Mitochondrial hydroxyapatite deposits in spinocerebellar degeneration.

We report the presence of crystalline deposits of calcium hydroxyapatite in the mitochondria of 2 children with sporadic spinocerebellar degeneration. The deposits, identified by electron microscopy, were found in the mitochondria of neurons and smooth muscle cells in one patient and in only smooth muscle cells in the second child, but not in other cell types. The calcific nature of the deposits was confirmed by laser microprobe mass analysis. The calcium overload may interfere with mitochondrial function, as has been shown in the cardiomyopathic strain of the Syrian hamster, a model of the cardiomyopathy of Friedreich's ataxia.