Genetic Carrier Screening: What You Need to Know
Our DNA contains two copies of each gene — one inherited from one’s mother, and one from one’s father. While these genes pass along family characteristics like hair- and eye color, they also may pass on inherited conditions. Such inherited conditions are caused by mutations, or changes in the genes, and as long as only one copy of the gene contains a mutation there are usually no associated symptoms.
Historically, genetic carrier screening for select disorders has been offered to patients of certain ethnic groups or has been limited to a few conditions, e.g., cystic fibrosis, spinal muscular atrophy and fragile-X, and this is still the approach offered by many reproductive specialists. However, for several years at the Center for Reproductive Medicine (CRM) we have recommended expanded genetic carrier screening (ECS) for all patients due to the fact that of the 176 conditions for which we screen, most people carry at least one mutation. Usually this only becomes an issue if both patient and partner have a mutation in one copy of the same gene. In this situation, even though neither has any symptoms, there is a 1 in 4 chance for each pregnancy that a child will be affected by the condition associated with the gene (autosomal recessive disorders). While some of these autosomal recessive diseases are relatively benign, others are life-threatening. In addition, there are a few conditions where only the mother needs to carry a mutation for her children to be at risk (X-linked genetic disorders).
The ideal time to assess genetic carrier status is prior to conception so that all reproductive options may be considered. These options would include preimplantation genetic diagnosis, where a few cells from a day-5 embryo may be biopsied and used for diagnosis, or usage of donor eggs or donor sperm.
If one decides upon ECS, as opposed to ethnicity-based screening, there must be appropriate counseling as to the pros and cons as well as to the limitations of testing. There should also be the willingness for one’s partner to be tested if there are one or more mutations identified. Further, there should be the provision for posttest counseling, including comprehensive consultation with genetic counselors.
Due to recent advances in throughput and lowered costs, ECS has become a valid option over traditional limited or ethnic screening and there is a progressively increasing screening panel for increasingly rare disorders. Such technological strides must be seen in context, however, and may be a double-edged sword.