Dopamine transporter deficiency syndrome appears to be a rare disease; only about 20 affected individuals have been described in the medical literature. Researchers believe that the condition is probably underdiagnosed because its signs and symptoms overlap with cerebral palsy and other movement disorders.

Dopamine transporter deficiency syndrome is caused by mutations in the SLC6A3 gene. This gene provides instructions for making a protein called the dopamine transporter. This protein is embedded in the membrane of certain nerve cells (neurons) in the brain, where it transports a molecule called dopamine into the cell. Dopamine is a chemical messenger (neurotransmitter) that relays signals from one neuron to another. Dopamine has many important functions, including playing complex roles in thought (cognition), motivation, behavior, and control of movement.

Mutations in the SLC6A3 gene impair or eliminate the function of the dopamine transporter. The resulting shortage (deficiency) of functional transporter disrupts dopamine signaling in the brain. Although dopamine has a critical role in controlling movement, it is unclear how altered dopamine signaling causes the specific movement abnormalities found in people with dopamine transporter deficiency syndrome.

Studies suggest that the age at which signs and symptoms appear is related to how severely the function of the dopamine transporter is affected. Affected individuals who develop movement problems starting in infancy most often have transporter activity that is less than 5 percent of normal. Those whose movement problems appear in childhood or later tend to have somewhat higher levels of transporter activity, although they are still lower than normal. Researchers speculate that higher levels of transporter activity may delay the onset of the disease in these individuals.