Genetic Testing for Inherited Diseases When Planning for Pregnancy
Most babies are born healthy. The American College of Obstetricians and Gynecologists (ACOG) nevertheless recommends reviewing family medical history and considering genetic testing in case people want more personalized information about their chances to have a child with a birth defect or problem with development. However, genetic testing does not detect everything, and not every prospective parent wants genetic testing. It’s important to understand what genetic conditions and inherited diseases are and what genetic testing can detect.
Why should people planning for pregnancy know about inherited diseases?
No one wants to think about anything going wrong in a pregnancy. Most pregnancies will result in a healthy baby. However, about 3-5% have a birth defect or problem with development. There are some common sense steps that prospective parents can take to protect their future families.
People with inherited diseases in their families may be able to have genetic testing. If the family medical background or genetic testing shows there is an inherited disease in the family, the prospective parents may obtain better information about the chances to have a child with the condition.
The number of treatments available for inherited diseases is growing, but early diagnosis is often important to be sure those treatments are as effective as possible.
An important reason to consider the chances to have a child with an inherited condition is the possibility of treating an inherited disease. Some conditions that formerly had no treatment now have treatments or promising drugs in clinical trials. However, a definite diagnosis is critical to get access to those treatments. Unfortunately, inherited diseases are often rare, so there is often a delay in diagnosis. Reviewing family medical background and considering genetic testing can help gain access to the best medical care if a child does have an inherited condition. Also, there are specialists in specific inherited diseases who know how to best manage the symptoms in order to help people with inherited diseases reach their greatest potential.
In vitro fertilization (IVF) can be used for couples with normal fertility who want to test embryos for certain inherited conditions.
Another benefit of knowing about inherited diseases in the family is to increase family planning options. Many people don’t realize that IVF can be used for genetic testing on embryos even if a couple has no fertility issues. Others may use IVF to choose an egg or sperm donor to avoid passing the inherited condition in their family. Still others may consider adoption or even decide not to have children. Of course, for those who are already pregnant, testing a pregnancy is an option, too, but planning ahead can increase options and allow more time for decisions. Family planning can create anxiety, so the more time a couple allows to gather family medical background, discuss options with a genetic counselor, and consider genetic testing, the less pressure the couple may feel.
What are inherited diseases?
Most people have a sense of what it means for something to be genetic or inherited. Inherited traits and conditions run in families. The challenge is that the term “inherited disease” is used in different ways by different people. When they hear the term “genetic disease” or “inherited disease”, many people think about conditions like diabetes or heart disease. On the other hand, medical professionals sometimes use the term more narrowly to refer to diseases caused by single genes. It’s helpful to understand the difference to figure out whether having a family medical background of a certain disease type means you have a higher chance for that disease and what type of genetic testing is available. People don’t have to figure it out on their own though. A licensed genetic counselor can review their family medical background and advise about whether there is genetic testing that is right for them.
How common are inherited diseases?
Many genetic or inherited diseases are individually rare, but when you add them all up, they are common. About 1 in 16 people in the United States has a rare disease, and almost half of those are genetic or inherited. (Actual numbers may be higher given the difficulty of diagnosing rare diseases.)
How does someone know if they have an inherited disease in their family?
People don’t need to figure out on their own if medical problems in any family members are inherited or a risk to a current or future pregnancy. The important thing is to ask family members whether they have heard of anyone in the family, living or deceased, with a serious health problem, birth defect, or inherited disease, and if so, what was its name and its symptoms.
A genetics expert like a genetic counselor, can help assess whether a health issue in a family is likely to pose a risk for a future child or pregnancy.
Some examples of childhood conditions are:
Physical birth defects, like heart defects, spina bifida, limb abnormalities, or kidney problems
Severe learning problems, autism, or delays in development
Nerve or muscle problems
Growth problems, like unusually short or tall
Disabilities like significant vision or hearing loss
Young losses, like children, adolescents, or young adults who died
Known inherited disease in the family
DNA testing for health or medical reasons
Some examples of adult conditions are:
Cancer, including what type
Heart disease, such as heart attack, stroke, or a burst or torn blood vessel
Nerve or muscle disorder
Dementia or Alzheimer’s disease
Psychiatric conditions like depression or schizophrenia
Autoimmune disorders like lupus, type 1 diabetes, or multiple sclerosis
Known inherited disease in the family
DNA testing for health or medical reasons
To help your medical team (including a genetic counselor) to assess the chance for a serious health condition that could affect a pregnancy, it is important to ask some specific questions about the family member and the condition. If the answers are not known, it’s fine to just state that it’s unknown. Asking is still helpful. Examples of these questions are:
Was there a specific diagnosis?
What was the age of onset of symptoms or the age of diagnosis?
Is the person living or not? If family members with the health condition are deceased, note the ages and causes of death. If they are living, note their ages at the time of your discussion.
What were the symptoms?
Are there any medical records available?
Was there any genetic or DNA testing done?
Mainstream Genomics Family Screens are one way to access a genetic counselor to review family health history when planning for pregnancy.
What are some examples of inherited diseases?
There are different types of inherited diseases.
