Snyder-Robinson syndrome is an inherited condition that is characterized by intellectual disability, muscle and bone abnormalities, and other problems with development. It only occurs in males. Affected individuals have delayed development that begins in early childhood. Speech difficulties are common. Low muscle tone (hypotonia) and muscle mass leads to difficulty walking and an unsteady gait. Other features include thinning of the bones (osteoporosis), an abnormal curvature of the spine (kyphoscoliosis), and unusual facial features including a prominent lower lip, cleft palate, and facial asymmetry. Snyder-Robinson syndrome is caused by genetic changes in the SMS gene and is inherited in an X-linked recessive fashion.