Genetic counselling: from family planning to cancer prevention

Image credit: Getty Images 

Today, healthcare is becoming more personalised, and genetic counselling can play an important role if you’re planning a family, expecting a baby, or worried about inherited health conditions. 

What is the role of a genetic counsellor?

Dr Chantelle Scott, a genetic counsellor at Mediclinic Panorama, explains that genetic counsellors help individuals and families understand inherited health risks and genetic tests. They support you in dealing with a genetic diagnosis and make sure the right tests are done, and results are explained clearly.

You might consider genetic counselling in several situations, such as:

Planning a pregnancy

You and your partner might be healthy while carrying gene variants for serious conditions that can be passed onto your child. Dr Scott explains: “We all have two copies of every gene – one from our mom and one from our dad. Many people carry a few disease-causing gene variants without ever knowing it, because this copy of the gene is overshadowed by the copy of the gene working normally and keeps us healthy.

“However, if both parents carry a disease-causing variant in the same gene, there is a one in four chance they could both pass on the variant to their baby. If that happens, the baby won’t have a working copy of that gene and will develop the associated genetic syndrome.”

About 80% of babies born with a genetic condition do not have a family history of the condition. “Therefore, all couples planning a pregnancy may consider carrier screening regardless of their family history,” says Dr Scott.  This is a blood test that screens for common conditions like cystic fibrosis, spinal muscular atrophy, and sickle cell anaemia.

“If you know about the risks, it will help you make informed reproductive decisions and lead either to prevention or better management of the condition in your future children.”

During pregnancy

If you’re pregnant and older than 35, you have a higher risk of having a child with a chromosomal condition. “Your genetic counsellor will discuss various screening tests, such as an ultrasound scan or blood tests including the non-invasive prenatal test (NIPT), that can assess your risks for having a baby with a genetic or chromosomal condition like Down syndrome,” says Dr Scott.

The NIPT blood test is available from 10 weeks of pregnancy. During pregnancy, tiny fragments of the baby’s DNA circulate in the mother’s blood. The test analyses this DNA to check for extra or missing chromosomal material, which can indicate certain conditions. It doesn’t give a definite diagnosis but shows whether the risk is low or higher than expected.

“If these screening tests indicate a high risk, further invasive prenatal diagnostic testing may be discussed,” says Dr Scott. “This entails collecting a sample from the pregnancy using invasive procedures such as chorionic villus sampling (CVS) and amniocentesis. As this is invasive, it carries a small miscarriage risk of about 1 in 200.”

CVS involves placing a thin needle through the mother’s abdomen to collect a small sample of tissue from the placenta, called chorionic villi. This test is usually done between 11-13 weeks of pregnancy. Amniocentesis is performed after 15 weeks of pregnancy and involves taking a small sample of the fluid that surrounds the baby in the womb. The baby’s DNA is extracted from the collected sample and tested to confirm a genetic diagnosis. The tests either check the baby’s chromosomes to ensure the right number is present or examine specific genes to make sure they’re working properly.

When your child is diagnosed

If your child has been diagnosed with a genetic syndrome – such as Edward syndrome, Down syndrome, fragile-X syndrome, Klinefelter syndrome, neurofibromatosis, Patau syndrome and Turner syndrome – you may want to learn as much as possible about how and why it happened.

“Understanding how and why the condition happened provides information about the possibility of it happening again with a future child,” says Dr Scott. “Parents can then discuss the option of reproductive genetic testing to exclude this condition in any subsequent pregnancy.

When you have a genetic condition

If you have, or are at risk of inheriting, a genetic condition due to a strong family history, a genetic counsellor will explain the diagnosis, how it was passed down through your family, the management options plus the support available to you. “These conditions often include inherited heart conditions like familial hypercholesterolemia or neurological conditions like Huntington disease,” says Dr Scott.

The genetic counsellor reviews different testing options to ensure the most suitable and cost-effective test is chosen. They also provide psychosocial support and the opportunity to join a local support group.

If you’re at risk of carrying a cancer gene

If you’ve had cancer – especially before age 50 – and/or have several family members affected by cancer, you may be at risk of carrying a cancer-causing genetic variant. “For example, with hereditary breast and ovarian cancer (HBOC) syndrome, mutations in BRCA1 or BRCA2 genes increase your risk for breast, ovarian, prostate, and pancreatic cancers,” says Dr Scott.

With Lynch syndrome (HNPCC), mutations in mismatch repair genes (MLH1, MSH2, MSH6, PMS2 and EPCAM) leads to higher risks of colorectal, endometrial, stomach, prostate and other cancers.

“If a detailed family history suggests a genetic cancer syndrome, we discuss the available genetic testing options, including the benefits and limitations of each. When testing identifies a causative gene variant, an appropriate management plan can be put in place to prevent cancer or detect it early, before it becomes life-threatening,” says Dr Scott.

“Even if no causative gene variant is found, a genetic counsellor will assess your risk based on your family history and provide guidance on risk management to help you stay as healthy as possible.”

Types of genetic tests

“There are many different kinds of genetic tests that look at different areas of our inherited material,” says Dr Scott. “Some focus on the 46 chromosomes and others on the 20 000 genes packed on these chromosomes. Each of these tests has a role, and the choice depends on the clinical situation and what information is needed.”

Genetic counselling helps ensure the most appropriate test is selected and results are clearly explained.

Chromosomal testing

• Karyotype is the most traditional chromosome test. “It looks at all the chromosomes under a microscope to check that your baby has the correct number and they’re the right size and shape,” says Dr Scott. “It can detect conditions like Down syndrome or missing or extra chromosomes, but it can’t see very small changes.
• Chromosomal microarray is a more detailed test. Instead of looking at chromosomes under a microscope, it uses technology to scan the chromosomes for very small missing or extra pieces of genetic material. “It can pick up changes that a karyotype may miss and is often used when a baby has abnormalities seen on ultrasound,” says Dr Scott.
• Fluorescence in situ hybridisation (FISH) looks for specific chromosome conditions rather than all chromosomes. It’s often used when doctors are looking for a particular condition, such as Down syndrome. It gives results faster than a karyotype but is more targeted and not a full chromosome check.
• QF-PCR is a rapid test that checks for the most common chromosome conditions, such as extra or missing copies of chromosomes 13, 18, 21, X, and Y. “It provides quick results but doesn’t examine all chromosomes in detail,” says Dr Scott.

Gene testing

Single gene testing

Single gene tests look for genetic changes in only one gene. This test can help if you or your child has symptoms of a specific condition or syndrome that is usually or always caused by changes in the same gene. Examples include Duchenne muscular dystrophy and sickle cell anaemia. In addition, this test is an option if the causative gene variant in your family is known.

Gene panel tests

Gene panel tests look for genetic changes in many genes associated with the same condition. These genes are screened at the same time. “These tests are recommended if you or your child have symptoms related to many overlapping conditions or conditions associated with several genes,” Dr Scott explains. “Examples include primary immunodeficiency, hearing loss, retinal degeneration or epilepsy. The tests are also used if an individual has a personal or family history of several types of cancers.”

Large-scale genomic testing

There are two different kinds of large-scale genomic tests, which look for genetic changes throughout your DNA:

• Exome sequencing examines the coding areas (called the exome) of all the genes in the DNA (whole exome) or just the genes related to medical conditions (clinical exome).
• Whole genome sequencing is the largest genetic test and looks at your entire DNA, the coding and non-coding regions of the genes.

“By combining scientific knowledge with compassionate care, genetic counsellors empower you to make informed decisions that can significantly impact your health and your family's future,” says Dr Scott.