Introduction
Consanguinity is prevalent in many Middle Eastern and Arab cultures and societies (e.g. Hafez et al., Reference Hafez, El-Tahan, Awadalla, El-Khayat, Abdel-Gafar and Ghoneim1983; Khlat & Halabi, Reference Khlat and Halabi1986; Hamamy & Al-Hakkak, Reference Hamamy and Al-Hakkak1989; Al-Salem & Rawashdeh, Reference Al-Salem and Rawashdeh1993; El-Hazmi et al., 1995; Demirel et al., Reference Demirel, Kaplanoğlu, Acar, Bodur and Paydak1997; Al-Abdulkareem et al., Reference Al-Abdulkareem, Bener and Ballal1998; Hamamy et al., Reference Hamamy, Jamhawi, Al-Darawsheh and Ajlouni2005; Bener & Hussain, Reference Bener and Hussain2006; Barbour & Salameh, Reference Barbour and Salameh2009, Akrami et al., Reference Akrami, Montazeri, Shomali, Heshmat and Larijani2009). Some studies have shown significant differences in genetic disorders between children born to consanguineous marriage partners and those born to non-consanguineous parents (Zlotogora, Reference Zlotogora1997; Hamamy et al., Reference Hamamy, Masri, Al-Hadidy and Ajlouni2007; Jaouad et al., Reference Jaouad, Elalaoui, Sbiti, Elkerh, Belmahi and Sefiani2009), while others have found no significant differences (Al-Awadi et al., Reference Al-Awadi, Naguib, Moussa, Farag, Teebi and el-Khalifa1986; Al-Abdulkareem & Ballal, Reference Al-Abdulkareem, Bener and Ballal1998; El-Mouzan et al., Reference El Mouzan, Al Salloum, Al Herbish, Qurachi and Al Omar2008). Consanguinity has been shown to increase homozygosity and to reduce genetic variation in a group, which may protect against the expression of recessive genes that can lead to genetic disorders (Denic & Nicholls, Reference Denic and Nicholls2007).
Kuwaiti society is not different from other Middle Eastern and Arab societies. It has been shown that consanguineous marriages are practised widely in Kuwait. Over the last three decades, three studies reported consanguinity in Kuwait to be in the range of 44.8% (Al-Kandari, Reference Al-Kandari2006), 48% (Al-Thakeb, Reference Al-Thakeb1982) and 54.3% (Al-Awadi et al., Reference Al-Awadi, Moussa, Naguib, Farag, Teebi, el-Khalifa and el-Dossary1985), which is considered rather high.
El-Najjar (Reference El-Najjar1996) assumed that there must be a relationship between consanguinity and physical and mental disabilities, including deafness and blindness. However, he provided no data to support this conclusion. Other studies have shown a relationship between consanguinity and some genetic conditions and health problems such as phenylketonuria (PKU) (Teebi et al., Reference Teebi, Al-Awadi, Farag, Naguib and el-Khalifa1987), immunodeficiency disorders (White et al., Reference White, Raju and Abouna1988; Al-Herz, Reference Al-Herz2008), children's hypertension (Saleh et al., Reference Saleh, Mahfouz, Tayel, Naguib and Bin-al-Shaikh2000), beta-thalassaemia (al-Fuzae et al., Reference al-Fuzae, Aboolbacker and al-Saleh1998), protein-C and protein-S deficiency (Mohanty et al., 1996), low birth weight (Al-Awadi & Amin, Reference al-Awadi and Amin1992) and Down's Syndrome (Alfi et al., Reference Alfi, Chang and Azen1980). Other studies show higher rates of miscarriages and prenatal and neonatal losses among children born to consanguineous parents in Kuwait compared with those born to non-consanguineous parents; however, these differences were not statistically significant (Al-Awadi et al., Reference Al-Awadi, Naguib, Moussa, Farag, Teebi and el-Khalifa1986; Egbase et al., Reference Egbase, al-Sharhan, al-Othman, al-Mutawa and Grudzinskas1996).
Consanguinity in Kuwait is higher among the sub-population with Bedouin tribal roots (Radovanovic et al., Reference Radovanovic, Shah and Behbehani1999; Al-Kandari, Reference Al-Kandari2006). The Kuwaiti population has special characteristics. The population originally came from three different surrounding areas: Saudi Arabia, Iraq and Iran. The Bedouin tribal sub-population came from the Najd (the middle of the Arabian Peninsula) and Iraq. Some belong to the same tribe although they come from different regions. Muslim Shiites originally came from southern Iraq and southern Saudi Arabia, but the majority came from Iran. Muslim Shiites are the minority in Kuwait, while the tribal groups are the majority. Al-Kandari (Reference Al-Kandari2006) reported differences between Muslim Sunnis and Shiites in practising of consanguineous marriages, with a higher incidence reported by Sunnis. One explanation is that a majority of Kuwaitis come from tribal Muslim Sunnis roots. Compared with other groups, Bedouins also have a higher fertility rate (Al-Kandari, Reference Al-Kandari2007). In the Al-Jahra region of Kuwait, for instance, which has a high proportion of its population with ancestors with tribal Bedouin roots (68% of the studied sample), the occurrence of offspring with congenital malformations is high in consanguineous marriages (Madi et al., Reference Madi, Al-Naggar, Al-Awadi and Bastaki2005).
