Genetic Testing – Genetic Screening Tests – Carrier Screening

Genetic Screening tests are blood tests that are used to identify genetic changes that can increase the risk of birth defects and genetic diseases.

Genetic diseases and birth defects occur in around 3% of pregnancies (in people with no family history of genetic disorders). Therefore, it is important to undergo genetic screening tests prior to the beginning of the pregnancy, to check for the presence of genetic anomalies that could increase the risk of hereditary diseases.

An example for one of the deadliest and most known genetic illnesses is Tay-Sachs disease that is common in Jews of Ashkenazi descent. When both parents are identified as carriers of this illness further tests are required during the pregnancy to make sure the fetus is not afflicted.

The genetic test is carried out after filling in a short questionnaire with questions about the family health history and possible illnesses. According to the answers given, women are referred to blood tests meant to eliminate genetic disorders according to their background. If the mother tests positive for one of these illnesses, her spouse may also be summoned for a similar test to see if he is also a carrier of any genetic illnesses that could be passed on to the fetus.

Genetic screening tests are highly important for any couple planning a pregnancy. Although in most cases there are no irregularities detected in these tests, it is best to perform them for your own peace of mind and for the safety of your pregnancy.

When is the test performed?

Genetic screening tests should be performed prior to the first pregnancy and before conceiving. However, they can also be taken at any stage during the pregnancy. The blood test is performed by the mother, and if the results are out of the ordinary, they must be also taken by the father to eliminate the possibility of him being a carrier of any genetic mutations. 

It is recommended taking the test before trying to conceive, since in cases of a risk of passing on any genetic disorders, the couple may prefer to consult a fertility clinic regarding using IVF with Pre-Implementation Genetic Diagnosis (also known as PGD) or may wish to perform additional tests to insure the fetus’ health.

It is important to point out that even if the test is not performed before conceiving, such as in cases of unplanned pregnancies, there is no reason to be alarmed since in most cases the results indicate no genetic disorders.

Who should undergo the test?

Any woman planning a pregnancy should undergo genetic screen tests. According to many doctors, the test should be carried out not only before the first pregnancy but should also be repeated before any subsequent attempts to conceive, due to developments in genetic research and improvements

of test technologies. In families with a known history of genetic illness, it is recommended carrying out more thorough tests, according to your geneticist’s counselling.

How is the genetic test done?

Genetic screening tests include two stages:

  • Family medical history questionnaire: the first stage of the test includes filling in a questionnaire on both families’ medical history. The couple is also asked about their ethnic descent, and about the presence of known birth defects in the family.
  • Blood test: according to the questionnaire results, blood tests are recommended to search for mutations for relevant illnesses. Since there is a great variety of genetic diseases, the diseases tested are determined according to the ethnic descent of the parents and the family medical history. 

Which diseases can be detected?

Genetic screening tests can detect many kinds of diseases. Genetic counsellors recommend the relevant tests according to the chances of being a carrier. 

The following populations should test for these diseases:

  • Most of the Jewish population – Cystic Fibrosis, SMA (Spinal muscular atrophy), Fragile X syndrome.
  • African American population – sickle cell disease
  • Mediterranean and Southeast Asian ancestry – Thalassemia
  • French Canadian ancestry – Tay-Sachs disease

For Jewish populations, further tests are recommended according to ethnic descent groups, such as:

  • Jews of Ashkenazi descent (East European): Tay-Sachs, Canavan Disease. Familial Dysautonomia
  • Jews of North African descent: Thalassemia, Tay-Sachs, PCCA (Progressive Cerebro Atrophy)
  • Jews of Yemenite descent: MLD (Metachromatic Leukodystrophy)
  • Jews of Iraqi descent: Thalassemia, PCCA, Costeff Syndrome
  • Jews of Persian (Iranian) descent: Thalassemia, Usher syndrome
  • Jews of Balkan descent: Familial Dysautonomia
  • Jews of Caucasian descent: Infantile Cerebral Cerebellar Atrophy
  • Jews of Bukahri (Central Asian) descent: Methylenetetrahydrofolate reductase deficiency

Apart from the aforementioned diseases, you can also request tests for further diseases, according to your genetic counsellor’s recommendations and your ethnic descent. Such diseases include Bloom Syndrome, Niemann–Pick disease, GSD1, Fanconi’s syndrome, etc.

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