“It’s not so bad to find out that you are a carrier…[but] finding out that you are a carrier of SMA [spinal muscular atrophy] from your child dying is the wrong way to do it.”
-Deborah Heine, executive director of the Claire Altman Heine Foundation
Like many parents of children with rare genetic diseases, Deborah and her husband learned of their positive carrier status only after their daughter Claire was diagnosed with SMA. The couple had already given birth to one healthy child. In planning their second pregnancy, they underwent genetic screening for conditions like cystic fibrosis and Tay-Sachs. Carrier screening for additional disorders was available but not offered because there was no suspicious family history. A few months into life, Claire was diagnosed with a fatal condition.
The fact is most children with rare genetic diseases are born to families with absolutely no history of the condition. As many as one out of five individuals is thought to be a “carrier” of a rare recessive genetic condition. A carrier does not typically manifest symptoms or have a family history of the disease. When two carriers of the same recessive gene begin a family together, they can give birth to an affected child. Prospective parents are mostly unaware of their carrier status prior to planning a family.
In the United States, screening for a small list of diseases is typically initiated at the first prenatal visit, after a pregnancy is confirmed. At this stage, if there is no notable family history, screening recommendations are guided by ethnic prevalence: Caucasians and Hispanics are offered cystic fibrosis; African Americans are offered sickle cell; Ashkenazi Jews are offered Tay-Sachs at a minimum. All pregnant women are offered screening for Down syndrome; yet, rare recessive diseases are collectively present in 1/280 births, which is more common than Down syndrome.
Comparatively, several countries around the world practice preconception screening, including Israel, Cyprus and Taiwan. The UK has recently taken steps towards introducing carrier screening at the high school level. The idea is that knowledge of reproductive risks prior to family planning allows couples to take advantage of all of their options. At-risk couples may choose in-vitro fertilization (IVF) with preimplantation genetic diagnosis (PGD). Others consider prenatal diagnosis in the early stages of their pregnancy. Still, some use the information to prepare for the birth of a child with special needs or consider adoption. The way in which the information is digested is very personal. Limiting access to this information, however, deprives families of the right to make informed decisions.
Cost has been cited as the main barrier to routinely offering screening for rare diseases. At several hundred dollars per disease, the expense of testing everyone for multiple conditions adds up quickly. This was true until recently. Using advances in genomic technology, scientists have made possible an affordable pan-ethnic genetic screen for over 100 recessive genetic diseases. The price — just under $400— compares to the current cost of screening for only one rare disease. With vast amounts of information available at an affordable cost, justifying the omission of diseases from routine screening proves difficult.
The field of genetics is moving at an extremely rapid pace, and carrier screening is just the beginning. As the cost of genomic technology continues to decline, access to information about all of our genes will increase. In the era of modern medicine, waiting until a child is born with a rare inherited disease to offer carrier screening is simply unacceptable. In his recent book, Dr. Francis Collins, Director of the NIH, notes, “…within a few decades people will look back on our current circumstance with a sense of disbelief that we screened for so few conditions…they will also be puzzled and dismayed, as I am now, that our health care system put so many couples in an unnecessarily difficult position, by not identifying their carrier status until a pregnancy was already underway.”
Shivani B. Nazareth is RARE Blog contributor and a board-certified genetic counselor with Counsyl, Inc. For more information about carrier screening for rare disorders, visit www.counsyl.com.