Reassessment of motor-behavioural test analyses enables the detection of early disease-onset in a transgenic mouse model of amyotrophic lateral sclerosis

As a model for amyotrophic lateral sclerosis (ALS), transgenic hSOD1G93A mice constitute the standard tool for evaluating future therapeutic strategies. Due to axonal retraction from neuromuscular junctions, the animals suffer from muscle wasting leading to weakness and paralysis of the extremities, which in early stages can be detected by measuring weight loss. Suspecting that underlying mechanisms might yield subtle neuromuscular abnormalities ahead of weight loss onset, we wanted to determine a behavioural test to detect disease onset time earlier. We compared the monitoring of weight with the "forced" examination of grip strength and the investigation of freely behaving animals within an open field. Additionally, we compared two different data analysis methods: (1) two-way ANOVA with Bonferroni correction (2) break point analysis calculating symptom onset time points for each animal. Break point analysis revealed onset times that significantly preceded those obtained by standard two-way ANOVA. Open field analysis of freely moving animals could not give an advantage over weight loss measurements. Grip strength assessment of hindlimbs detected disease onset 36 days before the first evidence of weight loss, providing a maximal treatment window of 84 days on average before the death of male animals. We conclude that grip strength analysis of hindlimbs is a very sensitive and reproducible motor behavioural test, which can even be applied to small cohorts of animals. Combined with break point analysis, it represents the method of choice to detect early disease onset in hSOD1G93A mice.