From OMIM
Mirror movements are involuntary movements of a side of the body that mirror intentional movements on the opposite side. Mild mirror movements are physiologic in young children and gradually disappear within the first decade of life, likely due to maturation of the motor network. Mirror movements that persist beyond age 10 years represent a rare disorder usually showing autosomal dominant inheritance with incomplete penetrance (summary by Depienne et al., 2012). For a discussion of genetic heterogeneity of mirror movements, see MRMV1 (157600).  http://www.omim.org/entry/614508