Genetic testing is relied upon more and more to detect and diagnose rare genetic conditions. Here we take a look at what it is, how it began, and its life-saving potential.
What is genetic testing?
Our bodies are made up of trillions of cells. Those cells each contain chromosomes that are composed of chemical strands known as DNA. DNA contains our genetic information. Genes are responsible for the variety of traits that make you who you are—from the color of your eyes to your shoe size to your fingerprint. DNA is our unique genetic blueprint. Sometimes, changes or mutations can occur in DNA—some are benign and some can increase a person’s risk of developing a certain disease or medical condition. It is these DNA mutations that genetic testing looks for.
When did genetic testing begin?
Chromosomes were first discovered in the late 1800s. The link between inherited diseases and chromosomes was made in the early 1900s. By the 1950s, scientists had begun to develop genetic screening for a variety of medical conditions.
What types of genetic tests are there?
There are seven main types of genetic testing:
- Forensic testing
- Diagnostic testing
- Carrier screening
- Predictive and pre-symptomatic testing
- Prenatal testing
- Pre-implantation testing
- Newborn testing
How are genetic tests carried out?
Genetic screening is usually carried out using blood samples, with skin, hair, amniotic fluid, or other bodily tissue sometimes used. The sample is usually obtained at the doctor’s office or hospital, then sent away to the laboratory. Here technicians look for changes in the chromosomes, proteins, or DNA, depending on the disorder they are testing for. The laboratory then reports its findings back to the medical practitioner.
What conditions can genetic carrier screening test for?
Genetic carrier screening can tell you whether you carry a genetic mutation that you could pass on to your child. These detectable mutations can cause a number of disorders, including:
- Cystic fibrosis
- Sickle-cell disease
- Tay-Sachs disease
- Huntington’s disease
- Fragile X syndrome
- Spinal muscular atrophy
Why is genetic screening done prior to pregnancy?
In many countries around the world, prospective parents are genetically screened as a matter of course. No one wants to think their child might be born with a disease, but that’s a sad reality for tens of thousands of parents. Testing isn’t a cure, but it can be a part of the preventative measures implemented by doctors and prospective parents to maximize the chances that the child will be born in good health.
Carrier screening is a one-off test, usually for both parents. That’s because many inherited disorders are recessive, meaning that the child must inherit the defective gene that causes the disorder from both parents. Other times, just one parent takes the genetic carrier test, to check for the presence of mutations that can be passed on to children via an autosomal dominant pattern. Only one parent need carry this mutation for it to be inherited by the child. Often, people with a family history of a specific inheritable disorder will decide to undergo genetic carrier screening prior to starting a family.
How common are genetic disorders?
It is estimated that as many as 1 in 20 people carry at least one faulty gene. It is important to bear in mind, however, that with most inheritable genetic conditions, a person must carry two copies in order to develop the condition. The fact a person carries a faulty gene will generally only be a concern if they choose to start a family.
Where a mother and father both carry the same faulty gene, there is a 50% chance of each child they have being a carrier of that gene, and a 25% chance of their child developing the condition associated with that gene.
There are some rare exceptions to this rule, in which just one parent can pass on the disease. These include:
- Tuberous sclerosis
- Type 1 neurofibromatosis
- Autosomal dominant polycystic kidney disease
- Huntington’s disease
Some genetic diseases such as Duchenne muscular dystrophy, fragile X syndrome, and hemophilia attach to the X chromosome. Because females have two X chromosomes while males have just one, the odds are that the condition will not affect female children, though they could be a carrier.
What happens if I’m a carrier for a genetic disorder?
It is important to remember that although you may carry a genetic mutation which predisposes you to a disease, you may show no sign of that disease throughout your lifetime. For recessive disorders, your child may develop the disorder if you and the other parent both carry the mutation—but again, that risk is 25%. It is far from a guarantee.
Still, being aware that you are at risk of developing or passing on a particular disorder can help you and your doctors to take pre-emptive steps to reduce the risk of the disease ever developing in you or your children. This could involve treatment or simply lifestyle changes that stack the odds in your favor. No one likes to think they might be a carrier, but forewarned is forearmed. In short, genetic testing can save lives.