Introduction
It is suggested that consanguinity (union of individuals having at least one common ancestor) has been a long-standing social habit among populations (Saadat, Reference Saadat2007, Reference Saadat2008). The prevalence and patterns of consanguineous marriage depend on several demographic, religious, cultural and socioeconomic factors (Bittles, Reference Bittles2001, Reference Bittles2003; Saadat, Reference Saadat2007).
Although the rate of consanguineous marriage has declined markedly in many parts of the Western world (Bittles, Reference Bittles2003), it is still very common among African and Asian countries (Khouri & Massad, Reference Khoury and Massad1992; Bittles, Reference Bittles2001; Saadat et al., Reference Saadat, Ansari-Lari and Farhud2004; Othman & Saadat, Reference Othman and Saadat2009; Rafiee & Saadat, Reference Rafiee and Saadat2011). There are only two reports concerning consanguinity in the Islamic Republic of Afghanistan (commonly known as Afghanistan) (Wahab et al., Reference Wahab, Ahmad and Shah2006; Saify & Saadat, Reference Saify and Saadat2012). The prevalence of consanguineous marriages in Afghanistan is very high. Wahab et al. (Reference Wahab, Ahmad and Shah2006) reported the consanguinity from Nangarhar and Kunard provinces using a small sample size (168 couples). They reported that the mean inbreeding coefficient (α) in Afghanistan was 0.0332 (Wahab et al., Reference Wahab, Ahmad and Shah2006). Recently Saify & Saadat (Reference Saify and Saadat2012) reported on the consanguineous marriages in eight provinces of Afghanistan (Badakhshan, Baghlan, Balkh, Bamyan, Kabul, Kunduz, Samangan and Takhar). Interestingly, these provinces were mainly located in the east, north and north-east of the country. For this reason, the present study was conducted to determine the prevalence and patterns of consanguineous marriages in the west, south and south-east provinces of Afghanistan.
Methods
The present cross-sectional study was carried out in 2011 and 2012. For sampling a multistage design was used. Afghanistan is divided into 34 provinces. Nine provinces (Farah, Ghazni, Herat, Hilmand, Kabul, Kandahar, Logar, Parwan and Wardak) were included in the survey (Fig. 1). The selected provinces (clusters) were stratified into urban and rural areas. A total of 5200 couples (urban areas: 3151 couples; rural areas: 2049 couples) were included in the study. Data on consanguineous marriages and ethnicity (Pashtuns, Tajiks, Hazaras, Turkmens and Sadats) were collected using a simple questionnaire by interview. The questionnaires were completed by trained interviewers.
Fig. 1. Geographical distribution of study provinces in the Islamic Republic of Afghanistan. The map shows the mean of inbreeding coefficients (α) in provinces of Afghanistan from the present study and also from a previous study (Saify & Saadat, Reference Saify and Saadat2012).
The coefficient of inbreeding (F) is the probability that an individual has received both alleles of a pair from an identical ancestral source, or the proportion of loci at which he is homozygous. Consanguineous marriages were classified by the degree of relatedness between couples: double first cousins (F=1/8), first cousins (F=1/16), first cousins once removed (F=1/32), second cousins (F=1/64) and beyond second cousins (F<1/64). The mean inbreeding coefficient (α) was calculated for the population. Chi-squared contingency tests were used to compare mating pattern frequencies between populations. A probability of less than 0.05 was considered statistically significant.
Results
Table 1 shows the prevalence of the various types of consanguineous marriages in Afghanistan according to geographic locations. There was significant difference between provinces for frequencies of the types of marriages (χ 2=242.1, df=40, p<0.001). Overall the proportion of consanguineous marriages in the country was 59.3%. The mean inbreeding coefficient (α) in the country was 0.0226, ranging from 0.0203 in Farah province to 0.0246 in Herat province.
Table 1. Prevalence of various types of consanguineous marriages in Afghanistan
Numbers in parentheses are percentage of types of marriages.
The present data show that the overall frequency of consanguinity was 56.8% in urban and 63.2% in rural areas. The equivalent α values were 0.0223 and 0.0230 in urban and rural areas, respectively. There was significant difference between urban and rural areas for the types of marriages (χ 2=55.8, df=5, p<0.001).
Table 2 shows the prevalence of the various types of marriages among ethnic groups in Afghanistan. There was significant difference between ethnic groups for the types of marriages (χ 2=282.8, df=25, p<0.001). Tajiks (Soni) and Sadats showed the lowest (α=0.0215) and highest (α=0.0242) levels of consanguineous marriages among ethnic groups in Afghanistan.
Table 2. Prevalence of various types of consanguineous marriages among different ethnic groups of Afghanistan
Overall, first cousin marriages (21.7%) were the most common type of consanguineous marriages, followed by second cousins (16.0%), first cousins once removed (14.0%), beyond second cousins (6.9%) and double first cousins (1.6%).
