Pre-Pregnancy Genetic Testing: What Women and Doctors Need to Know
Is the child at risk of inheriting a genetic disease?
According to the Centers for Disease Control and Prevention (CDC), birth defects caused by genetic disorders affect 1 in every 33 births in the US (3%) each year and are the leading cause of infant death.
Global Genes reports that 24 million people in the US are living with rare diseases of genetic origin, and about 30% of children with a rare disease will not live to see their fifth birthdays.
With today’s advanced gene testing technology, women and their partners can find out if they are carriers for any one of hundreds of genetic disorders. Most inherited diseases are considered autosomal recessive fashion, which means that the child can only be affected if both parents have a gene mutation. If both carry a gene mutation, there’s a 1 in 4 chance their child will have that disease.
A recent news release from the American College of Medical Genetics and Genomics (ACMG) notes that “carrier screening for inherited genetic disorders is an important part of preconception and prenatal care for the nearly 4 million women who give birth in the US annually,” and that “new technology in genotyping and genetic sequencing allows for more efficient carrier screening of a greater number of conditions simultaneously.”
Doctor’s alert: people want to know more about their genes
In a new study of American adults’ knowledge of and attitudes toward genetic testing, 53% of the respondents wanted to know what’s in their DNA, and 70% wanted to find out if they could pass on a genetic disease.
Their doctors, however, do not seem to be on the same page, as only 7% of respondents said their physicians had discussed genetic screening with them.
Consumers are demanding more information and control over their health care, and new technology can now assess hundreds of mutations associated with genetic disease.
As Dr. Francis Collins, director of the National Institutes of Health, wrote in 2010:
“It is likely that within a few decades people will be puzzled and dismayed, as I am now, that our health care system put so many couples in an unnecessarily difficult position, by not identifying their carrier status until a pregnancy was already underway.”
The basics: how genetic testing works
Genetic tests use a sample of blood or saliva, which is usually collected at a physician’s office or a lab. The conditions the sample is screened for can depend on a person’s ethnic background, family history, previous pregnancies and the physician’s recommendations.
Everyone carries at least six changed genes, which could potentially cause a genetic disorder for a couple’s children, particularly if a partner is a carrier for the same genetic condition. Some diseases, such as Duchenne Muscular Dystrophy and Fragile X, are called X-linked conditions and are associated with mutation on the X chromosome.
Mothers who are carriers for an X-linked disorder have a 50% chance of passing the changed gene to each of their children. Because boys only have one copy of the X chromosome, which is inherited from their mother, they are usually severely affected.
Rarely, girls will have symptoms if they inherit the changed gene from their mothers, but usually they have no symptoms. Most people are carriers of at least one recessive or X-linked genetic condition.
Who should have carrier testing for genetic conditions?
Carrier testing for genetic conditions is available to all reproductive age women and their partners. Persons are at higher risk of being a carrier if anyone in their family has had a genetic disease or if they belong to certain ethnic groups. For example, the following groups face increased risks for these diseases:
Certain groups may benefit more from genetic testing, as they face increased risks.
- European Caucasians (cystic fibrosis)
- Eastern European Jews (cystic fibrosis, Tay-Sachs, Canavan and familial dysautonomia)
- Black people and people of Mediterranean descent (sickle cell anemia and thalassemia)
- People of Southeast Asian (thalassemia)
- French Canadians (Tay-Sachs and cystic fibrosis).
Updated guidelines from The American Congress of Obstetricians and Gynecologists (ACOG) Committee on Genetics state that “it is reasonable to offer cystic fibrosis carrier screening to all patients.” The American College of Medical Genetics and Genomics also issued practice guidelines recommending that testing for spinal muscular atrophy be offered to all couples, regardless of race or ethnicity.
Newer tests, called expanded genetic carrier screenings, can detect gene mutations for Fragile X syndrome and many other rare disorders. For example, Horizon from Natera screens for up to 274 autosomal recessive and X-linked genetic conditions and generally provides the results in 10-14 business days.
Benefits of pre-pregnancy testing
Genetic carrier screening gives women and their partners valuable information to make the reproductive choices that are right for them and their families. If the results are negative, they can be reassured that the chance that their children will be born with the disorders they were screened for is extremely small.
And if a couple is at risk of having a baby with a recessive disease, they can consider various options, such as:
- Natural pregnancy with or without prenatal diagnosis, such as chorionic villus sampling (CVS) or amniocentesis
- Preimplantation genetic diagnosis (PGD) with in vitro fertilization (IVF) to test and then transfer embryos free of the disease that both partners carry
- Use of a sperm or egg donor.
In addition, having this knowledge before a pregnancy gives a couple enough time to learn about and prepare for having a baby that may have a specific genetic condition. The test information could also help other prospective parents in their families know that they, too, could be carriers and might benefit from a screening test.
A team effort
Unfortunately, most people do not realize they have potentially disease-carrying genes until their children are affected. Women and their partners also may want to talk to a genetic counselor, whom they can find through the National Society of Genetic Counselors or the American Board of Genetic Counseling.
The test described has been developed, and its performance characteristics determined by the CLIA-certified laboratory performing the test. However, it has not been cleared or approved by the US Food and Drug Administration (FDA).
Although the FDA do not currently clear or approve laboratory-developed tests in the US, certification of the laboratory is required under CLIA to ensure the quality and validity of the tests.
For more information on genetic and prenatal tests, please go to Natera’s website.