The major aim of this study is to delineate associations of consanguineous marriages with congenital disabilities in the Kuwaiti population. It examines (1) whether pattern of marriage (relatives versus non-relatives) and congenital disorders in children are statistically significantly related; (2) whether pattern of marriage (relatives and non-relatives) is significantly associated with the total prevalence of four types of congenital disability (physical, mental and deafness and blindness combined); and (3) whether differences in prevalences of disabilities occur among different population groups in Kuwait (Muslim Sunni vs Shiite, Bedouin vs non-Bedouin roots, Arabic vs non-Arabic origin).
Methods
A total of 9104 married Kuwaiti females aged 15–79 years from different backgrounds were selected at ten primary health care centres from six governorates in Kuwait (Al-Kandari, Reference Al-Kandari2006). Centres were selected randomly from a total of sixty facilities. Data were collected by a well-trained research assistant. The questionnaire was prepared for a large project study funded by Kuwait University (Al-Kandari, Reference Al-Kandari2006); additional data were collected specifically for this study.
Four major marriage categories were reported in this questionnaire: first-cousin marriage (including five sub-categories: double first-cousin marriage where the couple share their four grandparents; man marrying his mother's brother's daughter; man marrying his mother's sister's daughter; man marrying his father's brother's daughter; and man marrying his father's sister's daughter), second-cousin marriage, third-cousin marriage and non-consanguineous marriage. Participants were asked to report their religious background and roots: Muslim Sunni or Shiite, and original tribal or non-tribal affiliation. Respondents were asked to report whether their offspring suffered from congenital disabilities of four different types: physical, mental, deafness and blindness. Respondents were asked to report on four different types of congenital disabilities of their offspring. Respondents only reported disabilities their offspring were born with to ensure that these did not have environmental causes. The research assistants ensured the validity of the respondents' answers. Offspring were defined as disabled when they had physical and mental impairment that meant having any congenital physiological and mental disorder. The deafness and blindness disabilities were defined as a vision and hearing impairment or loss as a result of a congenital condition. SPSS was used for data analysis. Chi-squared analysis was the major tool of statistical analysis.
Results
Differences in frequencies of congenital disabilities were examined by pattern of marriage (relatives and non-relatives) with regard to offspring, including four types of disability: physical, mental, deafness and blindness (Table 1).
Table 1. Frequencies of congenital disabilities among offspring of consanguineous and non-consanguineous marriages using chi-squared test
The frequency of congenital disabilities in the offspring of couples from consanguineous marriages (2.9%) is higher than that of non-consanguineous marriages (2.3%) (Table 1). But this difference is not significant at the conventional 0.05 level. When consanguineous marriages are divided into three categories (first-, second- and third-cousin marriages), first-cousin marriages have the highest frequency (3.5%) of congenital disabilities compared with other kinds of marriages (2.1–2.3%). Differences across groups are significant (p<0.036). By dividing consanguineous couples into three sub-groups (first-, second- and third-cousin couples) and comparing them with non-consanguineous couples by four disability categories (physical, mental, deafness and blindness disabilities), significant differences are found for first-cousin couples in both physical (2.37; p<0.042) and mental (0.74; p<0.037) disabilities from non-consanguineous couples (Table 2). No significant differences were observed in deafness and blindness disabilities. The data show no significant differences between second- and third-cousin and non-consanguineous couples in physical, mental, deafness and blindness disabilities.
Table 2. Frequencies of different types of congenital disabilities among offspring of consanguineous and non-consanguineous marriages using chi-squared test
Table 3 lists differences in the prevalence of the total of four types of congenital disability. There are no significant differences in the percentages of offspring with congenital disabilities in consanguineous and non-consanguineous marriages across sub-population groups for the total of four types of congenital disability.
Table 3. Frequency of congenital disabilities among offspring in different sub-groups using chi-squared test
Discussion and Conclusion
Of congenital disabilities of offspring, the results show that the offspring of first-cousin marriages only have significantly higher percentages of physical and mental disabilities. No significant differences were found among couples in sub-population groups by origin, roots and religion. These results reflect the impact of sociocultural factors associated with choice of marriage partners on the health status of offspring within one society with different types of marriages.