Common diseases with a genetic component
When they hear “inherited disease”, many people will think of diabetes or heart disease because they tend to run in families. That is true. Most people with conditions like diabetes or heart disease have them because of a number of different factors. Some of these factors come from lifestyle choices like exercise and diet, but genetics play a role, too. There are many genetic factors that contribute to conditions like diabetes and heart disease, but most of them are not well understood by scientists yet. We know with certainty that many genes play a role in disease like diabetes and heart disease, but we don’t yet know which or all genes or exactly what their role is.
Common diseases like diabetes and heart disease have what is called multifactorial inheritance, which means that they result from a combination of many genetic and other factors, or “many factors”.
To understand multifactorial inheritance, think about a glass of ice water. Pretend that the ice represents the genetic factors, and the water represents non-genetic factors, like diet, exercise, or other lifestyle factors. If you have a lot of ice, or genetic factors, it won’t take as much water to fill the glass to spill over. If you don’t have many ice cubes, you can add a lot more water before the glass overflows. The same is true with genetic factors for most cases of conditions like diabetes or heart disease. If a person has a lot of genetic factors, it won’t take as many other factors, like diet, to “spill over” to cause disease.
People with a family medical background that includes one of these common diseases that tends to run in families have a higher chance to develop these conditions, too. Their chances are not 100% because they can modify their lifestyle to lower their chances and they will receive varying amounts of genetic factors from their parents. (In other words, they probably won’t receive enough ice to fill their glasses with ice alone!)
Genetic testing is not typically offered for common diseases with multifactorial inheritance. For most diseases, scientists have not yet identified all of the genetic factors that could determine whether a person develops the disease. In other cases, it is not clear what people and their doctors would do differently with that information. It’s important to also realize though that among the population that has common diseases, a small portion may have a rare inherited single gene form and could benefit from genetic testing and different disease management. A genetic counselor could help determine if a family falls in this category.
Rare, single gene disorders
When medical professionals talk about inherited diseases, they sometimes mean rare, single gene disorders. Examples of these are conditions like sickle cell anemia, cystic fibrosis, Huntington disease, neurofibromatosis, and many, many more. The list of rare single gene disorders is very long.
Genes are made up of DNA, the blueprint that determines how a body grows, develops, and functions. Genes are passed from one generation to the next in a family. Sometimes there is a difference, called a DNA variant, in a gene, which causes the gene to not work properly. There are different ways these non-working genes can affect a person’s health or development.
In some genetic conditions with what is called recessive inheritance, people can have one non-working copy of the gene and still be healthy. These people are called carriers. For these diseases, think of the genes like two lights in a room. If you turn one light off, you can still see. Both if both lights are off, you can’t see the room any more. Because most carriers are healthy, they would never know that they are carriers.
Another type of single gene inheritance is called dominant. In dominant inherited diseases, having one non-working copy of a gene is enough to have the condition. Think of a bicycle. If a hole is punched in one bike tire, the bike isn’t going anywhere even if the other tire is working normally.
Rare chromosomal disorders
Genes themselves are located on chromosomes, which are inside our cells. Chromosomes contain all the genetic material that people get from their parents. Most people have 46 chromosomes or 23 pairs. The 23rd pair are called the sex chromosomes. Women usually have two X chromosomes, and men usually have one X and one Y chromosome.
If the sperm or eggs received unbalanced forms of chromosomes, meaning extra or missing pieces of chromosomes or entire chromosomes, the baby has a higher chance for birth defects or problems with development.
Sometimes there are variations in chromosomes themselves. For example, large chunks of genetic material may be missing or duplicated. In other people the amount of chromosomal material is typical, but the material is rearranged. Think of two sets of pens, one that is red and one that is blue. If you switched one blue cap and one red cap, you aren’t missing anything but they don’t look like everyone else’s. A large proportion of chromosomal variations are new in the person who has them, but some forms of chromosomal problems can be passed from one generation to the next.
There are some other forms of genetic diseases that are not covered here, but the above list gives you a good idea of some major categories.
How is genetic testing for inherited diseases used for people who are planning for pregnancy or already pregnant?
The idea of pursuing genetic testing can be overwhelming, but people do not have to figure it out on their own. A licensed genetic counselor has a master’s degree and is specially trained to review family medical background, assess the chances for inherited disease in a family, and suggest any follow-up, which sometimes includes genetic testing. However, genetic testing is not required, and talking with a genetic counselor does not mean someone will definitely have genetic testing. The genetic counselor is there to provide advice and guidance based on medical science and personal goals.
If people decide they are interested in genetic testing, the testing varies depending on the family’s medical background as well as their goals and questions.
Some routine testing is offered (but not required) during pregnancy but is not tailored to the prospective parents’ family medical background. Mainstream Genomics’ Free Information Guides provide some general information about genetic testing available before and during pregnancy.
To fine-tune genetic testing to a particular family, it may help to test family members, either the prospective parents themselves or sometimes even family members who have symptoms or features of inherited conditions. To get started, it is best to talk with a genetic counselor. Mainstream Genomics’ Family Screens are one way to connect with a qualified genetic counselor.
National Organization for Rare Diseases (NORD). https://rarediseases.org/
Ferriera, CR. The Burden of Rare Disease. AJMG 2018Chiu et al., 2018; Walker et al., 1.5–6.2% 2016