Advanced oxidation protein products in serum of patients with myotonic disease type I: association with serum gamma-glutamyltransferase and disease severity.

Steinert's disease (myotonic dystrophy type 1; MD) is caused by a CTG trinucleotide expansion on 19q13.3. Although the pathogenic mechanism underlying multisystem involvement in MD is still unclear, a role of oxidative stress in this disease has been suggested. We investigated 39 MD patients to assess the plasma concentration of advanced oxidation protein products (AOPPs) and gamma-glutamyltransferase (GGT) and related them to clinical severity scores. Plasma AOPP levels (p=0.021), total serum GGT activity (p=0.0005) and GGT activity associated with low-density lipoprotein (p=0.0021) were significantly higher in patients than in controls. There was significant correlation between serum GGT levels and AOPPs (r=0.5831; p=0.0022). A statistically significant increase in serum GGT with age was found in MD patients (p=0.0193). Receiver operating characteristic curve analysis showed that higher AOPP levels were significantly associated with extra-muscular signs of the disease, i.e., cataracts and heart involvement (area under the curve+/-SE=0.908+/-0.083), but not with muscular involvement. The concomitant increment in GGT and AOPPs indicates a possible role of oxidative stress in the pathogenesis of MD type 1, while the association of increased AOPP levels with extra-muscular signs of the disease suggests that individual susceptibility to oxidative stress can modulate the extra-muscular phenotype of the disease.