MR relaxometry in Huntington's disease: Correlation between imaging, genetic and clinical parameters

Huntington's disease (HD) is an autosomal dominant inherited neurodegenerative disease. It has been hypothesized that changes of iron content in the brain may be involved in the pathogenesis of HD. To ascertain the hypothesis, we investigated the relationship between T2 relaxation time (T2), the number of cytosine–adenine–guanine triplet repeats (CAG) and clinical status in patients suffering from HD. 34 HD patients (mean age 50.1 ± 11.8 standard deviation (SD) years) and 34 control subjects (49.6 ± 13.3) were scanned using a 1.5 tesla magnetic resonance (MR) scanner and the patients underwent clinical and genetic testing. A multiple echo sequence was employed for T2 measurements. T2 from healthy volunteers matched previous studies. A T2 shortening was found in the pallidum of HD patients compared to controls (65.4 ± 6.4 ms vs. 71.8 ± 3.6 ms, P < 0.00001). A correlation between the number of CAG and T2 was found for the left pallidum (decrease in T2, P < 0.05) and an inverse correlation for the left caudate (increase in T2, P < 0.05). In HD patients, alterations in iron levels may be caused by an alteration in its axonal transport. The observed T2/CAG covariations may reflect changes in levels and forms of iron: this suggests that HD patients with a higher genetic load have more ferritin-bound (“safe form”) iron in the pallidum and/or more low-molecular (“toxic”) iron in the caudate. An increase in “toxic” iron in the caudate may enable oxidative stress and thus underlie progression of the disease.