FKRP-related myopathies (LGMD2I)
A few years ago, a novel gene encoding a putative glycosyltransferase, fukutin-related protein (FKRP), was found to be responsible for both a novel form of congenital muscular dystrophy (MDC1C) and for a form of limb girdle muscular dystrophy (LGMD2I) [38, 39]. Recently, we performed a systematic clinical and muscular MRI assessment in several LGMD2I patients and compared these findings with those of other patients with genetically confirmed diagnosis of other forms of autosomal recessive LGMDs or dystrophinopathies [40].
All LGMD2I patients had a characteristic muscular phenotype on MRI of the lower extremities that demonstrated marked signal changes in the adductor muscles, the posterior thigh and posterior calf muscles. Furthermore, data of patients with different clinical disease severity pointed towards a specific temporal pattern. At the pelvic level, the gluteus maximus was involved earlier and more severely than the gluteus medius. At the thigh level the earliest and most severe changes were observed in the adductor (magnus) muscles and the biceps femoris. With further progression degenerative changes were noticed in the remaining hamstring muscles and to a lesser degree in the vastus lateralis and vastus intermedius muscles. Involvement of the vastus medialis and rectus femoris was only observed in the patient with advanced disease, while the sartorius and gracilis muscles were relatively spared. In the lower legs relatively diffuse changes in the medial head of the gastrocnemius and the soleus muscle were observed early in the disease, while involvement of the anterior compartment muscles was only observed in later stages of the disease. The tibialis anterior muscle was usually spared and often hypertrophied.