Parents-to-be may consider using preimplantation genetic testing (PGT) to screen embryos for inherited genetic diseases, but PGT for single gene disorders has its limitations and cannot detect every possible condition.
Here, we explore the future of PGT, and how science and technology are rapidly co-evolving to change how diseases are detected and treated at the earliest stage of life.
Limitations of PGT
Some diseases are complex and require variations in several genes, as well as lifestyle and environmental factors. These conditions include diabetes, some forms of heart disease and Alzheimer’s disease. Unfortunately, PGT cannot effectively test for those conditions.
Most preventable genetic diseases via PGT, such as cystic fibrosis or hereditary cancer syndromes, are definitively linked to variants of a single gene. Heart disease, depression and diabetes, on the other hand, have much more complex causes, often involving multiple genes and external factors, such as lifestyle or environmental triggers.
Multifactorial or complex disorders may appear in family histories, but since there is no single genetic factor, no current techniques can be used to prevent them, according to the U.S. National Library of Medicine.
Using the latest PGT methods, embryos can simultaneously be screened for a variety of single-gene disorders and chromosomal abnormalities — which are also common causes of genetic conditions — with a high degree of accuracy. However, despite significant technological advances, PGT, like all medical procedures, is not infallible. Because there is a small chance PGT will fail, parents who know that they’re carriers of genetic diseases can also undergo prenatal testing to ensure a positive outcome, Mayo Clinic notes.
Technological Advances and PGT
PGT depends on fields of science that are swiftly advancing, so this technique is likely to improve.
Currently, PGT for single gene disorders only typically involves examining a small region of the embryo’s genome thought to house a harmful genetic variant. Since the price of whole genome sequencing is falling dramatically, per Illumina.com, researchers will someday be able to test the genome more widely as part of PGT.
Sequencing an embryo’s entire genome would allow doctors to discover disease markers that a lower resolution method could miss; it could also identify genetic problems in an embryo without prior knowledge of a specific risk to children based on genetic testing or family history.
Inherited Mitochondrial Disorders
Another area in which PGT could see improvements is its use in preventing inherited mitochondrial disorders. Mitochondria are the parts of our cells that produce energy and have their own DNA, which can also contain variants that cause severe medical problems, according to the United Mitochondrial Disease Foundation.
All mitochondria in an embryo come from the egg, so if a mitochondrial disorder runs on the mother’s side of the family, a couple may want to seek genetic counseling. So far, PGT’s use in preventing problems linked to mitochondrial DNA remains experimental, but researchers are currently investigating whether the technique could be improved.
PGT could also be adapted in the future through the use of genome editing.
Researchers are studying whether genome editing tools, like CRISPR, could safely be used to alter human embryos. Although genome editing is controversial, it wouldn’t change traits influenced by certain genes and their interplay with the environment, such as intelligence. Instead, genome editing is suited to repair specific genetic problems by cutting out the faulty version of the gene, Time reported in August 2017.
CRISPR has the potential to revolutionize reproductive medicine, but it is still in its developmental stage. IVF and PGT are currently the most reliable ways to screen embryos for genetic diseases, added Time.
Future Developments for PGT
The future of PGT lies in further genetic research. As scientists continue to discover the exact genetic causes of hereditary medical problems, it will become possible to screen for more conditions. Research isn’t slowing down, and the number of preventable genetic diseases that PGT can detect will only increase in years to come.
Dawn Michelle Lipscomb, PhD, is a biophysicist, podcast host, and science writer. While finishing a dual B.S. in Physics and Biology at UT San Antonio, she published research on planetary biosignatures for space exploration at NASA-JPL and designed THz bioeffects experiments for human tissues at the Air Force Research Laboratory. In 2017, she completed her Biophysics doctorate at UC Berkeley by developing a new method for imaging proteins that regulate gene expression using cryo-electron microscopy. Today, she co-hosts a live video podcast series on regenerative medicine and writes articles about groundbreaking research in aging and genetics.