By Dr. Brandon Colby MD, a medical expert specializing in genetic testing and personalized preventive medicine.
In this section of the Education Center, we've discussed what exactly is a genetic disease and what types of diseases can be detected through genetic testing. In this article, we'll discuss a very important type of genetic testing known as carrier screening.
What Is Carrier Screening?
Carrier screening is something that many people consider when they have a family history of a genetic disorder, such as cystic fibrosis. This screening can happen at any time, but the majority of people who have it performed do it before they decide to conceive, but it can be done at any time in a person's life. Understanding carrier screenings and their benefits can help people decide if it's something they should consider doing.
Genes, DNA, and Chromosomes
Genes are passed from each parent to a child. Genes are made up of cells that contain a substance called deoxyribonucleic acid, also known as DNA. DNA is made up of the chemicals Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). DNA strands wrap together to form chromosomes. There are 23 pairs of chromosomes in the human body for a total of 46. The pairs are made up of 23 chromosomes from the mother and 23 chromosomes from the father.
Characteristics and genetic diseases come from a single gene or combination of genes. The different combinations of genes are endless because there are 25,000 genes in the human body. This is why every single person is unique.
How Issues Occur
Genes hold information that helps the body function. The information comes from the mother and father. The mother and father's genes came from their mother and father, and so on and so forth.
Genetic disorders occur when a child receives a dominant gene (autosomal dominant gene) from one of the parents or two recessive genes that happen to pair up. Carrier testing can identify whether a dominant gene can cause an illness or if both parents have a recessive gene that could result in a genetic disease.
When someone has a gene mutation for a particular genetic disorder, that person is referred to as having carrier status. It doesn't mean the person is at increased risk of suffering from the disorder or if she/he has a child, he/she will suffer from that disorder even though recessive diseases can happen.
Learn More: What Is A Genetic Disease
What Is Carrier Screening?
Carrier screening is a term that refers to genetic testing on an individual who doesn't have a genetic disorder but may have a variant allele within a gene for a genetic condition.
Carrier screening should consist of whole-genome sequencing. This tests the entire genome to ensure all information is collected for analysis. Once the DNA test is performed and there is raw data to analyze, genetic counseling may be needed to interpret the analysis and provide information about what should be done to limit risk.
Learn More: Importance of Whole Genome Sequencing
Expanded Carrier Screening
Expanded carrier screening is a type of carrier screening that using a single sample and doesn't account for race or ethnicity. Companies offering expanded carrier screening devise their own list of genetic disorders they test for, which is called a screening panel. Some carrier screening panels are only focused on 100 disorders and may only consist of the most severe or rare diseases.
Carrier Screening Before Conceiving
The American College of Obstetricians and Gynecologists recommends in their article Carrier Screening in the Age of Genomic Medicine, "All patients who are considering pregnancy or are already pregnant, regardless of screening strategy and ethnicity, should be offered carrier screening for cystic fibrosis and spinal muscular atrophy, as well as a complete blood count and screening for thalassemias and hemoglobinopathies.
Fragile X premutation carrier screening is recommended for women with a family history of fragile X-related disorders or intellectual disability suggestive of fragile X syndrome, or women with a personal history of ovarian insufficiency. Additional screening also may be indicated based on family history or specific ethnicity."
Carrier screening should ideally be performed before pregnancy because couples learn about reproductive risks. It also gives them a chance to consider reproductive options, including if they should become pregnant and if they do if there are any preventive treatments for genetic disorders.
Obstetrics healthcare providers don't always discuss genetic carrier screening tests during family planning appointments unless there are concerns due to ethnic background (such as being of Ashkenazi Jewish descent), but it is important to consider them.
Conditions such as spinal muscular atrophy, sickle cell disease, and Tay-Sachs disease can seriously decrease an affected child's quality of life.
Preconception genetic testing can help parents plan preventive medicines to decrease the risk of their child suffering from debilitating medical issues, such as fragile x syndrome and so many others. Carrier screening panels can also help parents decrease the risks of disease even before they conceive.
Modern Day Carrier Screening
Most people who are thinking of conceiving decide not to seek carrier screening because they believe they need to consult with a genetic counselor or clinician. This is not true. With advancements in genomics technology, DNA analysis can be done from the comfort of people's homes.
With whole genome sequencing test results, raw data can be analyzed with an app that can check for a large number of genetic disorders. This can identify recessive disorders and when matched up with a partner can identify the possibility of the child suffering from a genetic disease.
Genetic testing for diseases is not reserved for people of a specific ethnicity, it should be performed on everyone. Insight into disease risk not only can save parents from worrying about the worst happening to their child but help a child avoid life-threatening birth defects and diseases.
If you're already pregnant, you may want to read the next article in our section on genetic testing for diseases: Genetic Testing During Pregnancy.
We've discussed what a genetic disease is and what types of diseases can be detected with a genetic test. So now you're interested in learning more about genetic testing! But there are many testing options and they can become overwhelming. Don't worry, in the next article we'll discuss your options and I'll explain how to choose a DNA test for diseases.
About The Author
Dr. Brandon Colby MD is a US physician specializing in the personalized prevention of disease through the use of genomic technologies. He's an expert in genetic testing, genetic analysis, and precision medicine. Dr. Colby is also the Founder of Sequencing.com and the author of Outsmart Your Genes.
Dr. Colby holds an MD from the Mount Sinai School of Medicine, an MBA from Stanford University's Graduate School of Business, and a degree in Genetics with Honors from the University of Michigan. He is an Affiliate Specialist of the American College of Medical Genetics and Genomics (ACMG), an Associate of the American College of Preventive Medicine (ACPM), and a member of the National Society of Genetic Counselors (NSGC).
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