Clinical profile of patients with spinal muscular atrophy at a neuromuscular disease reference center

Abstract

Background: Spinal Muscular Atrophy (SMA) is a rare genetic neuromuscular disease characterized by the degeneration of motor neurons in the spinal cord, leading to progressive proximal muscle weakness and atrophy. The disease presents a wide clinical spectrum with five phenotypes, with type 1 being the most severe and prevalent according to the literature. Objective: To describe the clinical profile of patients with SMA followed at a reference center for neuromuscular diseases. Methods: This was an observational, cross-sectional, and descriptive study based on the analysis of medical records and data extracted from the REDCap system between January 2023 and April 2025. The study population consisted of 50 patients with genetically confirmed SMA. Variables analyzed included sociodemographic, clinical (SMA subtype, age at symptom onset, maximum motor milestone achieved), and genetic data (number of SMN2 gene copies). Statistical analysis was descriptive, and data were summarized using SPSS software. Results: The sample was predominantly female (52%), with a median age of 12 years, and most patients self-identified as mixed-race (44%). Genetic analysis revealed that 92% of patients had a homozygous deletion of the SMN1 gene. The median age at symptom onset was 12 months, and the median age at diagnosis was 3 years. Regarding clinical characteristics, 54% of patients were able to walk independently at some point, while 42% were wheelchair dependent. The most frequent phenotype was type 3 SMA (46%), followed by type 2 (40%). The most common SMN2 copy number was three. Concerning treatment, 72% of patients had initiated some form of pharmacological intervention, with Nusinersen being the most frequently used therapy (52%). Conclusion: The study provided a detailed clinical profile of SMA patients. The findings are generally consistent with the literature, except for the predominance of milder forms of the disease (types 2 and 3). This inversion of the phenotypic profile suggests the presence of a survival bias, given the severity of type 1 and the prolonged diagnostic and therapeutic journey faced by patients. Furthermore, the high percentage of patients undergoing disease-modifying therapies highlights the importance of access to these interventions for clinical management and improved quality of life.