Marked variation in the cardiomyopathy associated with Friedreich's ataxia

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Abstract
Objective To document the cardiac phenotype associated with Friedreich’s ataxia, a recessively inherited disorder characterised by spinocerebellar degeneration. Setting Individuals with Friedreich’s ataxia who accepted the invitation to participate in the study. Hypothesis The cardiomyopathy associated with Friedreich’s ataxia may offer a human model for the study of factors modulating cardiac hypertrophy. Methods 55 patients (mean (SD) age 30 (9) years) with a clinical diagnosis of Friedreich’s ataxia were studied by clinical examination, electrocardiography, cross sectional and Doppler echocardiography, and analysis of the GAA repeat in the first intron of the frataxin gene. Results A wide variety of cardiac morphology was documented. Subjects with normal frataxin alleles had no evidence of cardiomyopathy. In homozygous subjects, a relation was found between the thickness of the interventricular septum (r = 0.53, p < 0.005), left ventricular mass (r = 0.48, p < 0.01), and the number of GAA repeats on the smaller allele of the frataxin gene. No relation was shown between the presence of electrocardiographic abnormalities (mainly repolarisation changes) and either the pattern of ventricular hypertrophy (if present) and degree of neurological disability or the length of time since diagnosis. No tendency to ventricular thinning or dilatation with age was found. Although ventricular systolic function appeared impaired in some cases, Doppler studies of ventricular filling were within the normal range for age. Conclusions The cardiomyopathy associated with Friedreich’s ataxia shows a variable phenotype which is not concordant with the presence of ECG abnormalities or the neurological features of the condition. As the genetic basis for Friedreich’s ataxia has been established, further studies will help to clarify the molecular mechanisms of the cardiac hypertrophy.