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Motor function was serially evaluated using the Hammersmith Functional Motor Scale Expanded (HFMSE), Revised Upper Limb Module (RULM), and Hammersmith Infant Neurological Exam Part 2 (HINE-2). Serum biomarkers, such as creatinine (Cr), creatine kinase (CK), and cystatin C, were measured at multiple time points. A linear mixed-effects model (adjusted for age, body mass index, SMA type, and treatment duration) was used to assess the biomarker\u2013function associations.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>Ambulant patients and those with four SMN2 copies demonstrated elevated CCR and Cr levels compared to non-ambulant patients and those with three SMN2 copies at baseline. Serum CCR levels were significantly higher than the baseline at V4\u2013V8 (10-26 months). Cr levels were significantly higher than the baseline at V8 (26 months), whereas CK and cystatin C levels remained unchanged. In the fully adjusted linear mixed-effects models, both CCR and Cr were positively associated with HFMSE and RULM scores. However, only CCR remained significant after adjustment. Cystatin C levels were inversely correlated with the HINE-2 scores.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>CCR is a promising biomarker in paediatric SMA patients receiving nusinersen monotherapy; however, its validity and generalizability require confirmation in larger, more diverse multicenter cohorts.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1186\/s12883-026-04657-3","type":"journal-article","created":{"date-parts":[[2026,1,24]],"date-time":"2026-01-24T13:44:03Z","timestamp":1769262243000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Serum creatinine to cystatin C ratio as a biomarker for monitoring motor-function in children with spinal muscular atrophy treated with nusinersen: a retrospective cohort study"],"prefix":"10.1186","volume":"26","author":[{"given":"Yuan yuan","family":"Zhang","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jie","family":"Wang","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Zhen qiong","family":"Cui","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kai","family":"Ma","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"297","published-online":{"date-parts":[[2026,1,24]]},"reference":[{"issue":"6","key":"4657_CR1","doi-asserted-by":"publisher","first-page":"885","DOI":"10.1016\/j.neuron.2005.12.001","volume":"48","author":"UR Monani","year":"2005","unstructured":"Monani UR. 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