R. Lodi, B. Rajagopalan, A. Schapira
Oct 1, 2003
Annals of Neurology
We read with interest the article by Bunse and colleagues confirming our previous work that demonstrated an impairment of cardiac bioenergetics in 18 patients with Friedreich’s ataxia, a nuclear encoded mitochondrial disorder due to a GAA trinucleotide repeat expansion in the frataxin gene. The authors reported a negative correlation between septal wall thickness (IVS) and both cardiac phosphocreatine to adenosine triphosphate (PCr/ATP) and inorganic phosphate to PCr ratios (Pi/PCr). Surprisingly, these correlations were obtained including both Friedreich’s ataxia patients and healthy subjects. However, inspection of the distribution of healthy volunteers’ echocardiographic and phosphorus MR spectroscopy (P-MRS) measurements reported in Figure 2, shows no correlation between IVS and Pi/PCr or PCr/ATP. Nevertheless, the inclusion of healthy subjects with low IVS may have contributed to the significance of the reported correlations. It would be more relevant to know if, in the patient group, there was a correlation between echocardiographic and P-MRS variables and their relationship with the expansion of the GAA repeat. In our previous study, we did not find any correlation between cardiac PCr/ATP and echocardiographic variables nor GAA repeats numbers in Friedreich’s ataxia patients. Unfortunately, because of the different P-MRS acquisition protocol we could not asses the cardiac content of inorganic phosphate. In the study by Bunse and colleagues, cardiac Pi/ATP was elegantly measured, and a clear demonstration in Friedreich’s ataxia patients of a relationship between cardiac bioenergetics and echocardiographic variables and/or underlying genetic abnormality would add important clues for the understanding of the development of cardiomyopathy in this condition.