Santos in the state of Paraíba in 2017. The frequency of consanguineous marriage was found to have increased over the generations, being 15.9% in the parents of the elderly participants, 17.1% in the elderly participants themselves and 20.5% in their descendants. Although 258 (50.9%) of the elderly interviewees opposed consanguineous union, 341 (65.3%) would approve of the marriage of their children with relatives. Both the young (n=108 or 78.3%) and elderly (n=398 or 80.4%) interviewees believed that consanguineous marriages were no more durable than non-consanguineous marriages (p=0.578). Additionally, 408 (82.4%) of the elderly individuals and 108 (80.6%) of the students recognized that spouses in consanguineous unions experience conflicts, just like other couples do (p=0.625). In both groups, the majority of the participants did not believe that consanguinity increased the risk of having children with disabilities. The regression of the two continuous variables 'age' and 'positive attitudes score' showed a significant correlation, suggesting that younger individuals are more susceptible to the influence of cultural factors contributing to consanguinity, such as the opinions of their parents and grandparents. The belief that consanguineous unions are more durable showed a significant difference between elderly individuals in consanguineous and non-consanguineous unions (p=0.001); the former were 2.42 more likely to believe that marriages between relatives contributes to marriage durability.

ESTIMATING THE HEALTH AND SOCIOECONOMIC EFFECTS OF COUSIN MARRIAGE IN SOUTH ASIA

The effects of marriage between biological relatives on the incidence of childhood genetic illness and mortality are of major policy significance, as rates of consanguinity exceed 50% in various countries. Empirical research on this question is complicated by the fact that consanguinity is often correlated with poverty and other unobserved characteristics of households, which may have independent effects on mortality. This study has developed an instrumental variables empirical strategy to re-examine this question, based on the concept that the availability of unmarried cousins of the opposite gender at the time of marriage creates quasi-random variation in the propensity to marry consanguineously. Using primary data collected in Bangladesh in 2006-07 and Pakistan in 2009-10, the study found that previous estimates of the impact of consanguinity on child health were biased and falsely precise. The study also empirically investigated the social and economic causes of consanguinity (including marital quality) and concludes that marrying a cousin can have positive economic effects for one's natal family, by allowing deferral of dowry payments until after marriage.

Improving case ascertainment of congenital anomalies: findings from a prospective birth cohort with detailed primary care record linkage

BACKGROUND

Congenital anomalies (CAs) are a common cause of infant death and disability. We linked children from a large birth cohort to a routine primary care database to detect CA diagnoses from birth to age 5 years. There could be evidence of underreporting by CA registries as they estimate that only 2% of CA registrations occur after age 1 year.

METHODS

CA cases were identified by linking children from a prospective birth cohort to primary care records. CAs were classified according to the European Surveillance of CA guidelines. We calculated rates of CAs by using a bodily system group for children aged 0 to <5 years, together with risk ratios (RRs) with 95% CIs for maternal risk factors.

RESULTS

Routinely collected primary care data increased the ascertainment of children with CAs from 432.9 per 10 000 live births under 1 year to 620.6 per 10 000 live births under 5 years. Consanguinity was a risk factor for Pakistani mothers (multivariable RR 1.87, 95% CI 1.46 to 2.83), and maternal age >34 years was a risk factor for mothers of other ethnicities (multivariable RR 2.19, 95% CI 1.36 to 3.54). Education was associated with a lower risk (multivariable RR 0.78, 95% CI 0.62 to 0.98).

CONCLUSION

98% of UK CA registrations relate to diagnoses made in the first year of life. Our data suggest that this leads to incomplete case ascertainment with a further 30% identified after age 1 year in our study. Risk factors for CAs identified up to age 1 year persist up to 5 years. National registries should consider using routine data linkage to provide more complete case ascertainment after infancy.