Preconception and Prenatal Genetic Counseling

Carrier screening is a type of genetic test designed to help couples understand their risk of having a child with a genetic disorder.  

Dr. Bassetti offers the following overview. “Each of us has 2 copies of most genes: one inherited from our mother and one from our father. For disorders inherited in an autosomal recessive manner, a person must have a disease-causing variant (“mistake” or “misspelling”) in each copy of the gene in order to manifest the condition. This most commonly occurs when both of the individual’s parents is a carrier of that condition. A carrier means that you have one normal copy of the gene and one copy harboring a disease-causing variant. 

“When both parents are carriers of the same genetic variant, they’ll have a 25 percent chance of having a child with the associated disorder,” she continues. 

What are some examples of autosomal recessive disorders?  

A well-known example is cystic fibrosis (CF)—a serious respiratory disease that is one of the most common inherited genetic disorders among people of European descent: roughly 1 in 2,500 to 3,500 births.  

Another example is Tay-Sachs disease, which, in its most severe form, is fatal after just a few years of life. Couples of Ashkenazi Jewish ancestry, among several other ethnic groups, are at higher risk to be carriers of Tay Sachs disease and are advised to undergo carrier screening—preferably before conception or in early pregnancy. That will afford them the chance to make the best possible decisions about their reproductive future, with the help of a genetic counselor. 

• Will they decide to pursue in vitro fertilization (IVF) at some point?  
• If pregnant, will they decide to continue with the pregnancy?  
• How can they best plan for delivery of a child with a genetic disorder?  

These are the types of questions a couple may bring to a counseling session. 

“Screening for Tay-Sachs among at-risk populations has decreased the prevalence of that disease,” Dr. Bassetti says. “That’s an important benefit of genetic screening and counseling.” 

Beyond these well-known autosomal recessive genetic disorders, are there other types of inherited disorders? 

X-linked conditions 

There are many X-linked disorders, caused by variants in genes that are located on the X chromosome, one of the two sex chromosomes (X and Y). Female carriers of an X-linked condition, having two X chromosomes (XX), typically have a gene on one X chromosome with a disease-causing variant and a normal copy of the gene on the second X chromosome. As a result, female carriers of X-linked conditions usually do not show symptoms or may exhibit only mild symptoms. However, they have an increased risk of passing the condition to their sons, as males have only one X chromosome (XY). If a male inherits the disease-causing variant, there is no second X chromosome to compensate, leading to the development of the condition. 

One example is Fragile X syndrome, the most common inherited form of intellectual disability, which primarily affects males. “It is recommended that prospective mothers be screened for Fragile X syndrome, ideally before conception or early in pregnancy,” she says.  

Autosomal dominant disorders 

Then, there are autosomal dominant disorders, she explains. These require just one copy of a gene to harbor a disease-causing variant and cause the associated disease. When a parent has an autosomal dominant condition, there is a 50 percent chance that the child will inherit the disorder. While these variants are associated with individually rare diseases, such as Marfan syndrome, Huntington’s disease and neurofibromatosis, collectively they affect about 1 in 200 individuals. 

In fact, rare disease is not all that rare! According to the National Institutes of Health (NIH), there are approximately 10,000 rare genetic diseases affecting 20 to 30 million people in the United States. That’s 1 in 10 Americans. But each of these diseases affects a small number of people, which is why screening has remained limited for most of them. But with advanced screening technology, that’s beginning to change. 

How are genetic tests performed? 

Preconception/prenatal carrier screening and most other prenatal screening tests involve a simple blood draw, saliva sample or cheek swab.  

Diagnostic testing may require more elaborate techniques to determine if the fetus has a genetic or chromosomal disorder. Samples for testing are obtained from chorionic villus sampling (CVS) or amniocentesis.  

Chorionic villus sampling (CVS) involves taking a small sample of cells from the placenta.  Amniocentesis entails taking a sample of amniotic fluid from the sac surrounding the fetus.  Each approach has its own benefits and limitations, which can be reviewed in detail with Weill Cornell’s prenatal genetic counselors to help determine the best option for the patient. 

Is genetic counseling covered by insurance? 

Most insurance plans will cover a consultation with a genetics provider (genetic counselor or MD geneticist). Some plans may fully cover the visit, while others may require co-payments, deductibles or other out-of-pocket expenses. Typically, insurance plans cover testing related to a specific medical condition, or if it is considered medically necessary. “Our office staff will work with your insurance company to seek authorization,” Dr. Bassetti says. 

Weill Cornell Medicine has been named a Center of Excellence by the National Organization for Rare Diseases (NORD) 

About a year ago, Weill Cornell Medicine was designated a NORD Center of Excellence, with Dr. Omar Abdul-Rahman serving as its director. “Rare diseases don’t always get the attention they should,” Dr. Bassetti says, “but with this recent designation, we’re now part of a network of specialists who share information and improvements in patient care.  

“As a NORD Center of Excellence, our clinical geneticists can participate in working groups,” she adds. She’s on the NORD committee for medical education. That means she can identify medical students interested in genetics, mentor them and encourage them to pursue that specialty; a specialty that is increasingly coming into its own, marked by advances in gene therapy and other treatment options for genetic diseases. 

If you or your partner has a family history of an inherited disorder, if you’ve experienced several miscarriages, or if you’d simply like to be assessed for your risk of conceiving a child who may be born with a genetic disorder, reach out to a member of Weill Cornell’s medical genetics team.