Genetic-related conditions are more frequent in the offspring of consanguineous marriages, as shown in some studies in the region (Abdulrazzaq et al., Reference Abdulrazzaq, Bener, Al-Gazali, Al-Khayat, Micallef and Gaber1997; Al-Kandari, Reference Al-Kandari2007). The relationship between type of marriage and congenital disabilities is reinforced by the positive relationship between health symptoms in general and type of marriage. Kinship is an influential factor in determining symptoms of health within this community. This is supported by previous studies (Teebi et al., Reference Teebi, Al-Awadi, Farag, Naguib and el-Khalifa1987; Al-Kandari, Reference Al-Kandari2007). In addition, the study by Al-Awadi et al. (Reference Al-Awadi, Naguib, Moussa, Farag, Teebi and el-Khalifa1986) pointed to the high incidence of reproductive wastage as a potential factor contributing to disabilities in children; however, this finding was not statistically significant.
It is stated that ‘the closer the biological relationship is between relatives, the more likely that they will have the same faulty gene in common’ (Barlow-Stewart & Saleh, Reference Barlow-Stewart and Saleh2007, p. 2). Although differences in disability among offspring of consanguineous and non-consanguineous marriages are only borderline significant, there is a clear statistically significant difference when consanguinity is divided into three categories (first-, second- and third-cousin). First-cousin marriages only show a higher percentage of congenital disabilities among their offspring than those of second- and third-cousin marriages. By comparing each cousin couple group with non-consanguineous couples in each disability type, the data show the only significant differences are found for first-cousin couples in both physical and mental disabilities. No significant differences were found between second- and third-cousin and non-consanguineous couples. Not finding differences in other cousin types could be explained by the effect of natural selection over time in the larger kinship group, which could be faster than in small ones, especially for fetal diseases, of which disabilities could be one. This result has been supported by another study which ‘shows no significant differences in the death of offspring between consanguineous and non-consanguineous marriages’ (Al-Kandari, Reference Al-Kandari2007, p. 82). The lack of significant difference in deafness and blindness disabilities in first-cousin couples' offspring compared with other types may be related to the low frequency of these two disabilities. As stated by Al-Merjan et al. (Reference Al-Merjan, Pandova, Al-Ghanim, Al-Wayel and Al-Mutairi2005), only 412 people are registered as blind in Kuwait.
As shown in this study, first-cousin marriage is an important contributor to congenital disabilities in Kuwait. This finding confirms those of other studies (Jain et al., Reference Jain, Nalini, Chandra and Srinivasan1993; Nasir et al., Reference Nasir, Chanmugham, Tahir, Ahmed and Shinwari2004; Kanaan et al., Reference Kanaan, Mahfouz and Tamim2008; Khabori & Patton, Reference Khabori and Patton2008). As explained by Bittles (Reference Bittles2002), a population with a high rate of consanguinity will be expected to have higher rates of recessive genetic disorders, but this pattern will be negated by urbanization, which causes family size to be smaller. Marriages happen within and across all ethnic groups within Kuwait and often between those without any blood relationship. This may in part explain the lack of relationship between the second- and third-cousin marriages and congenital disabilities in their offspring, as these relationships may be more similar to the background level of consanguinity in the population. In the case of first-cousin marriages, the relationship is clear. Genetic isolation clearly increases homozygosity, leading to congenital diseases. More studies are highly recommended.
The findings of the current study show that there is no statistical significant association between pattern of marriage between groups or various social strata in the Kuwaiti population and the prevalence of disability in their offspring. This may be due to the fact that all social strata in Kuwaiti society regularly marry relatives. In spite of disparity in the relative numbers of each sub-group, consanguinity is widely practised in all social strata of Kuwait. As shown in three different studies in Kuwait, the range is from 44.8% to 54.3% (Al-Thakeb, Reference Al-Thakeb1982; Al-Awadi, Reference Al-Awadi, Moussa, Naguib, Farag, Teebi, el-Khalifa and el-Dossary1985; Al-Kandari, Reference Al-Kandari2006). It is found that first-cousin marriage is highly practised in Kuwait. Al-Thakeb (Reference Al-Thakeb1982) found that 48% of the total marriages are among relatives and 79% of them (almost 38%) are first-cousin marriages, while Al-Awadi stated 30.2% and Al-Kandari (Reference Sanghvi2006) 24.3%. It is clear that first-cousin marriage is highly practised, although data from these studies show a decline in recent years.
A possible explanation for lack of a relationship among sub-groups in Kuwait with regard to congenital disabilities may relate to several factors. For one, as stated by Barakat (Reference Barakat2008), different tribes in the Arabian Peninsula and the Arab world are not necessarily composed strictly along kinship lines and genetic relationships. Thus, ‘third-cousin’ marriages may not reflect an actual close genetic kinship, but rather may include fictive kin who introduce heterozygosity rather than additional homozygosity into the ‘family’. Second, as hypothesized by Sanghvi (Reference Sanghvi1966), consanguinity may be practised over time, which can reduce the frequency of recessive genes for a disease, and even eventually eliminate recessive traits.
