Inbreeding and genetic disorder among Arab population

Outline: Page

I Introduction       2

II Discussion 3

III Types and reasons behind consanguinity 6

IV Conclusion 7

References 8

Introduction:

The custom of inbreeding is as ancient as the history of the human life. In fact, it was not an exception among hunter homo sapiens; it was the rule. However, humans learned from experience of its devastating affect upon the offspring. For example, none of the male children of pharaoh Akhenaton that were born out of consanguineous marriages survived. Later, Moses prohibited the marriages between siblings, mother ­son and father ­daughter (Thornill, 1993), a very courageous step in a population that had long embraced inbreeding.

The practice of interfamily mariage is still relatively common among Arabs because of the structure of the Arabic soceity. Nomadic people (Bedouins) do not really have the chance to mix with others. They are organized in tribes based on common ancestry, and when it comes to marriage, the only opportunity is to inbreed (Teebi, 1993). This social structure is common in the Arabic desert in countries like Kuwait. On the other hand, among the agricultural communities, inbreeding also commonly takes place but for different reasons. There it is favored because it ensures the unity of lands. Inheritance of land by males and females is kept within the same family, and this is of great importance for peasants because small pieces of land are inefficient in agricultural economies. This pattern is common among Lebanese, Egyptians, Palestinians, and Jordanians (Klat et al., 1984).

The consequence of consanguinity in the Arabic population is worse than typical. Although Arabs are usually identified as Caucasians, modern Arabic populations especially in Egypt, Palestine, Jordan and Lebanon, are the result of a long history of blending with different human races (Der Kalustian et al., 1980). Arabs, Africans, Europeans, and other Asian people intermarried during wars, mass migrations, trade and religious practices (pilgrimage). All in all, this kind of "out breeding" rendered Arabic populations more susceptible to genetic disorders when comes to consanguinity; because out breeding introduced different deleterious recessive alleles common among other populations beside those alleles already common among Arabs.

The impact of consanguinity is that it increases the inbreeding coefficient (Thornill et al., 1993). Thus, the chance that an individual will inherit two alleles identical by descent increases. In other words, the frequency of homozygosity increases, while the frequency of heterozygosity decreases. Because recessive disorders phenotypes are only manifested in the homozygous state, their incidence increases in inbreeding populations. In the following section, Išll discuss the degree of consanguinity and inbreeding coefficient in different Arabic populations.

Discussion:

Jordan

In a study by Khoury et al., 1992, the frequency of consanguinity in Jordan was determined to be 50.33%. The average inbreeding coefficient was 0.0225. Interestingly, the study showed that male education didnšt have much effect on consanguinity. Fourty percent of university graduate males had consanguineous marriages. However, female education seems to be mare important. Only 20% of university graduate females were married to relatives. This study also demonstrated a regressive pattern of inbreeding.A 30% consanguinity rate early in the 20th century increased at the end of the century to 50%. The pattern was also independent of religious beliefs as both Christians and Muslims showed similar results. The types of genetic diseases will be illustrated for later but basically they are very common.

Kuwait:

The Kuwaiti population is made up of Kuwaiti natives and Bedouins (40%), and immigrants from other Arabic countries and southeastern Asia (60%) (Al- Awadi et al., 1985). The incidence of consanguinity was 54.3% among Kuwaiti natives and higher among Bedouins. The average inbreeding coefficient was at least 0.0219.

Table I: The frequency of some genetic diseases in Kuwait compared to other countries. (Al-awadi et al, 1985) (OMIM) (Farag et al, 1983) (Teebi et al, 1994) (Zatz et al, 1989)

Disease Kuwait Others

Bardet-Beidel Syndrome +   

Laurence Moon Syndrome 1/50000 Switzerland: 1/150000

Meckelšs Syndrome 1/3530 Finland (na)

Duchene Muscular Dystrophy 1/ 3 of Muscular Dystrophy USA: 5% of M D

PKU 1/6479 USA+Europe:1/11000

Table I. shows the relatively common recessive disorders among the Kuwaiti population. These cases were diagnosed among Palestinians, Jordanians, Egyptians, Lebanese; as well as Kuwaitis. Thus, they might be considered representatives of these communities. Noticeable here is the higher incidence of genetics diseases even when compared to high-frequency groups. Other genetic diseases especially high in Kuwait include Cystinuria, Spinal Muscular Atrophy, Werdnig-Hoffmann G M1 Gangliosidosis and Gaucher disease type 1.Besides, there are disorders that are endemic to the Mediterranean and gulf area like Familial Mediterranean Fever (FMF) and Thalessaemia.

Egypt:

The average consanguinity rate is 28.96% with an average inbreeding coefficient of 0.010.A higher incidence of consanguinity is found in rural areas (Abdel-Gafar et al., 1983). This consanguinity rate, though lower than other Arabic countries, is still very high.

