A usually autosomal dominant inherited movement disorder caused by mutations in the COL6A1, COL6A2, and COL6A3 genes. It is characterized by progressive muscle weakness and joint stiffness in the fingers, wrists, elbows, and ankles. The disease is Monarch Disease Ontology id MONDO_0008029 (Bethlem myopathy). Also known as: Bethlem myopathy type 1, benign autosomal dominant myopathy, benign congenital muscular dystrophy.