Plasma valine, leucine, and isoleucine levels were significantly lower in the HD group compared with controls (P = .02, <.001, and .002, respectively). In addition, we found a significant decrease of valine, leucine, and isoleucine in moderately affected patients and patients at a severe stage of the disease (Figure). Leucine was also significantly decreased in patients at a very mild stage of the disease and in presymptomatic individuals (Figure). Simple linear regression showed that plasma BCAA were not correlated with the UHDRS. However, we found that valine was negatively correlated with the number of CAG repeats (P = .01, adjusted r2 = 0.086). After adjusting for BMI and sex, we confirmed that there was a negative association between valine and CAG repeats (P = .02, adjusted r2 = 0.309). For every 1-unit increase in CAG, valine decreased by −3.33. We also found a significant association between leucine and CAG repeats (P = .04, adjusted r2 = 0.372), with an association dependent on BMI due to the interaction. For every 1-unit increase in CAG, leucine decreased by −1.50 for the mean value of BMI (23.2).