Mirror Movement Disorder

What if you wanted your right hand to pick up a pencil and suddenly your left hand reached out as well? What if you tried to pick up a sock with the toes of your left foot and your right foot also reacted? These are examples of mirror movement disorder. Recent research with genetically engineered mice may have clues to what causes this puzzling phenomenon.

Definition

• The symptoms of mirror movement disorder are pretty much what the name implies. When a person with this disorder moves his right hand, his left hand mirrors the movement, carrying out the same motion (though usually to a lesser extent) as the intended hand. This behavior is often present in babies and in children up to 10 years of age, but once hemisphere-specific motor movements have developed, mirror movement is only seen in people with neurological disorders or deficits. People with mirror movement disorder have reported difficulty in playing the piano, typing and other instances in which each hand must do something completely different from the other.

History

• Mirror movement disorder (MM) was first noted in 1879, but a formal definition was not compiled until 1991. A 2008 Letter to the Editor of Neurology India gives a description of a Persian family that has displayed mirror movement disorders for five generations. All family members studied had normal psychological and neurological tests, as well as cervical and brain MRIs, though mirror movements were observed in these family members since they were children. This suggests that the cause of MM in this family was both hereditary and of an origin other than the typical neurological disorders diagnosed by the tests administered.

Associated Disorders

• Mirror movement disorder has been linked to Parkinson's disease, cerebral palsy, symptomatic epilepsy, spina bifida, obsessive-compulsive disorder, schizophrenia, and other neurological and psychological conditions. It is unclear whether the disorder is caused by these diseases or that some intervening variable--perhaps a decrease in some vital neurotransmitter, protein, or enzyme brought on by these diseases--is causing this odd motor behavior.

Case Study

• A Singapore Medical Journal article in 2002 discussed the case of a Chinese military recruit who was unable to pass his physical requirements because attempts to navigate the monkey bars proved impossible. He could grasp the starting bar with both hands, but letting go of one hand to swing to the next bar resulted in both hands letting go no matter how hard he tried. Although this 20-year-old's legs were not affected, his father, also subject to these mirror movements, could not pick up a bead with his right foot without his left foot mirroring the same movement. Though both men had displayed these behaviors their entire lives, the father reported that his symptoms had diminished after reaching 35 years of age.

Research on Mice

• In 2001, Dr. Mark Henkemeyer, a researcher at the University of Texas Southwestern Medical Center, genetically engineered mice so they no longer had the protein Ephrin-B3. This lack of Ephrin-B3 caused the mice to exhibit odd motor behaviors. When the mice attempted to walk, both back legs moved together to hop instead of walk. The Henkemeyer study suggests this protein plays a role in directing messages from the brain to the spinal cord and then to the side of the body in which the messages are intended to cause an action. If Ephrin-B3 is absent, the spinal cord will allow messages to pass to both sides of the body and unintentional mirror movements will result.