The Critical Role of SMN1 Testing in SMA Prevention and Control: Kit Standardization and Clinical Practice

SMA Disease Burden and the Demand for SMN1 Testing

Spinal muscular atrophy (SMA) is one of the leading autosomal recessive genetic diseases causing infant mortality, with a population carrier frequency of approximately 1/50 to 1/40. Children with the severe form (Type I) often die before the age of two. Since deletion or mutation of the SMN1 gene is the root cause of SMA, accurate detection of SMN1 copy number is crucial for guiding genetic counseling, prenatal intervention, and early treatment. In recent years, with the market approval of disease-modifying therapies, SMA has transitioned from a fatal disease to a treatable one, and the demand for early genetic diagnosis has become increasingly urgent. The survival motor neuron 1 (SMN1) gene detection kit (fluorescence PCR melting curve method) has been gradually promoted in domestic screening programs due to its convenience and controllable cost.

Clinical Application Pathways of the Kit

The kit is primarily applied in clinical practice along three pathways: First, carrier screening. For individuals of reproductive age, especially couples with a family history of SMA or who have previously given birth to affected children, SMN1 copy number testing is recommended to determine carrier status. Second, prenatal diagnosis. If both partners are carriers, prenatal SMN1 gene testing of the fetus is required, commonly using chorionic villi or amniotic fluid samples, analyzed in parallel with the proband. Third, newborn screening. Some regions have incorporated SMA into newborn genetic disease screening programs, using dried blood spot samples for preliminary SMN1 gene screening, with positive cases requiring further confirmation. The fluorescence PCR melting curve method is suitable for batch testing in the above scenarios, with a single run capable of processing a 96-well plate or more samples.

Quality Control and Standardization Challenges in Testing

To ensure the clinical reliability of the kit, laboratories must complete performance verification before introduction. Routine verification items include precision, accuracy, limit of detection, cross-reactivity, and anti-interference capability. Due to the high homology of the SMN2 gene, positive interpretation must clearly distinguish the melting peaks of SMN1 and SMN2, generally requiring a melting temperature difference of at least 2°C. In addition, sample nucleic acid quality significantly affects results; it is recommended to use commercial nucleic acid extraction kits and to assess the integrity of the extracted products. For samples containing rare mutations or complex alleles, false negatives or copy number misjudgments may occur, and laboratories should establish a comparison mechanism with third-party methods, such as MLPA or long-range PCR. The result report should include SMN1 copy number, SMN2 copy number, and interpretation of clinical significance, along with a note on the detection method and its limitations.

Future Perspectives

With advances in SMA treatment approaches and the progression of medical insurance policies, the demand for SMN1 gene testing will continue to grow. The fluorescence PCR melting curve method is expected to be further optimized, for example, by introducing multiplex internal controls and digital PCR-assisted quantification technologies to enhance the detection capability for low-percentage mosaicism or microdeletions. Meanwhile, industry standardization efforts are accelerating, with consensus statements or technical specifications for guiding kit development, registration, and clinical application being successively issued. Laboratories should stay informed of subsequent updates to ensure that testing methodologies keep pace with the times and provide reliable technical support for SMA prevention and control.