What is Segawa Syndrome?
Segawa syndrome, also called dopa-responsive dystonia, is an inherited disease that can cause physical rigidity and developmental delay. There are two forms: mild and severe.
In the mild form, symptoms typically begin in childhood. Children develop jerky movements that quickly progress to physical rigidity. These children show spastic movements, and make very little voluntary movement. If untreated, children with Segawa syndrome may have expressionless faces, drooping eyelids, tongue tremors, and drooling problems. They will show both intellectual and physical developmental delays. Some children with Segawa syndrome show a diurnal pattern, meaning their symptoms tend to be less severe early in the day and more severe late in the day. With early treatment, children with Segawa syndrome can avoid many or all of the disease’s symptoms.
The severe form of the disease will appear in infancy, usually before six months of age. Affected infants have delayed motor skills, weakness in the chest and abdomen, rigidity in the arms and legs, and problems with movement. These children will eventually have learning disabilities, problems with speech, and behavioral/psychological problems. In addition, some people with the disease have problems with their autonomic nervous system, which regulates unconscious functions such as body temperature regulation, digestion, blood sugar level, and blood pressure. Treatment of the severe form of the disease is often less successful.
Segawa syndrome is caused by a deficiency in an enzyme called tyrosine hydroxylase. Without it, the amino acid tyrosine cannot properly be converted to dopamine, a key neurotransmitter in the brain. Dopamine is important for many functions, including muscle control and cognition.
Note that there is another type of Segawa syndrome with a different genetic basis that is not addressed here.
How common is Segawa Syndrome?
The prevalence of Segawa syndrome is unknown, and only a small number of cases have been diagnosed globally. Cases have been reported in Japan and in the Netherlands.
How is Segawa Syndrome treated?
Individuals with the mild form of Segawa syndrome respond well to treatment with supplements of L-dopa and carbidopa. If taken before symptoms appear, the symptoms may be avoided completely. Even if symptoms have already begun, children with the disease often respond extremely well to the medication. If the disease has gone untreated for some time, certain symptoms may remain, including an irregular gait and other mild movement and speech difficulties.
Treatment with L-dopa and carbidopa supplements has been less beneficial for individuals with severe Segawa syndrome, but this treatment may improve motor skills over time.
If symptoms have gone untreated, physical, occupational, and/or speech therapists may prove helpful.
What is the prognosis for a person with Segawa Syndrome?
With early and consistent treatment, the prognosis for a person with mild Segawa syndrome is good. Many symptoms can be reversed with treatment. If treatment is not begun early and/or the course of the disease is severe, the person may be shorter than they would otherwise have been and may have an irregular walk and/or learning disabilities.