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The availability of disease modifying therapies for spinal muscular atrophy (SMA) have created an urgent need to identify clinically meaningful biomarkers that provide insight into disease progression and therapeutic response. microRNAs (miRNA) have been shown to be involved in the pathogenesis of SMA and have the potential to provide insight within the field of SMA. miRNA-sequencing was utilized to identify differential miRNA expression in the cerebrospinal fluid (CSF) in six children with SMA treated with nusinersen in this exploratory study. Fourteen differentially expressed miRNAs were significantly altered in CSF from baseline to follow-up during treatment with nusinersen. The greatest magnitude of change was noted in miR-7-5p, miR-15a-5p, miR-15b-3p/5p, miR-126-5p, miR-128-2-5p and miR-130a-3p which encompassed a spectrum of functions predominantly in neurogenesis, neuronal differentiation and growth. The dominant signaling pathways identified in this study were the mammalian target of rapamycin and the mitogen-activated protein kinase signaling pathways. This study identified multiple miRNAs that were involved in the complex interplay between neurodevelopment and neurodegeneration. [ABSTRACT FROM AUTHOR]

Aim: This study dynamically designed, evaluated, and implemented the components of an Australian newborn bloodspot screening (NBS) pilot programme for spinal muscular atrophy (SMA). Method: We used an implementation‐effectiveness study design and continuous interdisciplinary review to measure SMA NBS test protocol performance, identify and overcome laboratory and clinical barriers to implementation, and describe progress during the 2‐year pilot study. Results: The NBS programme screened 252 081 newborn infants from 1st August 2018 to 31st January 2021. Using an NBS pilot test protocol, 21 infants were diagnostically confirmed with SMA. The NBS pilot test protocol had a sensitivity of 100%, specificity greater than 99.9%, false‐positive rate less than 0.001%, a false‐negative rate of 0%, and positive predictive value of 95.5%. A severe phenotype was predicted on the basis of two copies of SMN2 in 57.2% of newborn infants screening positive for SMA. Clinical signs consistent with SMA were evident in 6 out of 21 screen‐positive newborn infants within the first 4 weeks of life. A multidisciplinary team establishing strong partnerships across clinical and laboratory staff was key to implementation. Interpretation: This pilot programme suggests that NBS is essential for early identification of newborn infants at risk of SMA and can be effectively translated into clinical practice. This original article is commented by Mueller‐Felber on page 535 of this issue. [ABSTRACT FROM AUTHOR]

Spinal muscular atrophy (SMA) is associated with developmental disruption of motor axons in ventral roots of the spinal cord alongside motor axon degeneration. The pathogenesis of peripheral axonal change during development is pertinent to understand treatment response. Nerve excitability techniques, stimulating the median motor nerve at the wrist, were utilised to investigate axonal change during neurodevelopment in 24 children with SMA, compared with 71 age‐matched controls. Longitudinal axonal response to nusinersen treatment in 18 children was also investigated. Significant differences in axonal development were noted in the youngest children with SMA, signified by reduced compound muscle action potential (CMAP) (P = 0.030), higher axonal threshold (P = 0.016), rheobase (minimal current amplitude of infinite duration, required to generate an action potential) (P = 0.012) and greater changes in depolarising and hyperpolarising threshold electrotonus. Subexcitability increased in all children with SMA, compared to controls. With treatment, nerve excitability changes were observed prominently in young children, with increases in CMAP, reduction in axonal threshold, fanning‐in of threshold electrotonus, increase in resting current–threshold slope and reduction in subexcitability. Whilst motor axons continue to mature in SMA, developmental delays in passive and active membrane properties occur especially in early childhood. Concurrently, motor axons actively undergo degeneration. Nusinersen restores the developmental trajectory of motor axons reducing degeneration, especially in children with early treatment initiation. Our findings move the field forward in understanding the developmental aspect of childhood‐onset motor neurone diseases and changes in axonal function associated with disease modification. Key points: Pathomechanisms in spinal muscular atrophy involve concurrent neurodevelopmental and neurodegenerative processes.The greatest delays in maturation of the passive and active properties of the peripheral motor axon are seen in early childhood.Nusinersen facilitates developmental recovery of the motor axon whilst also reducing neurodegeneration.Axonal dysfunction is reversed with SMN repletion particularly when intervention occurs early in development. [ABSTRACT FROM AUTHOR]