PRS Embryo Testing: everything you need to know

Polygenic Risk Score (PRS) for embryo testing is a rapidly advancing technology in reproductive medicine.

It offers those using IVF the opportunity to assess the risk of complex genetic conditions in their embryos before implantation. However, this new technology comes with a range of considerations, both scientific and ethical.

As this technology has far-reaching implications, general public - and especially those considering using the technology - should have some knowledge, and understanding, about the technology and its broader consequences.

Here, we will break down the background, science, and what services private clinics in this area are currently offering.

Our hope is that this will lead to more informed decisions, and, ultimately, to using these technologies more responsibly.


What is IVF?

In Vitro Fertilization (IVF) is a process where eggs are retrieved from a woman's ovaries, fertilized by sperm in a laboratory, and then cultured into embryos. Once the embryos reach a certain stage, usually around five days (blastocyst stage), one or more embryos can be selected for transfer to the uterus in hopes of achieving a pregnancy.

While IVF was initially developed to help individuals or couples struggling with infertility, it has also become a gateway for genetic testing, allowing parents to screen embryos for certain conditions. As genetic testing technologies have advanced, so too have the opportunities to select embryos based on a range of health factors.

I Monogenic Testing in IVF

Monogenic testing, also known as Preimplantation Genetic Diagnosis (PGD) or Preimplantation Genetic Testing for Monogenic Disorders (PGT-M), is the process of screening embryos for specific single-gene disorders (monogenic disorders) such as:

  • Cystic Fibrosis

  • Tay-Sachs Disease

  • Huntington's Disease

  • Sickle Cell Anemia

These conditions are caused by mutations in a single gene, making them relatively straightforward to identify through genetic testing. PGT-M allows parents to avoid passing on severe inherited disorders by selecting embryos that do not carry the mutation.

This kind of testing is highly targeted. It’s typically used when parents know they are carriers of a specific gene mutation that causes disease. While monogenic testing can eliminate the risk of certain diseases, it does not assess the overall health of an embryo or predict complex diseases that may be influenced by multiple genes and environmental factors.

Polygenic Risk Scores (PRS)

Polygenic Risk Scores (PRS) are a more recent development in genetic testing. Unlike monogenic conditions, many common diseases (e.g., heart disease, diabetes, certain cancers) are influenced by multiple genetic variants, each of which contributes a small amount to the overall risk of disease. A PRS aggregates the effects of these variants to estimate the likelihood that an individual will develop a particular condition.

For example, a high PRS for Type 2 diabetes means an individual has a higher genetic predisposition to developing diabetes, but it doesn't guarantee they will get the disease. Environmental factors like diet and exercise play a significant role as well.

This type of scoring opens the door for broader genetic insights, but it's also more probabilistic, meaning it offers an estimate of risk rather than certainty.

PRS for Embryo Testing

PRS embryo testing applies the concept of polygenic risk scores to the embryos created during IVF. By analyzing the DNA from an embryo, scientists can calculate its risk for developing certain common, complex conditions later in life.

Potential conditions assessed through PRS include:

  • Heart disease

  • Diabetes

  • Certain cancers (e.g., breast, prostate)

  • Neurodevelopmental conditions (e.g., autism, ADHD)

The science and ethics of using PRS in embryo testing

This testing can also provide insights into non-disease traits like height or cognitive ability, raising significant ethical questions about its use for "designer babies." While PRS offers more information than monogenic testing, it comes with challenges:

  1. Probabilistic Nature: PRS only provides a risk estimate, meaning there's no guarantee an embryo with a low PRS will never develop a disease or that a high PRS will definitely lead to disease.

  2. Limited Scope: Current PRS only cover a limited number of traits and conditions. The predictive power is stronger for some diseases (e.g., heart disease) than others (e.g., mental health conditions).

  3. Ethical Considerations: The ability to select embryos based on risk scores for non-medical traits, such as intelligence, raises concerns about genetic equity and societal pressures.

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