Spinal Muscular Atrophy Biomarker Measurements from Blood Samples in a Clinical Trial of Valproic Acid in Ambulatory Adults

BACKGROUND Clinical trials of therapies for spinal muscular atrophy (SMA) that are designed to increase the expression the SMN protein ideally include careful assessment of relevant SMN biomarkers. OBJECTIVE In the SMA VALIANT trial, a recent double-blind placebo-controlled crossover study of valproic acid (VPA) in ambulatory adult subjects with SMA, we investigated relevant pharmacodynamic biomarkers in blood samples from SMA subjects by direct longitudinal measurement of histone acetylation and SMN mRNA and protein levels in the presence and absence of VPA treatment. METHODS Thirty-three subjects were randomized to either VPA or placebo for the first 6 months followed by crossover to the opposite arm for an additional 6 months. Outcome measures were compared between the two treatments (VPA and placebo) using a standard crossover analysis. RESULTS A significant increase in histone H4 acetylation was observed with VPA treatment (p = 0.005). There was insufficient evidence to suggest a treatment effect with either full length or truncated SMN mRNA transcript levels or SMN protein levels. CONCLUSIONS These measures were consistent with the observed lack of change in the primary clinical outcome measure in the VALIANT trial. These results also highlight the added benefit of molecular and pharmacodynamic biomarker measurements in the interpretation of clinical trial outcomes.