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Consanguinity
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What exactly is the information you need to find out?
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If you and your husband/wife are related, it is important that you find out exactly
what the relationship is between you and whether there are any diseases or developmental
problems within the extended family.
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Why is it significant if you are related?
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Family members share a common gene pool. This leads to an increased risk that people
who are related will carry the same defective gene. If two such people marry (a
situation known as a consanguineous marriage) and each transmits the defective gene
to the infant - who thereby receives two copies of the same defective gene - this
may result in the child's suffering from a severe genetic disease. This type of
inheritance is known as
autosomal recessive inheritance. It can occur even if the parents are unaware
that they both carry the gene, since everybody carries 1 - 3 abnormal genes. However,
these are only expressed if his/her partner also carries the same abnormal gene
(out of a total of 70,000 genes). This, of course, is a relatively low risk in the
general population, but in consanguineous marriages, the risk is higher. The risk
decreases when the parents are not first-degree relatives.
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It is important to note that parents who are not related 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.
Healthy parents who are unrelated have 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.
If in addition to the marriage being consanguineous there is a known genetic disease
in the family, the risk that such a couple will have an infant with a similar genetic
disease may be very high.
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Therefore the risk must be determined during genetic counseling.
Parents who are related have no increased risk for chromosome disorders in their
fetus. The consideration for performing
amniocentesis is therefore the same as that of a regular pregnancy.
In consanguineous marriages, it is very important to carry out genetic screening
tests for recessive diseases such as
thalassemia, Tay Sachs
disease, cystic fibrosis, etc., and in certain ethnic groups, also for
Canavan disease,
Gaucher disease, etc.
In all cases of consanguineous marriages, genetic counseling should be offered.
This is especially important if, in addition to the partners' consanguinity, there
are known diseases in the extended families or if a problem arises in pregnancy
screening tests.
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