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, Iπll 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 didnπt 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
Meckelπs 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-6Phosphate 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, auntnephew 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 oneπs 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 didnπt challenge
the mentality of the old out-dated system, and it didnπt 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 didnπt 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 wasnπt 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.
References:
1. Abdel-Gafar; A., Awadalla; M., El-Khayat;H., El-Tahan; H., Ghoneim; M.,
Hafez; M. Consanguineous matings in Egyptian Population. Journal of Medical
Genetics, 1983;20:58-60.
2. Al-Awadi; S A.,El-Dossary; L, El-Khalefa;M., Faraj; T.I., Moussa; MA.,
Naguib; KK, Teebi;A.S. Consanguinity among the Kuwaiti population. Clinical
genetics 1985; 27: 483-6.
3. Al-Nassar; KE., El-Kazimi; A.A. Kelly; C.L. Patterns of consanguinity in the
population of Kuwait. American Journal of Human Genetics 1989; 45(suppl 4):
A0915.
4. Barakat; MH., El-Sobki; NI., Fenech; FF., Karnik; AM., Majeed;HWA,.
Familial Mediterranean fever (recurrent hereditary polyserositis) in Arabs. A study of
175 patients and review of the literature. Quarterly Journal of Medicine
1986;233:837-47.
5. Der Kalustian; VM, Loiselet; J., Naffah; J. Genetic diseases in Lebanon.
American Journal of Medical genetics 1980; 7: 187-203.
6. Farag TI, Rau VK, El-Khalifa MY, et al. Autosomal recessive Duchene-like
muscular dystrophy in Arabs. Report of a kuwaiti family and literature review. Med
Prin and pract 1989; 1: 96-101.Genetics 1983; 20: 58-60.
7. Jaber; L., Merlob; P., Bu; X., Rotter; JI., Shohat; M. Marked parental
consanguinity as a case for increased malformations in an Israeli Arab community.
American Journal of Medical Genetics 1992;44:1-6.
8.
Katznelson D. Cystic fibrosis in the Middle East. Lancet 1982;I: 112.
9. Khoury; SA., Massad; D., Consanguineous marriage in Jordan. American
Journal Medical Genetics 1992;43:769-75.
10. Klat M, Khudr A. Cousin marriages in Beirut: is the pattern changing. J Biosoc
Sci 1984;16:369-73.
11. Majeed; HA., Barakat; M.. Familial Mediterranean fever (recurrent hereditary
polyserositis) in children: analysis in 88 cases. European Journal Pediatrics 1989;
148:363-41
12. Teebe; AS. Autosomal recessive disorders among Arabs: an overview from
Kuwait. Journal of Medical Genetics, 1994; 31-224-233.
13. Teebi; AS., Marafie; MJ. Uncle-niece/aunt-nephew marriages are not existing
among Arab Muslims. American Journal of Medical Genetics 1988;30:981.
14. Teebi; AS., Farag; TI., New monogenetic disorders in a mixed Arab population.
American Journal of Human Genetics 1989;45(suppl 2):A66.
15. Teebi; AS., Daoud; AS. Multiple pterygium syndrome: a relatively common
disorder among Arabs. Journal of Medical Genetics 1990;27:791.
16. Zatz; M., Passos-Bueno; M.R., Rapaport; D. Estimate of the proportion of
Duchene muscular dystrophy with autosomal recessive inheritance. American Journal
of Medical Genetics 1989;21:407-10.
17. Teebi; AS., Al-Awadi; SA., Spondyoepiphyseal dysplasia tarda with progrssive
arthropathy: a rare disorder frequently diagnosed among Arabs. Journal of Medical
Genetics 1985;23;189-91.
18. Thornill, Nancy w (Ed.); The Natural History Of Inbreeding And Outbreeding,
The University of Chicago Press, Chicago (1993).
19. Simsek; M., Al-Nassar; KK., Olive; M.D. Incidence and genotypic distribution
of thalassemia in Kuwait. American Journal Human Genetics 1989:454(suppl
4):A0861.
20. Stark; B., Hershko; C., Rosen; N, cividalli; G, Karsai; H, Soffer; Dov. Familial
hemaphagocytic lymphohistiocytosis (FHLH) in Israel. I. Description of 11 patients
of Iranian-Iraqi origin and review of the literature. Cancer 1984;54:2109-21