Calpainopathies (LGMD2A)
Compared with LGMD2I, in patients with LGMD2A, caused by mutation in the calpain-3 gene, we observed a very similar and consistent clinical and muscle imaging phenotype. As in LGMD2I, muscle MRI images have confirmed the clinical observation that in LGMD2A there is early and predominant involvement of posterior compartment muscles such as the gluteus maximus in the pelvis, semimembranosus, biceps femoris and adductor muscles in the thigh, with relative sparing of the vastus lateralis, sartorius and gracilis. These findings were also later confirmed by others [41]. Contrary to LGMD2I, there are, however, some important differences: the vastus lateralis is spared more in LGMD2A compared with LGMD2I; the medial gastrocnemius and soleus muscles are much more selectively involved compared with the diffuse affliction seen in LGMD2I, and hypertrophy of the tibialis anterior muscle is only rarely present in LGMD2A.