The affected children usually appear normal at birth and the symptoms become recognizable at 1 to 3 years of age.
Malignant hyperthermia is a potentially lethal hazard during anesthesia.
Micrognathia is usually associated. Narrow palpebral fissures due to medial displacement of the outer canthi. Highly arched palate is common. Hip dysplasia with acetabular flattening and severe coxa vara, congenial hip dislocation, joint contractures, metaphyseal widening of the long bones, limitation of joint motion, bowing of the long bones, osteopenia, and acetabular hypoplasia. Kyphoscoliosis, lumbar lordosis, platyspondyly, and cleft vertebrae.