Electrophysiological biomarkers in spinal muscular atrophy: proof of concept

Abstract

ObjectivePreclinical therapies that restore survival motor neuron (SMN) protein levels can dramatically extend survival in spinal muscular atrophy (SMA) mouse models. Biomarkers are needed to effectively translate these promising therapies to clinical trials. Our objective was to investigate electrophysiological biomarkers of compound muscle action potential (CMAP), motor unit number estimation (MUNE) and electromyography (EMG) using an SMA mouse model.MethodsSciatic CMAP, MUNE, and EMG were obtained in SMNΔ7 mice at ages 3–13 days and at 21 days in mice with SMN selectively reduced in motor neurons (ChATCre). To investigate these measures as biomarkers of treatment response, measurements were obtained in SMNΔ7 mice treated with antisense oligonucleotide (ASO) or gene therapy.ResultsCMAP was significantly reduced in SMNΔ7 mice at days 6–13 (P < 0.01), and MUNE was reduced at days 7–13 (P < 0.01). Fibrillations were present on EMG in SMNΔ7 mice but not controls (P = 0.02). Similar findings were seen at 21 days in ChATCre mice. MUNE in ASO-treated SMNΔ7 mice were similar to controls at day 12 and 30. CMAP reduction persisted in ASO-treated SMNΔ7 mice at day 12 but was corrected at day 30. Similarly, CMAP and MUNE responses were corrected with gene therapy to restore SMN.InterpretationThese studies confirm features of preserved neuromuscular function in the early postnatal period and subsequent motor unit loss in SMNΔ7 mice. SMN restoring therapies result in preserved MUNE and gradual repair of CMAP responses. This provides preclinical evidence for the utilization of CMAP and MUNE as biomarkers in future SMA clinical trials.

The neuromuscular impact of symptomatic SMN restoration in a mouse model of spinal muscular atrophy

“…Similar to what we previously have shown with early therapy on day of birth, CMAP in early-treated SMA mice (P2-ASO) was not statistically different compared with sham-treated SMA or late-treated SMA (P4-ASO and P6-ASO)(Arnold et al, 2014). MUNE was preserved in early-treated SMA (P2-ASO) and identified differences between early-(P2-ASO) and late-treated (P6-ASO) animals.…”

The neuromuscular impact of symptomatic SMN restoration in a mouse model of spinal muscular atrophy

“…Similar to what we previously have shown with early therapy on day of birth, CMAP in early-treated SMA mice (P2-ASO) was not statistically different compared with sham-treated SMA or late-treated SMA (P4-ASO and P6-ASO)(Arnold et al, 2014). MUNE was preserved in early-treated SMA (P2-ASO) and identified differences between early-(P2-ASO) and late-treated (P6-ASO) animals.…”

Normalization of Patient-Identified Plasma Biomarkers in SMNΔ7 Mice following Postnatal SMN Restoration

“…Blood samples were obtained from some of the animals from this previously published study for analysis of plasma analytes. Consistent with our prior study, CMAP, MUNE, and SMUP comparison between ASO-SMA and ASO-Het showed statistically significant difference between groups for CMAP at the P12 measurement, but no other parameter showed a significant change between groups (Fig 5) [52]. Plasma protein analytes were correlated with electrophysiological measures at P30 and P90.…”

Hyperexcitability precedes motoneuron loss in the Smn2B/− mouse model of spinal muscular atrophy

“…CMAP and MUNE measurements were obtained in 2B/Ϫ and sibling littermate control mice at P8 -P16 (Tables 1 and 2) to gain insight into the natural history of motor unit function in this SMA model and for comparison with findings in the ⌬7 SMA model. Consistent with humans during early development and murine data reported in the ⌬7 SMA mouse, CMAP amplitudes in control and 2B/Ϫ mice increased over time (Arnold et al 2014;Parano et al 1993) (P Ͻ 0.0001; Table 1 and Fig. 2A).…”

The neuromuscular impact of symptomatic SMN restoration in a mouse model of spinal muscular atrophy

“…Similar to what we previously have shown with early therapy on day of birth, CMAP in early-treated SMA mice (P2-ASO) was not statistically different compared with sham-treated SMA or late-treated SMA (P4-ASO and P6-ASO)(Arnold et al, 2014). MUNE was preserved in early-treated SMA (P2-ASO) and identified differences between early-(P2-ASO) and late-treated (P6-ASO) animals.…”

Normalization of Patient-Identified Plasma Biomarkers in SMNΔ7 Mice following Postnatal SMN Restoration

“…Blood samples were obtained from some of the animals from this previously published study for analysis of plasma analytes. Consistent with our prior study, CMAP, MUNE, and SMUP comparison between ASO-SMA and ASO-Het showed statistically significant difference between groups for CMAP at the P12 measurement, but no other parameter showed a significant change between groups (Fig 5) [52]. Plasma protein analytes were correlated with electrophysiological measures at P30 and P90.…”

Hyperexcitability precedes motoneuron loss in the Smn2B/− mouse model of spinal muscular atrophy

“…CMAP and MUNE measurements were obtained in 2B/Ϫ and sibling littermate control mice at P8 -P16 (Tables 1 and 2) to gain insight into the natural history of motor unit function in this SMA model and for comparison with findings in the ⌬7 SMA model. Consistent with humans during early development and murine data reported in the ⌬7 SMA mouse, CMAP amplitudes in control and 2B/Ϫ mice increased over time (Arnold et al 2014;Parano et al 1993) (P Ͻ 0.0001; Table 1 and Fig. 2A).…”

The neuromuscular impact of symptomatic SMN restoration in a mouse model of spinal muscular atrophy

“…Similar to what we previously have shown with early therapy on day of birth, CMAP in early-treated SMA mice (P2-ASO) was not statistically different compared with sham-treated SMA or late-treated SMA (P4-ASO and P6-ASO)(Arnold et al, 2014). MUNE was preserved in early-treated SMA (P2-ASO) and identified differences between early-(P2-ASO) and late-treated (P6-ASO) animals.…”

Normalization of Patient-Identified Plasma Biomarkers in SMNΔ7 Mice following Postnatal SMN Restoration

“…Blood samples were obtained from some of the animals from this previously published study for analysis of plasma analytes. Consistent with our prior study, CMAP, MUNE, and SMUP comparison between ASO-SMA and ASO-Het showed statistically significant difference between groups for CMAP at the P12 measurement, but no other parameter showed a significant change between groups (Fig 5) [52]. Plasma protein analytes were correlated with electrophysiological measures at P30 and P90.…”

Hyperexcitability precedes motoneuron loss in the Smn2B/− mouse model of spinal muscular atrophy

“…CMAP and MUNE measurements were obtained in 2B/Ϫ and sibling littermate control mice at P8 -P16 (Tables 1 and 2) to gain insight into the natural history of motor unit function in this SMA model and for comparison with findings in the ⌬7 SMA model. Consistent with humans during early development and murine data reported in the ⌬7 SMA mouse, CMAP amplitudes in control and 2B/Ϫ mice increased over time (Arnold et al 2014;Parano et al 1993) (P Ͻ 0.0001; Table 1 and Fig. 2A).…”