Abstract: Background：Risdiplam has showed efficacy in Chinsese children with different types of spinal muscular atrophy (SMA) for one-month treatment. However, there is still a lack of real-world data on long-term use of Risdiplam due to the low follow-up visit rates which may caused by the convenience of Risdiplam obtaining and other reasons. Objective：To observe the efficacy of Risdiplam monotherapy in children with different types of SMA treated for more than 12 months. Design：Case series report. Methods：Continuous cases with different types of SMA who were treated with Risdiplam as a monotherapy during the initial and follow-up periods from August 2021 to March 2023 in outpatient or hospital settings were enrolled. The enrolled cases with the age ≥ 16 days when the treatment was initiated were assessed by motor function scales at the beginning of the treatment and during their follow-ups. The oral dose of Risdiplam was calculated based on the patient's age and weight referred to the drug instructions. Patients were followed for at least 6 months and assessed by the qualified doctors with different motor scales. The outcomes of the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND)，the Revised Upper Limb Module Test (RULM)，the Hammersmith Functional Motor Scale Expanded (HFMSE) and the 6-Minute Walk Test (6MWT) were recorded. The adverse events (AEs) and the rate of AEs were reported. Main outcome measures：Improvement level of motor function score: last follow-up motor function score-baseline motor function score; or motor function score at the last follow-up after switching scales. Results：In total, 14 SMA pediatric patients were enrolled in this study, including 9 boys (64.3%) and 5 girls. Except for 1 presymptomatic patient, the median age of disease onset of the remaining 13 patients was 9.0 (3.0, 12.0) months; the median age of the 14 patients receiving Risdiplam treatment was 19.5 (6.5, 39.5) months. One patient had one copy number of SMN1 with a point mutation, and the remaining 13 patients occupied 0 copy of SMN1. The nubmer of atients with 1,2,3 and 4 copy numbers of SMN2 was 1,3,9 and 1, respectively. The case number of presymptomatic, type 1, type 2 and type 3 was 1,6,5 and 2, respectively. The interval between the last follow-up and the first drug administration was 20 (11.8, 25.5) months. The improvement in motor function reached clinical significance in 13 SMA patients , and the remained 1 patient also showed improved motor function score scale, but the improvement was not clinically significant. Nine patients had the results of blood routine, liver function and renal function at the baseline and during the follow-ups. The blood routine were normal. Two patients showed abnormal liver function at baseline but with normal results during the follow-ups, and some patients showed abnormal serum creatinine levels, which were caused by the SMA disease itself, and no increase in serum creatinine levels was found during follow-ups. Adverse events that may not be related to the treatment during follow-ups included 11 case of upper respiratory tract infection, 4 case of pneumonia, and 1 case of diarrhea. Except for pneumonia occurred in a child with type 2, the rest of the adverse events occurred in children with type 1. Adverse events that may be related to the treatment included skin color changes in 12 cases (85.7%), rash in 2 cases (14.3%), and constipation in 1 case (7.1%). No serious adverse reactions were found. This article reports one case who maintained normal motor function development after receiving Risdiplam treatment before symptom onset and one case who showed good efficacy of Risdiplam with one copy of SMN2. Conclusion：Long-term monotherapy of Risdiplam has shown good efficacy in Chinese children with different subtypes of SMA and the most common adverse drug reaction are respiratory tract infections and the change of skin color.

Key words: Spinal muscular atrophy, Risdiplam, Pre-symptomatic, One copy of SMN2, Children