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Background and purpose The therapeutic landscape of spinal muscular atrophy (SMA) has changed dramatically during the past 4 years, but treatment responses differ remarkably between individuals, and therapeutic decision‐making remains challenging, underlining the persistent need for validated biomarkers. Methods We applied untargeted proteomic analyses to determine biomarkers in cerebrospinal fluid (CSF) samples of SMA patients under treatment with nusinersen. Identified candidate proteins were validated in CSF samples of SMA patients by Western blot and enzyme‐linked immunosorbent assay. Furthermore, levels of peripheral neurofilament heavy and light chain were determined. Results Untargeted proteomic analysis of CSF samples of three SMA type 1 patients revealed the lysosomal protease cathepsin D as a candidate biomarker. Subsequent validation analysis in a larger cohort of 31 pediatric SMA patients (type 1, n = 12; type 2, n = 9; type 3, n = 6; presymptomatically treated, n = 4; age = 0–16 years) revealed a significant decline of cathepsin D levels in SMA patients aged ≥2 months at the start of treatment. Although evident in all older age categories, this decline was only significant in the group of patients who showed a positive motor response. Moreover, downregulation of cathepsin D was evident in muscle biopsies of SMA patients. Conclusions We identified a decline of cathepsin D levels in CSF samples of SMA patients under nusinersen treatment that was more pronounced in the group of "treatment responders" than in "nonresponders." We believe that our results indicate a suitability of cathepsin D levels as a possible biomarker in SMA also in older patients, in combination with analysis of peripheral neurofilament light chain in adolescents or alone in adult patients.

Febrile ulceronecrotic Mucha-Habermann disease (FUMHD) is a rare inflammatory dermatological disease. A case of a 13-year-old boy with FUMHD possibly triggered by mycoplasma infection is presented. Based on FUMHD cases identified in a MEDLINE literature search, demographic, treatment, and outcome data were analyzed. An FUMHD mortality risk score is proposed based on the likelihood ratios of risk factors for a fatal outcome. Our FUMHD case had marked leukopenia and thrombocytopenia at admission. He recovered without systemic immunosuppressive treatment. Literature review revealed 119 FUMHD cases. Overall lethality was 14/119 (12%, CI 6-17%), and lethality in children was lower (1/54, 2%, CI 0-6%) compared to adults (13/65, 20%, CI 11-31%). Risk factors for a fatal outcome (likelihood ratio; P) were sepsis (24.97, P < 0.001), adult vs. pediatric patient age (11.19; P = 0.001), systemic involvement (19.97, P < 0.001), and mucosal involvement (4.58; P = 0.032). The proposed FUMHD mortality risk score = Age/ 10 + 4 + 4 (if systemic involvement) + 1 (if mucosal involvement) was discriminative (sensitivity 93%, specificity 77%). In FUMHD, immune-suppressive treatment intensity should be balanced against the mortality risk, as infectious complications are a frequent cause of death.