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Carrier Screening for Genetic Conditions

Most couples will have healthy children not affected by a genetic condition. Some couples, however, unknowingly pass on a faulty gene that can have devastating consequences for the health and development of their children.

A recent Australian study* found that screening of 12,000 women showed that 1 in 20 were carriers of a genetic condition and their combined risk of having a baby with one of these conditions is comparable to the risk of having baby with Down syndrome. Given this, doctors are increasingly recommending genetic carrier screening to their patients.

There are tests available before pregnancy or in early pregnancy that screen for the common genetic conditions, such as Cystic Fibrosis (CF), Spinal Muscular Atrophy (SMA) and Fragile X syndrome, through to more extensive panels that screen for hundreds of conditions. Many people are carriers of genetic conditions even though no one in their family has the condition – about 80% of children born with a genetic condition have no family history of the condition, despite there being multiple generations of family members carrying the faulty gene.

Here is a brief summary of three of the most common genetic conditions:

Cystic fibrosis (CF): is an inherited condition that primarily affects the lungs and digestive system. Individuals with CF develop an abnormal amount of thick mucus within the lungs and gut. In the lungs, this mucus traps bacteria resulting in recurrent infections. Within the gut, the mucus impairs digestion of food. Infants, children and adults with CF require daily chest physiotherapy to clear the mucus from the lungs and enzyme replacement medication to aid in food digestion. CF is a serious condition and there is no cure. Individuals with CF have a shortened life span with lung failure being the major cause of death. More information

Spinal muscular atrophy (SMA): is a condition that affects nerves in the spinal cord and causes muscles to get weaker. There are four types of SMA, with SMA type 1 being the most common and the most severe. Babies with SMA type 1 have weak muscles from birth and usually do not live past two years of age. There is no cure for SMA, however there are treatments and interventions available aimed at managing symptoms and improving quality of life.

Both Cystic Fibrosis and Spinal muscular atrophy are autosomal recessive conditions, meaning that if both parents are healthy carriers then there is a 1 in 4 chance of having an affected child. If you are a carrier of CF or SMA you have a change in one of your genes associated with these two conditions. CF and SMA carriers do not develop symptoms.

Fragile X syndrome (FXS): is the most common cause of inherited intellectual disability. People with FXS can have developmental delay, learning difficulties, anxiety, autism, epilepsy as well as some physical characteristics. Features vary from mild to severe but because FXS is located on the X-chromosome, males are more likely to be severely affected than females. There is no cure although some educational, behavioural and medical interventions can improve outcomes for people with FXS. Some female carriers may develop fertility problems and go through menopause early (less than the age of 40) and some carriers develop late onset neurological issues that can cause tremors and balance problems.

Being an X-linked condition, FXS is generally passed onto male offspring by female carriers. With each pregnancy, FXS carriers have a 1 in 4 chance of having a child with Fragile X syndrome.

If testing identifies an increased risk, couples have several options to avoid having an affected child. We can discuss these options with you.

In addition to the above common conditions there might be clues in the family history that other genetic risk exists. Couples planning a pregnancy can make an appointment with a genetic counsellor at Ultrasound Care to go through the family tree for both partners and see if any other genetic testing might be appropriate.

Genetic tests are not covered by Medicare or private health insurance. The cost of genetic screening can vary from $50 for a single gene, through to several hundred dollars per person tested for multi-gene panels. To screen for the three most common carrier conditions (CF, SMA and FXS) is $400 per person. Genetic screening for recessive and X-linked conditions should not impact health or life insurance as carriers are not affected.

Links to pictures used and online articles:
http://www.smh.com.au/national/simple-genetic-test-can-avoid-tragedy-and-should-form-part-of-all-preconception-care-20180222-p4z1bv.html
https://geneticsupportfoundation.org/archive/genetics-and-you/autosomal-recessive-inheritance
https://www.geneticsupport.org/genetics-101/inheritance-patterns/x-linked/