Expanded Carrier Screening: New Guidance on Universal Testing
The American College of Obstetricians and Gynecologists (ACOG) has recently issued an opinion on the use of expanded carrier screening for genetic disorders.1 Lisa Blazejewski, Genetic Counselor, Quest Diagnostics, reviews the rationale for expanded screening and discusses its advantages compared to a traditional ethnicity-based approach.
Evolution from traditional to expanded screening
Traditional carrier screening is based on a person’s ethnicity. “Traditionally,” explains Ms. Blazejewski, “certain diseases are targeted for screening based on a patient’s ethnic background, taking into account the disease criteria for fetal, neonatal, or early childhood onset. A significant limitation of this approach is that we live in an increasingly multi-ethnic society, where patients are not necessarily aware of their complete ethnic make-up. In addition, the conditions we’re dealing with, while more prevalent in certain populations, are not limited to specific groups. So, taking an ethnicity-based approach really limits the amount of genetic information that a patient receives from that process.”
Recognizing the limitations of traditional carrier screening, a joint statement was issued in 2015 by professional groups providing guidance for the use of expanded carrier screening.2Moving from an ethnicity-based approach to one where screening is offered to all patients was seen as providing several benefits: overcoming inaccurate knowledge of ancestry in our increasingly multi-ethnic society; identifying the genetic conditions that do not occur solely in specific ethnic groups;ensuring universal coverage for patients of all ethnicities.2
“Combined with the desire to screen more people for more conditions was the recognition that technology now enables us to do this economically,” notes Ms. Blazejewski. “Next-generation sequencing, or high-throughput sequencing, actually made the concept of pan-ethnic screening feasible, because we can screen for up to several hundred conditions simultaneously at a similar cost as screening for a single condition. So now we are in a position to replace ethnicity-based screening that targets each gene and disease in a linear way with simultaneous screening for multiple diseases that can be offered to a broad population.”
Expanded screening panel
In March 2017 the American College of Obstetricians and Gynecologists’ Committee on Genetics published an Opinion Carrier Screening in the Age of Genomic Medicine.1This states that ethnicity-specific, pan-ethnic, and expanded-carrier screening strategies are all acceptable for pre-pregnancy and prenatal carrier screening and that healthcare providers should establish a consistent standard approach to be offered to each patient.
The number of conditions included in an expanded screening panel ranges from five to ten to several hundred.3Because of the potentially high number of conditions that may be included in an expanded carrier screening panel, ACOG recommends that the disorders selected for inclusion should meet several criteria, including:
· a carrier frequency of 1 in 100 or greater
· a well-defined phenotype
· a detrimental effect on quality of life
· possibility of diagnosis prenatally with opportunities for antenatal intervention
Based on the above criteria, the ACOG opinion provides an example of a carrier screening panel that includes 22 conditions.1The QHerit™ Expanded Carrier Screen is consistent with this example, providing a panel of 22 clinically relevant tests. “Performing a panel for gene mutations quickly and efficiently provides significant advantages for providers and patients,” says Ms. Blazejewski. “By offering a panel to all patients, a patient with a mixed ethnic background can undergo a test that would help find a mutation they wouldn't have realized they were at risk for carrying. The technology allows for all the testing to be done at the same time, which of course is important in the setting of pregnancies. The OB/GYN no longer needs to determine which diseases to screen for based on a patient’s ethnic background. Instead, the provider can simply tell patients that, if they would like to screen for diseases they may be at risk for passing on, there is now a panel available. They can present it as a single approach.”
Discussing findings with patients
An OB-GYN who is not familiar with genetic screening may be uncertain about how best to discuss findings with patients. Quest Diagnostics provides support for providers to help with such discussions. “Our team of genetic counselors is available to guide physicians on how to conduct discussions with patients about test results,” explains Ms. Blazejewski. “We can outline approaches for discussing the possible paths to take with their patients, such as partner testing, or fetal testing when both parents are carriers. We are able to provide clarification on our testing to the care team at any point in the process.”
- American College of Obstetricians and Gynecologists’ Committee on Genetics. Committee Opinion No. 690. Carrier screening in the age of genomic medicine. Obstet Gynecol. 2017:129:e35–40
- Edwards JG, Feldman G, Goldberg J, et al. Expanded carrier screening in reproductive medicine-points to consider: a joint statement of the American College of Medical Genetics and Genomics, American College of Obstetricians and Gynecologists, National Society of Genetic Counselors, Perinatal Quality Foundation, and Society for Maternal-Fetal Medicine. Obstet Gynecol. 2015:125(3):653-662.
- Haque IS, Lazarin GA, Kang HP, Evans EA, Goldberg JD, Wapner RJ. Modeled fetal risk of genetic diseases identified by expanded carrier screening. JAMA 2016;316:734–42.
Lisa Blazejewski, MS, CGC
Quest Diagnostics Inc.
Released on Thursday, September 21, 2017