Study in China supports carrier screening program for SMA
Data show 1 in 69 people in southern China carry disease-causing mutation
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The successful implementation of a spinal muscular atrophy (SMA) carrier screening program in southern China shows the “feasibility and clinical utility” of such a program in the country, researchers said.
The program tested thousands of people, allowing couples at high risk of having a child with SMA to be identified and receive appropriate guidance. Data showed that roughly 1 in 69 people in southern China are carriers for SMA.
The scientists called for SMA carrier screening to be made widely available to prospective parents in China. “These results support the expansion of SMA carrier screening as a standard component of preconception and prenatal care throughout China, offering an evidence-based approach to reducing the burden of this devastating genetic disorder,” they wrote.
The study, “Integrating LNA-qPCR and full-length SMN1 sequencing for precision SMA carrier screening: large-scale validation in 30,849 individuals,” was published in Clinica Chimica Acta.
“Our findings provide critical epidemiological data and validate a cost-effective screening methodology suitable for population-level implementation,” the researchers wrote.
Most carriers unaware
SMA is caused primarily by mutations in the SMN1 gene. A mutation known as the exon 7 deletion, in which a section of the gene is missing, accounts for the vast majority of cases.
Everyone inherits two copies of the SMN1 gene, one from each biological parent. SMA only develops if both copies of the gene carry a mutation. People who have one mutated SMN1 copy and one healthy copy are known as SMA carriers. Carriers will not develop symptoms of SMA, but they can pass the mutated gene on to their biological children. If two SMA carriers reproduce, there is a 1 in 4 chance that their child will have SMA.
Most people who are SMA carriers don’t know it. Carrier screening, in which prospective parents are routinely tested for SMN1 gene copies, may help inform reproductive choices.
“The primary aim of carrier screening is to assess the risk of having affected offspring among asymptomatic carrier couples without a known family history,” the researchers wrote.
The SMA carrier screening program tested more than 30,000 people across 14 cities in Hunan Province. The study included couples who were either hoping to get pregnant or were in the early stages of pregnancy.
Of the 30,733 participants in the study, 438 were SMA carriers. That works out to a rate of about 1.43%, or 1 out of every 69 people. The researchers noted that carrier prevalence varied from city to city.
In the main screening program, female participants would first be tested for exon 7 deletion. If the female participant was positive, their male partner would then also be tested. This identified five couples where both the prospective mother and father were SMA carriers, unbeknownst to either of them. These couples were able to receive comprehensive counseling, including the option for testing before pregnancy to avoid implanting an embryo with SMA.
The program also tested 58 couples who were at high risk because they already had children with SMA or were suspected of having the disease. Testing showed that all but one of these individuals carried an exon 7 deletion in both SMN1 gene copies. In the sole outlier, sequencing of the SMN1 gene revealed a different mutation known to cause SMA, called c.22dupA.
Most of the high-risk couples were pregnant at the time of testing, and testing revealed that 16 of the fetuses had SMA. In each of those cases, the family chose to terminate the pregnancy after receiving counseling.
“The successful prevention of 16 affected births through prenatal diagnosis demonstrate the substantial impact of comprehensive genetic screening programs,” the researchers wrote.
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