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Introduction to cystic fibrosis, Gaucher disease, Canavan disease, Familial dysautonomia, Bloom syndrome and Fanconi anemia |
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There is no clinical connection between these diseases, but they are all transmitted in the
same manner: by autosomal recessive inheritance.
In this inheritance pattern, an affected infant will only be born if both his parents carry
the gene for the disease.
This can only be detected by genetic tests.
The carrier parents are healthy and do not show any signs of the disease, but there
is a 25% risk in every pregnancy that the infant will be affected.
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Carrier status can be identified by means of blood tests.
If both parents are found to be carriers of the same disease, prenatal testing
(chorionic villus sampling or
amniocentesis) should be carried out in every pregnancy
to determine whether or not the fetus is affected.
In order to determine whether both parents are carriers of the same abnormal gene,
the first step is to test one of them for carrier status.
Only if the parent tested is found to be a carrier will the other be tested.
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If both parents are found to be carriers of the same abnormal gene,
they are referred to a genetic counseling clinic in order to
discuss the implications and the advisability of undergoing prenatal diagnosis in every pregnancy.
It is recommended that the tests for parental carrier status be performed before or
right at the beginning of pregnancy.
This enables prenatal diagnosis to be carried out in the early stages of pregnancy
(chorionic villus sampling can be performed in weeks 10 - 11), if required.
The tests for carrier status only need to be performed once, and not in every pregnancy.
However, within the past year, new mutations in the genes for cystic fibrosis and Gaucher disease
have been discovered, so that those people who underwent tests for carrier
status of these diseases before year 2001 are advised to be tested again in any future
pregnancies for the newly discovered mutations, as well as to be tested for other diseases.
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