This is breakthrough research. Occam's razor tell us that this is the basic (primary) HD defect. This is not good news for the long term success of tissue implants.--Jerry 03/01/98
Ann Neurol. 1998 Mar; 43(3): 397-400. Arenas J, et al.

We found a variable defect of complex I of the mitochondrial respiratory chain, ranging in severity from 25% to 63% of control values, in muscle of patients with Huntington's disease (HD).

The most severe defect was observed in the patient with the greatest expansion of CAG triplets. Muscle morphology showed myopathic changes such as moth-eaten fibers, angulated fibers, increased subsarcolemmal oxidative activities, or an increased number of enlarged mitochondria with abnormal cristae.

Multiple mitochondrial DNA deletions were found by polymerase chain reaction (PCR) analysis in muscle of the patient with the most severe defect of complex I. Our data further support the involvement of energetic defects and oxidative damage in muscle of patients with HD.

Mitochondria are the structures within our cells that produce energy. The food we eat is oxidized and converted to energy stored in phosphate bonds in the adenosine triphosphate (ATP) molecule. Energy is released when ATP converts to adenosine diphosphate (ADP). Five respiratory complexes preform the various conversions. Arenas, et al, have identified HD as a defect of the first complex. Intense exercise causes similiar muscle damage.]
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J Biol Chem 1998 May 22;273(21):12753-12757. Davey GP, et al.

Decreases in mitochondrial respiratory chain complex activities have been implicated in neurodegenerative disorders such as Parkinson's disease, Huntington's disease and Alzheimer's disease However the extent to which these decreases cause a disturbance in oxidative phosphorylation and energy homeostasis in the brain is not known.

We therefore examined the relative contribution of individual mitochondrial respiratory chain complexes to the control of linked substrate oxidative phosphorylation in synaptic mitochondria. Titration of complex I, III, and IV activities with specific inhibitors generated threshold curves that showed the extent to which a complex activity could be inhibited before causing impairment of mitochondrial energy metabolism .

Complex I, III, and IV activities were decreased by approximately 25, 80, and 70%, respectively, before major changes in rates of oxygen consumption and ATP synthesis were observed.

These results suggest that, in mitochondria of synaptic origin, complex I activity has a major control of oxidative phosphorylation, such that when a threshold of 25% inhibition is exceeded, energy metabolism is severely impaired, resulting in a reduced synthesis of ATP.

Additionally, depletion of glutathione , which has been reported to be a primary event in idiopathic Parkinson's disease, eliminated the complex I threshold in PC12 cells, suggesting that antioxidant status is important in maintaining energy thresholds in mitochondria. The implications of these findings are discussed with respect to neurodegenerative disorders and energy metabolism in the synapse.