Pathophysiology and molecular basis of selected metabolic abnormalities in Huntington's disease

Huntington's disease (HD) is an incurable, devastating neurodegenerative disease with a known genetic background and autosomally dominant inheritance pattern. HTT gene mutation (mHTT) is associated with polymorphic fragment elongation above 35 repeats of the CAG triplet. The mHTT product is an altered protein with a poly-Q elongated fragment, with the highest expression determined in the central nervous system (CNS) and with differentiated expression outside the CNS. A drastic loss of striatal and deeper layers of the cerebral cortex neurons was determined in the CNS, but muscle and body weight mass loss with dysfunction of many organs was also observed. HD symptoms include neurological disturbances, such as choreal movements with dystonia, speech and swallowing impairments, and additionally a variety of psychiatric and behavioral symptoms with cognitive decline have been described. They are the result of disturbances of several cellular pathways related to signal transmission, mitochondrial dysfunction and energy metabolism impairment shown by gene and protein expression and alteration of their functions. Impairment of energy processes demonstrated by a decrease of ATP production and increase of oxidative stress markers was determined in- and outside of the CNS in glycolysis, the Krebs cycle and the electron transport chain. A correlation between the increase of energy metabolism impairment level and the increase in number of CAG repeats in HTT has often been described. The energy metabolism study is an initial stage of sensitive biomarkers and a new therapeutic investigative option for early application in order to inhibit pathological processes in HD. Identification of pathological changes outside the CNS requires a reevaluation of diagnostic and therapeutic rules in HD.