Dopamine transporter deficiency syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Dopamine transporter deficiency syndrome is a rare movement disorder. The condition is also known as infantile parkinsonism-dystonia because the problems with movement (dystonia and parkinsonism, described below) usually start in infancy and worsen over time. However, the features of the condition sometimes do not appear until childhood or later.

People with dopamine transporter deficiency syndrome develop a pattern of involuntary, sustained muscle contractions known as dystonia. The dystonia is widespread (generalized), affecting many different muscles. The continuous muscle cramping and spasms cause difficulty with basic activities, including speaking, eating, drinking, picking up objects, and walking.

As the condition worsens, affected individuals develop parkinsonism, which is a group of movement abnormalities including tremors, unusually slow movement (bradykinesia), rigidity, and an inability to hold the body upright and balanced (postural instability). Other signs and symptoms that can develop include abnormal eye movements; reduced facial expression (hypomimia); disturbed sleep; frequent episodes of pneumonia; and problems with the digestive system, including a backflow of acidic stomach contents into the esophagus (gastroesophageal reflux) and constipation.

People with dopamine transporter deficiency syndrome may have a shortened lifespan, although the long-term effects of this condition are not fully understood. Children with this condition have died from pneumonia and breathing problems. When the first signs and symptoms appear later in life, affected individuals may survive into adulthood.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

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.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

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.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Dystonia · Very frequent (99-80%)

An abnormally increased muscular tone that causes fixed abnormal postures. There is a slow, intermittent twisting motion that leads to exaggerated turning and posture of the extremities and trunk.

Parkinsonism · Very frequent (99-80%)

Characteristic neurologic anomaly resulting from degeneration of dopamine-generating cells in the substantia nigra, a region of the midbrain, characterized clinically by shaking, rigidity, slowness of movement and difficulty with walking and gait.

Abnormal pyramidal sign · Frequent (79-30%)

Functional neurological abnormalities related to dysfunction of the pyramidal tract.

Abnormality of carboxylic acid metabolism · Frequent (79-30%)

Any deviation from the normal concentration of carboxylic acid in the blood circulation.

Absent speech · Frequent (79-30%)

Complete lack of development of speech and language abilities.

Axial hypotonia · Frequent (79-30%)

Muscular hypotonia (abnormally low muscle tone) affecting the musculature of the trunk.

Bradykinesia · Frequent (79-30%)

Bradykinesia literally means slow movement, and is used clinically to denote a slowness in the execution of movement (in contrast to hypokinesia, which is used to refer to slowness in the initiation of movement).

Cerebral palsy · Frequent (79-30%)

Cerebral palsy describes a group of permanent disorders of the development of movement and posture, causing activity limitation, that are attributed to nonprogressive disturbances that occurred in the developing fetal or infant brain. The motor disorders of cerebral palsy are often accompanied by disturbances of sensation, perception, cognition, communication, and behavior, by epilepsy, and by secondary musculoskeletal problems.

Other findings in the same source

From: Orphanet

Additional reported features include Chorea (Frequent (79-30%)); Constipation (Frequent (79-30%)); Feeding difficulties (Frequent (79-30%)); Gastroesophageal reflux (Frequent (79-30%)); Global developmental delay (Frequent (79-30%)); Hypertonia (Frequent (79-30%)); Hypokinesia (Frequent (79-30%)); Hypomimic face (Frequent (79-30%)); Irritability (Frequent (79-30%)); Oculogyric crisis (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Dopamine transporter deficiency syndrome is Neurology, with a neurologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which nervous-system findings help explain the symptoms?
• Would an assessment of walking, communication or daily function be helpful?
• Are rehabilitation or other specialist services relevant?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Dopamine transporter deficiency syndrome. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.