G13 Abnormal responses to visual cortex activation in early stage Huntington disease patients using 31P-NMR spectroscopy

Abstract

Objective To test the hypothesis that brain energy metabolism is abnormal in patients at an early stage of Huntington disease (HD). Background Energy metabolism has been a major focus of HD research for many years due to several observations in both patients and models of the disease. However, there are currently no in vivo biomarkers of brain energy metabolism in HD. Methods We coupled noninvasive 31P-NMR spectroscopy with activation of the occipital cortex in order to measure the levels of ATP, phosphocreatine (PCr) and inorganic phosphate (Pi) before, during and after a visual stimulus. We studied 15 HD patients at an early stage of the disease (mean motor UHDRS =18±9) and 15 age- and sex-matched controls. Results In controls, we observed an 11% increase in Pi/PCr ratio (p=0.024) and a 13% increase in Pi/ATP ratio (p=0.016) during brain activation, reflecting increased ATP synthesis and ADP levels. Subsequently, controls had a return to baseline levels during recovery (p=0.012 et 0.022 respectively). In HD patients, both Pi/PCr and Pi/ATP ratios were unchanged during and after visual stimulation, reflecting altered mitochondrial bioenergetics. In addition, in HD patients the ratio of Pi/ATP correlated with the UHDRS score during the activation (p=0.014) and recovery periods (p=0.009), while Pi/PCr ratio correlated with the UHDRS score during recovery (p=0.016), reflecting a correlation between brain energy metabolism and disease severity in HD. Conclusions 31Phosphorus nuclear magnetic resonance spectroscopy could provide functional biomarkers of brain energy deficit to monitor therapeutic efficacy in Huntington disease.