Huntington's disease: pathogenic mechanisms and therapeutic targets

Huntington's disease (HD) is a tandem repeat disorder involving neurodegeneration and a complex combination of symptoms. These include psychiatric symptoms, cognitive deficits culminating in dementia, and the movement disorder epitomised by motor signs such as chorea. HD is caused by a CAG repeat expansion encoding an extended tract of the amino acid glutamine in the huntingtin protein. This polyglutamine expansion appears to induce a 'change of function', possibly a 'gain of function', in the huntingtin protein, which leads to various molecular and cellular cascades of pathogenesis. In the current review, we will briefly describe these broader aspects of HD pathogenesis, but will then focus on specific aspects where there are substantial bodies of experimental evidence, including oxidative stress, mitochondrial dysfunction, glutamatergic dysfunction and neuroinflammation. Furthermore, we will review recent preclinical therapeutic approaches targeting some of these pathogenic pathways, their clinical implications and future directions.