Discussion
Here the prevalence of consanguinity in nine provinces of west, south and south-east Afghanistan is studied. Previously, nine other provinces (Badakhshan, Baghlan, Balkh, Bamyan, Kunduz, Samangan, Takhar, Nangarhar and Kunard), located in the east and north of Afghanistan, were studied (Wahab et al., Reference Wahab, Ahmad and Shah2006; Saify & Saadat, Reference Saify and Saadat2012). The present results show that the prevalence of consanguineous marriages in Afghanistan is high (Table 1), confirming the findings of previous studies (Wahab et al., Reference Wahab, Ahmad and Shah2006; Saify & Saadat, Reference Saify and Saadat2012). Although there are no data on other parts of Afghanistan, it is probable that in other parts of Afghanistan the frequency of consanguinity is high, as in the study provinces. Figure 1 shows the mean of inbreeding coefficients (α) in provinces of Afghanistan from the present study and the previous study by Saify & Saadat (Reference Saify and Saadat2012). From comparison of the provinces of Afghanistan for levels of α, it seems that α is higher in the north and north-east provinces compared with the south and west provinces of the country.
It is well established that consanguinity is strongly preferred in many Asian and African countries, including Islamic countries (Saha & El Sheikh, Reference Saha and El Sheikh1988; Khoury & Massad, Reference Khoury and Massad1992; Saadat et al., Reference Saadat, Ansari-Lari and Farhud2004; Tadmouri et al., Reference Tadmouri, Nair, Obeid, Al Ali, Al Khaja and Hamamy2009). Based on a previous report from Iran (Saadat et al., Reference Saadat, Ansari-Lari and Farhud2004), there is a high frequency of consanguineous marriages in the Turkmen population (α=0.0218), which is comparable with the prevalence of consanguinity among the Turkmen population of Afghanistan (α=0.0230). Consanguinity rate is higher among Iranian Baluchis (α=0.0294), who live in the east of Iran (Saadat et al., Reference Saadat, Ansari-Lari and Farhud2004), compared with the west and south-west provinces of Afghanistan (Table 1). Overall, the prevalence of consanguinity in Afghanistan (α=0.0226) is higher than that reported from Iran (α=0.0185; Saadat et al., Reference Saadat, Ansari-Lari and Farhud2004). Mian & Mushtaq (Reference Mian and Mushtaq1994) reported the prevalence of consanguinity in Quetta in Pakistan, which is located near Kandahar. In the present study, a higher rate of consanguinity was found for Kandahar (α=0.0232) than reported for Quetta (α=0.0217) by Mian & Mushtaq (Reference Mian and Mushtaq1994). The prevalence of consanguinity in other parts of Pakistan (Bittles et al., Reference Bittles, Grant and Shami1993) may be higher than in Afghanistan.
Consanguinity has been a long-standing social habit among populations (Bittles, Reference Bittles2001; Akrami & Ostai, Reference Akrami and Osati2007; Saadat, Reference Saadat2008). Attitude and practice toward consanguinity is deeply correlated with the historical background of a population (Bittles, Reference Bittles2001, Reference Bittles2003; Saadat, Reference Saadat2007, Reference Saadat2008). Similar to previous reports from Afghanistan, this study found a statistically significant difference between ethnic groups for prevalence of consanguineous marriages (Table 2). The difference between ethnic groups may be interpreted by differences in several demographic, cultural and socioeconomic factors.
The present study shows that there is a difference between rural and urban areas for prevalence of consanguinity, which is in agreement with reports from several other countries (Khoury & Massad, Reference Khoury and Massad1992; Othman & Saadat, Reference Othman and Saadat2009) and a previous report from Afghanistan (Saify & Saadat, Reference Saify and Saadat2012).
Because parental consanguineous marriage is associated with increased risk of recessive traits, and might also be associated with many multifactorial diseases (Bittles, Reference Bittles2001; Alper et al., Reference Alper, Erengin, Manguoglu, Bilgen, Cetin, Dedeoglu and Luleci2004; Saadat, Reference Saadat2005; Saadat & Zendeh-Boodi, Reference Saadat and Zendeh-Boodi2006; Tadmouri et al., Reference Tadmouri, Nair, Obeid, Al Ali, Al Khaja and Hamamy2009; Nafissi et al., Reference Nafissi, Ansari-Lari and Saadat2010, Reference Nafissi, Ansari-Lari and Saadat2011; Saadat, Reference Saadat2011; Ul Haq et al., Reference Ul Haq, Jalil, Hashmi, Jumani, Imdad and Jabeen2011), there is an urgent need for public education programmes and more facilities for genetic counselling and reproductive risk assessment. The incidence of consanguinity and of first cousin marriages is found to be very high in Afghanistan.
Acknowledgments
The authors are indebted to the participants for their close co-operation. The authors would like to acknowledge the trained interviewers for their assistance during the course of this study. The authors are indebted to Dr Maryam Ansari-Lari for critical reading of the manuscript. This study was supported by Shiraz University.
