A large-scale study analyzing genetic screening for biomarkers associated with spinal muscular atrophy (SMA), cystic fibrosis (CF), and fragile X syndrome (FXS) adds new insights on the incidence of these genetic markers.
The study, published in the journal Genetics in Medicine, also highlights the importance of using genetic screening as a tool to better inform prenatal and newborn decision-making.
The use of genetic tests to identify individuals who may be at risk of developing disorders caused by genetic abnormalities has been widely debated. These tests may inform patients if they are carriers of a genetic disease-associated biomarker, and what the risk is of passing it on to their descendants.
Results of a survey to the SMA community showed that about 70-80 percent of patients and family members are in favor of preconception, prenatal, and newborn genetic screening. Many of them believed that such tests are important for informed decision-making, early treatment, and to promote SMA awareness. However, there are still many ethical and social concerns on this matter.
Advances in genetic screening technology have made it possible to extend the analysis to several recessive and chromosome X-linked medical conditions at the same time. The question remains which conditions should be included in the testing panels.
Since 2012, Victorian Clinical Genetics Services (VCGS) in Australia has offered the prepair multidisorder genetic carrier screening test for the presence of genetic biomarkers for SMA, CF, and FXS, combined with supportive care through genetic counseling consultations.
In the study titled “Reproductive genetic carrier screening for cystic fibrosis, fragile X syndrome, and spinal muscular atrophy in Australia: outcomes of 12,000 tests,” a team of researchers led by Alison Archibald, PhD, associate genetic counselor at VCGS, presented an analysis of the first 12,000 individual tests conducted with prepair.
They found that one in every 20 patients screened were carriers of a genetic disease-associated biomarker: 241 patients had SMA biomarkers, 342 patients had CF biomarkers, and 35 had FXS genetic markers. About 88 percent of these carriers had no prior family history of any of these conditions.
According to the pre-established protocol, 94.68 percent of SMA and CF carriers’ partners were also tested. The secondary testing showed that 0.42 percent of the couples, representing 1 in 240, were at high risk of having a child with one of the conditions.
Only one couple was identified with increased risk for SMA, and the woman was already pregnant at the time the screens were conducted. So they decided to undergo prenatal diagnosis, which confirmed the SMA diagnosis for the fetus. The test revealed the presence of two copies of SMN2 biomarker, indicating a high risk for an early-onset form of SMA. The couple decided to terminate the pregnancy.
“This genetic carrier screening program for CF, FXS, and SMA has proven to be successful in identifying individuals and couples at increased risk of having a child affected by one of these conditions,” the researchers wrote.
The researchers believe that screening programs combining laboratory services with genetic counseling support are essential to ensure that the patient receives the needed support to make informed reproductive choices.
“This program has demonstrated that despite individual recessive conditions being relatively rare, when tested collectively, the combined chance of an affected child with one of the conditions is comparable to that of Down syndrome,” they wrote.
Overall, the study demonstrates that screening programs similar to this can provide reliable information with diagnostic value. In addition, it supports the expansion of the screening panels to other recessive conditions that may benefit from such a strategy.