[3] Bethlem myopathy 2 (BTHLM2), formerly known as myopathic-type Ehlers–Danlos syndrome, is caused by a mutation on the COL12A1 gene coding for type XII collagen.

[3] In 2017, an international workshop proposed a redefined criteria and naming system for limb-girdle muscular dystrophies.

[11] Early on, there may be distal laxity (hypermobility), but all of those with Bethlem myopathy eventually develop multiple joint contractures: long finger flexors, wrists, elbows, hips, knees and ankles.

This unusual pattern is described as a "central cloud" and is also a distinguishing feature, as it is not seen in the rectus femoris of LMNA-related Emery-Dreifuss myopathy.

[12] Bethlem myopathy 1 may also include neonatal-onset torticollis (neck contracture) and hypotonia ("floppy baby"), delayed motor mile stones, with respiratory difficulties potentially occurring later in life.

[20][12] Contractures presenting in infancy may resolve by age 2 years, but reoccur as the disease progresses, typically by late of the first decade or early teens.

[14][11] In another family, only the more severely affected older patient showed significant abnormality, by having symmetrical fatty atrophy of the femoral quadriceps of the thigh, the adductor and medial gastrocnemius muscles of the calf; as well as asymmetrical fatty atrophy of the adductor longus of the thigh.

[11] Bethlem myopathy 2 also differs by including the possibility of scapula winging, pectus excavatum, stooped posture, kyphosis (hunchback), micrognathia, retrognathia, and a high-arched palate.

[11] The disease may be diagnosed based on a clinical examination, which identifies signs and symptoms generally associated with the people who have the condition.

[21] Ullrich congenital muscular dystrophy (UCMD) involves mutations on the same genes as Bethlem myopathy, but has a more severe presentation, with the ability to walk (ambulation) typically being lost between the ages of 5–15 years.

[12] Autosomal recessive myosclerosis myopathy is allelic to the COL6A2 gene, it includes multiple contractures of the joints with slender muscles which are infiltrated by connective tissue and fibrosis, giving them a firm, "woody" feel upon palpitation.

It is believed that physical therapy, stretching exercises, orthoses such as braces and splints, and mobility aids like a walker or wheelchair are beneficial to patient's condition.

[7] Surgical options could be considered in rare instances, in order to help with joint contractures or scoliosis.