Mirror-image unilateral condylar hyperplasia in monozygotic twins.

Unilateral condylar hyperplasia (UCH) is an abnormal growth process that results in the development of mandibular asymmetry. The aetiopathogenesis of this entity is still unclear. Various factors including hormonal influences, intrauterine factors, trauma, infection, and genetics have been speculated to lead to the development of UCH. In genetic epidemiology, twins have been a valuable resource for investigating the genetic basis of complex traits and diseases. We present a case of mirror-image UCH in a pair of monozygotic twins, providing evidence of a possible genetic link for this mandibular growth disorder. The concordance in the monozygotic twins appears to be reflected by the precise mirror-image presentation of the congenital dentofacial anomalies. Further twin studies would be useful in clarifying the contributions of genetic and environmental factors to the presence and development of UCH.