Abstract
Myopathic Ehlers-Danlos syndrome (RmEDS) is an emerging hybrid phenotype that combines connective and muscle tissue abnormalities. It has been associated with variants of the COL12A1 gene, which are known as Ullrich congenital muscular dystrophy-2 (UCMD2; 616470) and Bethlem myopathy-2 (BTHLM2; 616471). Here, we report two splicing mutations of COL12A1 identified in three patients from two unrelated families who present a combination of joint hypermobility and axial, distal, and proximal weakness. The muscular strength of their neck and limb muscles was assessed at 4/5 (MRC); however, when measured with a myometer, the expected percentage by age and sex ranged from 35% to 40% for elbow flexion, 37% to 75% for knee extension, and was 50% for neck flexion. In addition to confirming the characteristic atrophy of the rectus femoris, we presented evidence of involvement of the neck and lumbar muscles through MRI and CT imaging. In vitro studies revealed filamentous disorganization and an altered pattern of collagen XII alpha 1 chain migration due to the skipping of exons 55 and 56 of collagen XII. Additionally, we review the myopathic involvement of COL12-RM in 30 patients across 18 families with dominant mutations and 15 patients from 13 families with recessive mutations.