What Can Your Genes Really Tell You?
In this article we explore the link between genes and disease and investigate the carrier screening process. We look at this relatively new procedure and what it can tell prospective parents about their risk of passing a genetic disorder on to their biological offspring.
The Link between Genetics and Disease
A genome is the genetic blueprint containing all of a person’s DNA information. Like fingerprints, no two genomes are the same. They dictate our physiology, how our bodies function and, to some extent, whether we are healthy or predisposed to disease.
Since the completion of the Human Genome Project at the start of the 21st century, when the human genome was first successfully sequenced, scientists have been learning more and more about the relationship between our genes and disease.
The genome contains 23 pairs of chromosomes and an estimated 22,000 genes. We inherit one copy of each chromosome from each of our parents. Genes give instructions to the body, telling it how to function. They govern our production of protein, many types of which the human body needs in order to function.
Genes also determine the way in which the body functions, e.g. digestion and reaction to medication.
Sometimes we inherit a gene mutation from one or both of our parents. Most gene mutations have little impact. The human body is incredibly resourceful: if a person inherits a faulty gene copy, the body will usually revert to the healthy copy inherited from the other parent. Nevertheless, with some gene mutations, or if a child inherits two gene copies with the same mutation, he or she could be born with a genetic disorder.
Genetic Disease Inheritance Patterns
Genetic diseases fall into two categories: recessive and dominant, with recessive disorders being more common.
When a person inherits one copy of a recessive gene mutation, he or she will carry the disease but show no symptoms. In this way, genetic disorders can arise even in families that do not have a historical association with a particular disease.
If two parents carry the same recessive gene mutation, there is a 25 percent chance that their child will be born with the disorder, a 50 percent chance that their child will be a carrier, and a 25 percent chance that their child will be born neither a carrier nor with the disorder.
Dominant genetic disorders require only one faulty gene copy in order for the child to be born with the disorder. If just one parent carries a dominant gene mutation, there is a 50 percent chance that their child will inherit the associated condition. In rare instances where both parents carry the same dominant gene mutation, the likelihood is that the embryo will be so severely affected that the pregnancy will not survive.
Dominant genetic disorders are much more traceable in terms of family history.
The Link between Genetic Disease and Ethnicity
For some time, scientists have recognized a link between genetic disease and ethnicity. Experts often attribute this to shared ancestry. Examples include: Tay-Sachs disease in people of Ashkenazi Jewish descent; cystic fibrosis in people of North European descent; sickle cell disease in people of African and Middle Eastern descent; and thalassemia in people of Mediterranean and Asian origin.
Carrier Screening As an Integral Part of Family Planning
Most genetic disorders are recessive in nature. This means they can pass through the generations unnoticed, with symptoms only arising when two carriers have a baby together. Many genetic disorders are potentially fatal. Today, genetic carrier screening plays an integral role in pregnancy, with many prospective parents opting for preconception carrier screening.
Carrier screening is the only conclusive way to determine whether or not a person carries a particular disease-associated gene mutation. The American College of Obstetricians and Gynecologists recommend carrier screening for all prospective mothers, irrespective of ethnicity or family history.
By having their genes screened in advance, prospective parents provide medical practitioners with an unparalleled overview of their genetic makeup. Genetic carrier screening can help medical practitioners assess the risk of a child inheriting a disorder or explain failed pregnancies. In the vast majority of cases, the procedure just provides parents-to-be with peace of mind.
The Genetic Carrier Screening Process
Thanks to technological advancements in recent years, preconception carrier screening is widely available today. Genetic carrier screening is a relatively straightforward and affordable process. Clinicians take a sample, usually via mouthwash, blood or buccal sample. The sample is sent away to the laboratory for professional analysis. Depending upon the complexity of the test, results can be available in as little as a few days.
Medical insurance policies often cover the cost of genetic carrier screening.
It is important to remember that while genetic carrier screening can assess risk, there are no guarantees. Where clinicians identify a risk, it does not automatically mean that a child will have, or even carry, the associated disorder. Even if both members of a couple carry the same recessive gene mutation, there is still a 75 percent chance that their child will be born symptom-free.