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Summary: Background: Real-world data on gene addition therapy (GAT) with onasemnogene abeparvovec (OA), including all age groups and with or without symptoms of the disease before treatment are needed to provide families with evidence-based advice and realistic therapeutic goals. Aim of this study is therefore a population-based analysis of all patients with SMA treated with OA across Germany, Austria and Switzerland (D-A-CH). Methods: This observational study included individuals with Spinal Muscular Atrophy (SMA) treated with OA in 29 specialized neuromuscular centers in the D-A-CH-region. A standardized data set including WHO gross motor milestones, SMA validated motor assessments, need for nutritional and respiratory support, and adverse events was collected using the SMArtCARE registry and the Swiss-Reg-NMD. Outcome data were analyzed using a prespecified statistical analysis plan including potential predictors such as age at GAT, SMN2 copy number, past treatment, and symptom status. Findings: 343 individuals with SMA (46% male, 54% female) with a mean age at OA of 14.0 months (range 0–90, IQR 20.0 months) were included in the analysis. 79 (23%) patients were clinically presymptomatic at the time of treatment. 172 (50%) patients received SMN2 splice-modifying drugs prior to GAT (risdiplam: n = 16, nusinersen: n = 154, both: n = 2). Functional motor improvement correlated with lower age at GAT, with the best motor outcome in those younger than 6 weeks, carrying 3 SMN2 copies, and being clinically presymptomatic at time of treatment. The likelihood of requiring ventilation or nutritional support showed a significantly increase with older age at the time of GAT and remained stable thereafter. Pre-treatment had no effect on disease trajectories. Liver-related adverse events occurred significantly less frequently up to 8 months of age. All other adverse events showed an even distribution across all age and weight groups. Interpretation: Overall, motor, respiratory, and nutritional outcome were dependent on timing of GAT and initial symptom status. It was best in presymptomatic children treated within the first six weeks of life, but functional motor scores also increased significantly after treatment in all age groups up to 24 months. Additionally, OA was best tolerated when administered at a young age. Our study therefore highlights the need for SMA newborn screening and immediate treatment to achieve the best possible benefit-risk ratio. Funding: The SMArtCARE and Swiss-Reg-NMD registries are funded by different sources (see acknowledgements).

Metformin (N,N-dimethylguanylguanidine) is one of the most prescribed drugs with pleiotropic, exerted in part by not fully elucidated mechanisms of action. We developed and validated a gas chromatography–mass spectrometry (GC–MS) method for the quantitative analysis of metformin (metformin-d0) in 10-µL aliquots of human serum and urine using N,N-[dimethylo-2H6]guanylguanidine (metformin-d6) as the internal standard. The method involves evaporation of the samples to dryness, derivatization with pentafluoropropionic (PFP) anhydride in ethyl acetate (30 min, 65 °C), and extraction into toluene. The negative-ion chemical ionization GC–MS spectra of the PFP derivatives contain a single intense ion with mass-to-charge (m/z) ratios of m/z 383 for metformin-d0 and m/z 389 for metformin-d6. Our results suggest that all amine/imine groups of metformin-d0 and metformin-d6 are converted to their N,N,N-tripentafluoropropionyl derivatives, which cyclize to form a symmetric triazine derivative, of which the non-ring amine group is amidated. Quantification was performed by selected-ion monitoring (SIM) of m/z 383 and m/z 389. Upon validation, the method was applied to determine serum and urine metformin concentrations in 19 patients with Becker muscular dystrophy (BMD). Serum and urine samples were collected at baseline (Visit I), after six weeks of supplementation (Visit II) with metformin (3 × 500 mg/d; metformin group; n = 10) or l-citrulline (3 × 1500 mg/d; citrulline group; n = 9) followed by a six-week supplementation with 3 × 500 mg/d of metformin plus 3 × 1500 mg/d l-citrulline. At Visit I, the metformin concentration in the serum and urine was very low in both groups. The metformin concentrations in the serum and urine of the patients who first took metformin (MET group) were higher at Visit II and Visit III. The metformin concentration in the serum and urine samples of the patients who first took l-citrulline (CITR group) were higher at Visit III. The serum and urine concentrations of metformin were insignificantly lower in the CITR group at Visit III. The mean fractional excretion (FE) rate of metformin was 307% (Visit II) and 322% (Visit III) in the MET group, and 290% in the CITR group (Visit III). This observation suggests the accumulation of metformin in the kidney and its secretion in the urine. The GC–MS is suitable to measure reliably circulating and excretory metformin in clinical settings.