Satoyoshi syndrome is a rare syndrome characterized by progressive, painful, intermittent muscle spasms. These muscle spasms usually start between 6-15 years old. Other symptoms of the syndrome may include diarrhea and an inability of the digestive tract to absorb certain foods, especially carbohydrates  (malabsorption). People affected by Satoyoshi syndrome may also have loss of hair on the head and body (alopecia universalis), short stature, and skeletal abnormalities. Women with Satoyoshi syndrome may not have a menstrual cycle (amenorrhea).  In all published cases, only one person in a family has Satoyoshi syndrome. This is even true when the person with Satoyoshi syndrome comes from a large family. Satoyoshi syndrome seems to be more common in Japan. The exact cause of the syndrome is unknown, but some researchers think it may be an autoimmune disease. Satoyoshi syndrome can be diagnosed when a doctor sees symptoms that are consistent with the syndrome. The diagnosis can be confirmed by a variety of laboratory tests. Treatment for Satoyoshi syndrome includes medication to suppress the immune system. 

Scientists don’t yet understand exactly what causes Satoyoshi syndrome, but research suggests that it is caused by the immune system mistakenly attacking cells in the nervous, gastrointestinal, and endocrine systems. Normally, our immune system protects our body by attacking and destroying disease causing bacteria and viruses, but during an autoimmune response, the immune system attacks healthy cells of its own body. About 60% of people with Satoyoshi syndrome have antinuclear antibodies in their bloodstream. These antibodies are produced by the immune system and attack the nucleus of cells throughout the body. Other people with Satoyoshi syndrome may have other antibodies as well, such as antibodies against glutamic acid decarboxylase (GAD). For people with Satoyoshi syndrome, it is thought that these antibodies target the nervous system, causing muscle spasms, and the gastrointestinal system, causing diarrhea and malabsorption. In some cases the antibodies may attack the hormone or endocrine system in women, causing amenorrhea. 

Symptoms of Satoyoshi syndrome typically begin between the age of 6-15 years and include painful muscle spasms, loss of hair on the scalp and body (alopecia universalis), and gastrointestinal problems such as diarrhea. The muscle spasms may worsen if left untreated. Gastrointestinal problems may also include an inability to absorb nutrients from food (malabsorption), especially carbohydrates. Women with Satoyoshi syndrome may not have a menstrual cycle (amenorrhea). People with Satoyoshi syndrome may have skeletal problems due to repeated injury to the bone caused by muscle spasms. Skeletal problems include pain and stiffness in the joints, bone cysts, and stress fractures. If the symptoms of Satoyoshi syndrome begin before a person has finished growing, the person may be shorter than other family members (short stature).

There is no cure for Satoyoshi syndrome, but treatments are available for the different symptoms a person may have. Medications that suppress the immune system may be used to help prevent the immune system from attacking the body. These medications may include corticosteroids. Certain medications may work better for some people than others, so a doctor may have to try different medications to find the exact combination that works best for each person.  In some cases, plasmapheresis has been shown to help improve symptoms of people with Satoyoshi syndrome who have not responded to other treatment options. 

The long-term outlook for people affected by Satoyoshi syndrome may vary. Some people with the syndrome respond well to treatment and symptoms may completely go away. Other people may not get better with current treatment options. Although women with Satoyoshi syndrome may have irregular menstrual periods, there have been reports of women with the syndrome who were able to become pregnant. Satoyoshi syndrome may be life-limiting due to worsening symptoms if treatment is not successful. Satoyoshi syndrome may also be life-limiting if a person with the condition suffers from mental health problems due to the symptoms causing challenges in daily living. 

A diagnosis of Satoyoshi syndrome is typically made based on a person having symptoms consistent with the syndrome. One research group suggests the diagnsosis of Satoyoshi syndrome may be based on a person having alopecia, muscle spasms, and gastrointestinal problems such as diarrhea.  A number of laboratory tests may also be completed to confirm the diagnosis of Satoyoshi syndrome. A doctor may recommend a blood test to look for antibodiesrelated to Satoyoshi syndrome. It may also be helpful to study how the muscles behave when they are spasming, so electromyography (EMG) may be recommended. Some reports also suggest that people with Satoyoshi syndrome have elevated levels of glycine in their cerebrospinal fluid (CSF), so a CSF collection may also be recommended. 

As is the case with most autoimmune diseases, there are no genetic changes that are known to cause or raise the risk of developing Satoyoshi syndrome. In general, scientists believe autoimmune disorders are caused by a combination of genetic and environmental factors, so often, especially in large families, more than one person has the autoimmune disease. But there have not been any reported cases of more than one family member having Satoyoshi syndrome. Therefore it is not clear if there are any inherited genetic factors that increase the risk of developing Satoyoshi syndrome.