Hereditary Disorders in the Eastern Mediterranean Region

Article excerpt

Introduction

Hereditary diseases and congenital malformations have been reported to affect 2--5% of all live births; they account for up to 30% of paediatric hospital admissions, and cause about half of childhood deaths in developed countries (1). Available evidence suggests that genetic disorders are important also in countries of the Eastern Mediterranean Region. For example, a survey of paediatric inpatients in a Saudi Arabian hospital from 1985 to 1989 revealed that almost 16% had congenital anomalies and genetically determined disorders (2). Furthermore, of paediatric deaths in 1985 in a Kuwaiti hospital, 37.5% were attributed to congenital heart disease and 12.5% to single-gene disorders (3).

Several factors, including those shown below, may contribute to the high prevalence of genetically determined disorders in the region.

-- The high consanguinity rates, which increase the

risks of recessively inherited diseases and multi-

factorial disorders.

-- The high frequency of haemoglobinopathies and

glucose-6-phosphate dehydrogenase (G6PD)

deficiency, probably because of the selective

advantage of carriers against falciparum malaria.

-- The social trend of continuing to bear children up

to menopause, which increases the predisposition

to trisomies such as Down syndrome, owing to

increased maternal age; also, the incidence of

certain autosomal dominant disorders increases

with paternal age.

-- The general lack of public health measures

directed at the prevention of genetic diseases and

the dearth of genetic services.

Consanguinity studies

Consanguineous marriages are favourably looked upon in most Muslim countries, and consanguinity rates are high in Eastern Mediterranean countries. Table 1 shows the consanguinity rates and the rates of first-cousin marriages found in various countries in the region. The consanguinity rates range from 16.5% to 55%.

Table 1: Consanguinity rates and first cousin marriages in some countries

of the Eastern Mediterranean Region

                      Total consanguinity   % first-cousin
Country (ref.)             rate (%)          marriages
Egypt (4)                    29                11.4
Iraq (5)                     57.9              30
Jordan (6)                   50                32
Kuwait (7)                   54.3              30.2
Lebanon (8)
 Christians                  16.5               7.9
 Muslims                     29.6              17.3
Saudi Arabia (2, 9)          55                31.4

The rates of first-cousin marriages are closely similar (around 30%) in Iraq, Jordan, Kuwait, and Saudi Arabia. In Lebanon, the rates of consanguinity and of first-cousin marriage are higher among Muslims than Christians. Consanguinity, as defined in WHO guidelines, is a marriage between individuals who are second cousins or more closely related.(a) However, some studies on consanguinity rates include marriages between third cousins. Although this discrepancy affects the total consanguinity rate, it does not markedly alter the average inbreeding coefficient. Uniformity of the definitions used in consanguinity studies is essential for making comparisons between populations. Calculation of the average inbreeding coefficient or restricting the study to first-cousin marriages are ways of increasing the reliability of investigations. It is important, also, to define the population studies in terms of religious, ethnic and socioeconomic criteria, as well as the methods used for ascertainment.

Among the offspring of consanguineous marriages worldwide, there is an increased postnatal mortality rate and an increased frequency of congenital malformation (10)(11). Several studies have been conducted in countries of the region to investigate the risks of consanguinity on reproduction (5)(8)(9) (12)(13)(14)(15); however, because of discrepancies in the methodologies used, comparisons between the results are difficult to make. …