Friedreich's ataxia 1979: an overview.

This overview summarizes the investigations carried out during the second part of Phase Two of the Quebec Cooperative Study of Friedreich's Ataxia. These investigations outline in more details the fundamental role played by an abnormality in the fatty acid composition (deficient linoleic acid, 18:2) of the cholesterol esters of high density lipoproteins (HDL) in the phenotypic expression of the disease. They postulate a defective incorporation of linoleic acid to surface phosphatidylcholine of chylomicrons and consequent relative and absolute decreases in lipoprotein protein components because of overpacking with defective cholesteryl esters. Secondarily to these changes, the postulated lack of activation of the lipoamide dehydrogenase (LAD) of the pyruvate dehydrogenase (PDH) complex could result in slow pyruvate oxidation, glucose intolerance, deficient synthesis of acetylcholine, and depletion of glutamic and aspartic acid pools. In parallel, abnormal phosphatidyl-choline molecules could be incorporated to membranes, resulting in specific defects in some functions of these membranes, including transport of calcium and/or taurine and myelinization. The framework of an understanding of Friedreich's ataxia is now available, but much fundamental and clinical work remains to be done to fill in and prove each one of these postulated steps.