The rate of increase was significantly greater in HTT mutation carriers with premanifest Huntington's disease than in controls (0·043 log pg/mL per year [0·018], p=0·0161) but did not differ significantly between those with premanifest and manifest Huntington's disease (0·034 log pg/mL per year [0·018], p=0·0547) or between those with manifest Huntington's disease and controls (0·009 log pg/mL per year [0·018], p=0·630). The gene discussed is HTT; the disease is Huntington disease.