Learning how to use our hands and establishing dexterity is a vital skill that helps us to navigate our environment with precision. Sometimes, however, this development gets interrupted leading to movement disorders such as mirror movement, where intentional movements by one side of the body are mirrored involuntarily by the other. For example, everything one hand does the other one copies.
Mirror movement is a rare and poorly understood disorder, but a case study published in the journal BMJ Case Reports has described a 13-year-old patient in India who has the condition. Most unusually, however, the patient constituted the first known case of mirror movement in a person with Turner Syndrome, a chromosomal condition that affects only females as a result of one of the two XX chromosomes being either partially or completely missing. It can impact ovarian function depending on the specific karyotype involved causing subsequent amenorrhea, as well as heart defects and stunted growth. The first-of-its-kind case study has raised questions among the medical community as to if or how the two conditions could be connected.
The disorder is seen in around 1 in a million children, and the exact cause or causes of mirror movement remain unclear. There has been some speculation as to whether false synapses forming in areas of the brain could be to blame. Investigations into patients with mirror movement have revealed around a third exhibit gene mutations with more than one gene involved. The mutations cause impaired development of the nervous system, which leads to messages from the brain going to both sides of the body.
The patient first presented with an absence of periods and based on clinical features of mild dysmorphism, including short stature and absent secondary sex characteristics was diagnosed with Turner Syndrome, but during a clinical visit it was noticed that her hands were moving in an unusual way. As the video above illustrates, the symptom she was experiencing was mirror movement as when using one hand to count, her other hand would move in the same way. Involuntary movements following a voluntary one are known as synkinesia and are usually associated with neurological conditions such as cerebral palsy, Klippel-Feil syndrome, and types of Parkinson's, but the patient's neurological examinations including an MRI of her brain were all normal.
Kallmann syndrome is another condition that has been found in patients exhibiting mirror movement though its exact connection to the disorder is also unclear. It falls within a family of endocrine diseases that are influenced by hormones. Turner syndrome is a genetic disorder but certain karyotypes can influence ovarian function and hormone levels. However, the researchers state that in this case there was no evidence which indicated that Turner Syndrome and mirror movement were anything more than incidental findings with no causal relationship, but further investigations may have revealed connection were resources not limited.