A Single-Tube Nested PCR Method for SMN1 Deletion Detection in Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a rare autosomal recessive neuromuscular disorder caused predominantly by homozygous deletion of SMN1, resulting in degeneration of lower motor neurons and progressive muscle weakness and atrophy. In recent years, newborn screening programs for SMA using dried blood spots and PCR-based assays have been introduced in several countries, enabling presymptomatic diagnosis and earlier initiation of therapy. However, newborn screening does not eliminate the need for diagnostic testing in routine clinical practice, because adolescents and adults with milder or ambulant phenotypes may still present only after symptom onset and may experience diagnostic delay. We therefore developed a single-tube nested PCR (STNPCR) method as a practical diagnostic approach for symptomatic patients with suspected SMA. This method enables detection of homozygous SMN1 deletions using only standard PCR procedures and gel electrophoresis and may help identify patients with SMA who are not captured by newborn screening. Our assay using dried blood spot samples demonstrated preliminary technical feasibility in this proof-of-concept cohort, although further validation in larger independent cohorts will be required before its diagnostic utility can be established.