1 in 59 women in region of China found to be SMA carrier: Study

Carrier screening results will help scientists develop prevention strategies

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by Andrea Lobo |

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Among women of reproductive age in a southern region of China, one in every 59 tested in a screening program was found to be a carrier of mutations in the SMN1 gene — the main cause of spinal muscular atrophy (SMA) — a new study reports.

In the southern China city of Shenzhen, researchers were seeking to better understand how to implement SMA screening procedures. In hospital testing of nearly 23,000 women with fertility issues, an SMA carrier screening found that more than 350 had an SMN1 gene mutation.

SMA only develops if disease-causing mutations are present in both copies of a person’s gene — one inherited from each biological parent. Being a carrier means that an individual has mutations in only one copy of the SMN1 gene, together with a healthy copy. This means that the SMA carrier will not develop the disease, but can pass the mutation to any biological children.

Their findings, the researchers said, “will help us to better formulate the prevention and management strategies and programs for SMA.”

“We … acquired the shortcomings and problems in our current SMA screening program,” the team added.

The study, “Carrier screening for spinal muscular atrophy in 22913 Chinese reproductive age women,” was published in Molecular Genetics & Genomic Medicine.

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SMA is a rare genetic condition usually caused by inherited mutations in the SMN1 gene that lead to the progressive loss of motor neurons, the specialized nerve cells that control voluntary movements. This ultimately results in the disease symptoms, such as muscle weakness and atrophy, or difficulties breathing, speaking, and swallowing.

The main disease-causing mutations in SMA are inherited in an autosomal recessive manner, meaning that the condition will only develop if disease-causing mutations are present in both copies of the SMN1 gene. While an SMA carrier — who has a mutation in only one copy of the SMN1 gene — will not develop the disease, that individual can pass along the mutation to any offspring, who could develop the condition if the other parent also is a carrier.

It is estimated that in the general population, about one in every 50 people is a carrier and about one in every 6,000 to 10,000 children is born with the disease.

Considering the disease severity, high mortality rate, and feasible detection techniques, it is suggested that routine carrier screening should be available to all women who are pregnant or considering pregnancy, or even for the general population.

However, “large-scale data about the SMA carrier screening was still lacking in China except some regions. Therefore, how to comprehensively and efficiently carry out pregnancy/prenatal SMA carrier screening is extremely urgent,” the researchers wrote.

To that end, a three-stage screening procedure for SMA was adopted at the Affiliated Shenzhen Maternity & Child Healthcare Hospital between September 2019 and December 2022.

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Over 350 of nearly 23,000 women found to have SMN1 mutations

Over a little more than three years, the team performed SMA carrier screenings on 22,913 women with fertility issues and no family history of SMA who sought treatment at the hospital. Most of the women ranged in age from 26 to 40, and almost half (46.6%) were pregnant.

Via screening, a total of 389 women tested were found to be SMA carriers, corresponding to 1.7% or a prevalence of one in every 59 individuals.

When a woman was identified as a carrier, her partner also was recommended for screening. In all, 242 or 62% of these women’s partners were tested. Eight were also found to be carriers.

These dual-carrier couples were advised that they had a 25% chance of having a child with SMA. A prenatal diagnosis was performed in six couples; two did not have testing due to abortion or not being pregnant.

The diagnosis involved collecting a sample of amniotic fluid – the fluid that surrounds and protects the fetus – which can be used to diagnose genetic disorders. The procedure was performed between 16 and 24 weeks into the pregnancy, or from about four months to six months of gestation.

Two fetuses were determined to have SMA, with mutations in both SMN1 gene copies.

Although the acceptability and awareness of SMA carrier screening in Chinese population has increased in recent years, it still fails to reach the ideal expectation. … Our experience may … facilitate the popularization of SMA carrier screening [in this country region].

Overall, the researchers noted that the percentage of women in Asia, and specifically in China, who request SMA carrier screening is “much lower” than in other regions of the world. The team noted that “about 98.7% of the population accepted carrier screening for SMA in the United States … and 93% of women in Israel requested the SMA carrier test.”

Their goal, they said, was “to increase the acceptability of screening in the population” in China, and particularly in the southern regions of the country.

“Although the acceptability and awareness of SMA carrier screening in Chinese population has increased in recent years, it still fails to reach the ideal expectation,” the researchers wrote.

“Our experience may provide a basis for and facilitate the popularization of SMA carrier screening [in this country region],” they concluded.