The Egyptian population has a high frequency of several genetic disorders such as Adrenal Hyperplasia, FMF, PKU, etc (Barakat et al., 1986). All of these are recessive traits. Thus, again, high rates of consanguinity lead to a higher incidence of recessive disorders.

Lebanon:

The data about Lebanon is especially interesting. It shows a consanguinity of 18% (Der Kalustian). Another study shows a higher consanguinity incidence of 26% (Teebi, 1994). But the second one was done on Lebanese workers in Kuwait. Both studies, however, demonstrated a lower incidence among Christians than among Muslims. In general, the Lebanese community is almost completely divided into subpopulations of Druze, Sunnites, Shiites (Muslim denominations) and Maronites, Greek Orthodox, Armenians (Christian denominations). Christians (about 50% of Lebanese) have a consanguinity incidence of 10% of the general population, the rest are among Muslims 90%. Despite the lower percentage of consanguinity, Lebanese still show higher incidence of genetic diseases including FMF, familial Hyperplasia, Glucose-6-Phosphate dehydrogenase deficiency, sickle cell anemia and Thalessaemia ( Der Kalustian et al., 1980). This is consistent with a high frequency of recessive disorders in the general population.

Types and Reasons Behind Consanguinity:

Among Muslims and Christians, the most common type of consanguinity is between first cousins especially from the paternal side (Teebi, 1994) (Al-Nassar et al., 1989). In fact, a common Lebanese way of complimenting the spouse is to call her/him "cousin"(Der Kalustian et al., 1980). In addition, marriages within the extended family are also common especially in villages and among Bedouins. However, aunt-nephew and uncle-nice marriages as practiced by Jews from Arabic origin, are prohibited by Islam and by state laws (Teebi et al., 1988). Genetically speaking, aunt-nephew and uncle-niece marriages result in the same inbreeding coefficient of double first cousin marriages (F=1/8) (Abdel-Gafar et al., 1983).

The question is why does the practice of consanguinity persist among Arabs in face of severe genetic consequences. Several factors might be involved here including religion, education, socioeconomic status and culture.

To begin with, most Arabs are Muslims. Many researchers tend to conclude from religious studies that Islam discourages consanguineous marriages (Teebi, 1994). I think Islam is in theory equivocal about this issue. There is a very clear teaching from Prophet Mohammed encouraging people to outbreed. On the other hand, he was very proud of his tribe. One might deduce here that onešs tribe is favored especially when it comes to marriage.

The data from Lebanon show a significant difference in the incidence of consanguinity between Christians and Muslims (Der Kalustian et al., 1980). However, most Lebanese Christians (Maronites and Armenians) do not identify themselves as Arabs. Clearly, they have different origins and cultural practices. In Jordan, however, consanguinity rates among Christians and Muslims are very similar (Khoury et al., 1992). Besides, the practice is also common among Jews of Arabic origin (Stark et al., 1984). Thus, religion is at least not the single determinant of consanguinity rate.

Another consideration is educational level. I initially thought lack of education was the reason behind consanguinity. However, the data, especially from Jordan, demonstrated that the phenomenon is independent of the degree of education. For instance, university graduates showed a consanguinity rate of 40%, which is close to that of illiterates 44%. Nevertheless, in urban populations, that traditionally have higher degree of education, there is a lower occurrence of consanguinity than among suburban and rural populations. All in all, the relationship between consanguinity rate and educational level remains indirect and thus inconclusive.

I think the consanguinity problem is culturally based. Arabs previously lived as either nomads or as peasants in agricultural villages. Both styles of living, as I mentioned before, have their reasons to inbreed. As people moved toward urban cities in the 20th century, the pattern in cultural practices and inherent mentality remained untouched. Urbanization didnšt challenge the mentality of the old out-dated system, and it didnšt offer any alternative. In fact, it even strengthened the practice with the development of modern statehood in the Arabic countries (in Jordan for example). Political leaders didnšt legitimize their rule based on public consent, elections or economic development, but rather based on the power of their tribes or tribal allies. This tradition has had a great negative impact on the general population.

Conclusion:

The high rate of consanguinity increases the inbreeding coefficient, and the frequency of genetic disorders in Arabic populations. This effects health, psychological state and economic status of many unfortunate families, and it has implications on the whole population. I thought level of education was a key causative element. But to my disappointment, It is not. Clearly, The roots of this problem go deeper. And regardless of the reasons behind it, there has to be an effort at least in the medical field and population genetics to evaluate the situation. There is a lack of research and information concerning the problem. I wasnšt able to find the frequencies of endemic genetic disease in the area like thalassemia. Besides, genetic screening has to become both available and mandatory for effected families. Finally, premarital genetic counseling could be of great importance in helping young couples understand the high risk associated with consanguineous marriages.

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