Consanguineous couples are at high risk of conceiving a child with a genetic disorder
Consanguinity is a controversial topic due to public misunderstanding complicated by exaggerated past estimates of the adverse health outcomes. Marriage between biological relatives is widely popular in many parts of the world with over 1 billion people living in countries where 20-50% of the unions are contacted between couples related as second cousins or closer while some consanguineous couples are at high risk of conceiving a child with a genetic disorder. The popularity of consanguineous marriages was attributed to social concern rather than religious or economic concern and it is influenced by the majority of respondents, television and magazines which were the major sources of health information rather than schools, family or health workers which emphasis the need for accurate and unbiased information through these channels. Second generation subjects stressed the desirability of consanguineous couples receiving health information on potential risks. In Europe and North America, the marriage between close relatives is strongly discouraged by social convention. However, this is not true in many parts of the world. Marriage between close relatives is common in areas of the world in which geographical or ethnic isolation make marriage to unrelated people difficult.
Risk between consanguineous and non-consanguineous:
It is important to note that parents who do not have any blood relation, may also be at risk of having an infant with a hereditary disease of this kind but for these marriages (non-consanguineous), the risk is much lower. Any parent who is a carrier has a 50% chance of passing the disease on to their children and second cousins have no higher risk than an unrelated couple. The conditions that are of most concern in cousin couples are recessive conditions where one defective gene is inherited from each parent. First cousins have a 1.5 to 3% increased risk of having a child with birth defects that are inherited. However, some couples may share no recessive traits and would therefore have no increased risk. Healthy parents who do not have any blood relation, has an estimated chance of 2 – 4% of having a child with a genetic disease, developmental problem or congenital defect. In contrast, in consanguineous marriages the risk is 5 – 7% depending on the degree of the relationship between the parents and their ethnicity.
Consequences of consanguineous marriages:
The products of such close marriages tend to produce an increase of the various types of genetic disorders such as birth defects, mental retardation, deafness and blindness. It can create trouble for coming offspring so it is better to avoid it and prevent your up coming generation from diseases. The diseases like chromosomal non-disjunction are un-detectable. Most of them run in families.
What screening tests need to be done before marriage?
There are no mandatory or standard pre-marital tests. However, it is a good idea to do some tests for anaemia, thyroid or sugar problems to check your general well being. Other tests would include blood grouping and Rh factor, screening for thalassaemia, sickle cell anaemia, hepatitis, sexually transmitted diseases like syphilis and AIDS. These tests should be correlated with past medical history and family history. Genetical analysis for inherited genetic variants is performed for several purposes: diagnosis of individuals with symptoms, determination of future disease risks in asymptomatic individuals, determination of genetic risks for progeny, guidance of medical treatment, research, and individual identification. Chorionic villus and amniotic fluid analysis, in some cases feotal blood from umbilical core is also used.
In all cases of consanguineous marriages genetic counseling should be offered. This is especially important if there are known diseases in the extended families or if a problem arises in pregnancy screening tests.
Reference: Bittles, A.H. and Black, M.L. (2010) The impact of consanguinity on neonatal and infant health. Early Human Development, 86 (11). pp. 737-741
Shireen Rahat Khanzada is a 3rd year student at ISRA University Hyderabad pursuing the degree of ‘Doctor of Physical Therapy’. She can be contacted at firstname.lastname@example.org