G.P.277: LGMD2I: Is there a relationship between clinical phenotype, morphological alterations and level of alpha-dystroglycan glycosylation in patients with the same FKRP genotype?

Abstract

To investigate if there is a correlation between clinical expression (duration of disease, age, walking function) and morphological alterations in affected muscle (structural changes, immunohistochemical and the level of alpha-DG glycosylation) among 25 patients with Limb Girdle Muscular Dystrophy type 2I (LGMD2I) all with the common C.826C>A mutation ). Muscle biopsies were obtained from 25 patients. Quantitative evaluation of morphological alterations in muscle sections, and immunohistochemistry (IHC) with antibodies directed against the alpha-dystroglycan glycan epitope, was performed by light microscopy. A semi-quantitative assessment of changes was recorded, point-graded and summarized as morphological sum-score for each biopsy.. Western blot (WB) analysis on muscle biopsy homogenates were carried with antibodies directed towards the core alpha-DG as well as the alpha-DG-glycan epitope. Laminin overlay was included. Muscle biopsies from 25 patients with LGMD2I presented large variation in morphological features. All biopsies presented reduced molecular weight of alpha-DG as detected with alpha-DG core antibody on WB analysis. Immunohistochemistry and WB analysis directed towards the alpha-DG-glycan epitope, as well as laminin overlay, demonstrated large variation in signal intensity among the LGMD2I patients. Results from IHC and WB/laminin overlay correlated poorly. There was no obvious correlation between ages at onset or duration of disease at biopsy versus the level of alpha-DG glycosylation. Likewise, there was no apparent association between severities of disease and the sum-scores of structural changes in the muscle biopsies. The clinical and morphological variability seen among LGMD2I patients with identical FKRP genotype must therefore be explained by other genetic or environmental mechanisms.