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. 2023 Sep 8;10(5):937–954. doi: 10.3233/JND-230054

Table 1.

Candidate biomarkers for SMA

Biomarker Notes References
Biomolecular candidates
SMN protein Lower levels of circulating SMN protein correlate with more severe/ advanced disease. [18, 39, 48, 57, 81, 104106]
Neurofilament Higher levels of NF indicate greater axonal degradation and more severe/advanced disease. [78, 107118, 167]
Muscle indicators Creatinine, creatine kinase, and other markers of muscle damage are elevated in more advanced SMA. [122124]
Genetic candidates
SMN2 gene copy number or polymorphisms Fewer copies of SMN2 gene correlate with less SMN protein and more severe/advanced disease. [10, 1316, 8183]
Modifier genes The expression of some non-SMN genes may modify the SMA phenotype. [73, 8489]
Gene transcription and
splicing regulators
Micro RNAs Preclinical and clinical research suggests different miRNAs may be expressed differentially according to SMA severity. [9094]
Methylation factors Methylation of SMN2 impacts its expression and may be a way to measure SMN protein production. Genome-wide methylation patterns and methylation of genes other than SMN1 and SMN2 may correlate with disease severity. [9599]
Long non-coding RNAs Non-coding RNAs might impact gene expression, including activation of SMN2. [100103]
Imaging candidates
Muscle imaging approaches MRI may be useful in determining the degree of SMA severity, muscle atrophy, and response to treatment. [128133]
Electrical impedance myography (EIM) EIM measures action potentials on the surface of muscles following stimulation and has been shown to be sensitive to nuanced advancement of disease progression. [75, 125127]
Electrophysiological parameters
Compound muscle action potential (CMAP) CMAP measurements indicate the degree to which a muscle responds to motor nerve stimulation. CMAP responses decline with disease onset. [45, 75, 134138, 175]
Motor unit number estimation (MUNE) MUNEs are obtained through several methods, such as applying increasing levels of stimulus to estimate the number of motor units that remain. [134, 135, 138, 175179]
Repetitive nerve stimulation (RNS) RNS measures of function of the neuromuscular junction and is an exploratory indicator of SMA disease state. [180182]