Carrier Genetic Screening or Non Downs Genetic Screening

I use this term, “Non Down’s screening” to differentiate Carrier Genetic Screening from the Downs Syndrome screen that everyone talks about. Unlike Down’s syndrome screening which can only be performed during pregnancy, these screens can be undertaken at any time in a person’s life. They look for different genetic conditions that may be present in one’s genetic makeup which is not symptomatically obvious in the individual.

The genetic conditions that these screens look for are many and varied. Some are reasonably frequent in a population but many are rare or infrequent. They all carry the potential for being able to cause severe abnormalities in the baby. Some are more prevalent in certain racial or ethnic groups. Examples of the types of genetic conditions in some at risk groups include Tay Sachs in the Jewish population and Thalassemia for the Southern European and Asian groups. Others like are cystic fibrosis, is more frequent in our community. It is not well known but in Australia, 4% of the population carry one of the genes for Cystic Fibrosis. As our understanding of genetics improve due to the Human Genome Study, we have come to realise that the frequency of an individual carrying one or more such genes is higher than we think. It is estimated that each of use can carry 2-3 genes that can cause significant problems.

Whilst these screens have always been available for these at risk groups, it is only more recently that these screens have been made available for the general population.

To be affected by these genetic conditions, you need to have 2 genes in your makeup. If you only carry one gene, then you are known as a carrier. A carrier has no symptoms and would not even know they have anything of concern. Whilst a family history or being in a higher risk group can point to a potential problem, in most there is no such suggestion that a significant condition exists. This is the rationale to consider screening to detect these genes.

Screening is usually performed on the woman first. If she is found to be a carrier, then the partner is tested. Only if both are carriers of the same gene, is there a risk to their baby having the condition. If only one is a carrier, the worst that could happen is that the baby could be a carrier too. This is thus not of concern.

Examples are:

Woman is a carrier, partner is not.            Potential outcome for baby:       1: 2 chance baby is normal
1: 2 chance baby is carrier

Both are carriers:                                             Potential outcome for baby:     1: 4  chance baby is normal
1: 2  chance baby is carrier
1: 4  chance baby is affected

It is the last scenario that is important as the baby will then have the genetic condition. Unfortunately, these tests do not tell you if the baby is affected, only the risk of the baby being affected. Further testing may then be required.

Screening is easy. All it takes is a blood test. Whilst this can be done at any time, I would recommend it be performed prior to pregnancy. This is because it would allow time to check the partner. Whilst it can also be performed in pregnancy, it should be done as early as possible as the testing takes time.

There are currently 2 screens available.

  1. Basic 3 carrier screening.This is performed in Melbourne and tests for 3 genetic conditions: Cystic fibrosis, Spinal muscular Atrophy and Fragile X.Testing takes 10 days at a cost of $385.00. This is not able to be claimed from either Medicare or your Health Fund.
  2. Expanded carrier screening

A new panel of tests involving 300 + genetic conditions are now available.  The cost is approximately $475 to $500 and it takes 4 weeks for the results to come through. Again there is no rebate from Medicare or your Health Fund. There are now a number of companies offering this test. The method used are different and the number and variety of genes tested for do differ between Companies. At the moment these panel of tests are performed in the USA. this means that the specimens are collected locally and then forwarded to the US. The turn around time i 4 weeks to get a result.

A Federal Government version of this is going to be launched shortly. It is called Mackenzie’s Mission and was inspired by the efforts of the parents of baby Mackenzie. She was born in 2017 and was affected by spinal muscular atrophy. She died within 12 months of birth. Her parents were unsuspecting carriers of this gene. When they realised the importance of screening for these condition, they lobbied very successfully for a research grant of $20 million to offer carrier screening to 10,000 Australian couples. This will offer testing for about 500 genes. The likely launch date is 2020. Once the $20 million is used, then the program will cease. However, I hope there will be some form of program that will be instituted in its place but that is only a hope for the moment. For those interested in the story of Mackenzie’s Mission, you can read of the heartache and efforts of the parents on the internet. Simply type in Mackenzie’s Mission on the Net.

These tests can be performed either during or outside of pregnancy. Anyone of any age group can have these test. To be most effective, it should be performed before pregnancy. The reason is it will allow time for testing of the partner where appropriate. If both are found to be carriers of the same gene condition, then there is time for counselling to occur. Furthermore, the couple could consider IVF. Here, the embryo could be tested before being put into the woman’s womb.

If however, testing is performed during pregnancy, there is a time constraint due to the time taken for results to be obtained. If both partners are affected, to check if the baby is also affected requires an amniocentesis. This not only carries a risk of miscarriage but is performed after 15 weeks of pregnancy. Thus any affected baby cannot be detected till later in pregnancy. Should abortion be considered, it is harder, and usually involves inducing a labour.

Thus I would encourage strongly testing to be performed prior to pregnancy.

Please understand that there is no compulsion for anyone to have these tests. However, it is important that you are made aware that such testing exists so you can avail yourself of the opportunity to have them. Which test you choose ultimately is based on your personal choice. I am happy to discuss the benefits of testing and to make arrangements for you to have them performed if you wish.

These notes reflect my personal opinion and are intended for general advice only. It should not be used for any one individual case. You should consult your own doctor to determine the appropriate management of your own individual situation. No part of these notes can be used or reproduced in any manner without my express consent