Genetics of microtia and associated syndromes

Microtia is a congenital anomaly, characterised by a small, abnormally shaped auricle (pinna). It is usually accompanied by a narrow, blocked or absent ear canal. Microtia can occur as the only clinical abnormality or as part of a syndrome. The estimated prevalence of microtia is 0.8-4.2 per 10 000 births, and it is more common in men. Microtia can have a genetic or environmental predisposition. Mendelian hereditary forms of microtia with an autosomal dominant or recessive mode of inheritance, and some forms due to chromosomal aberrations have been reported. Several responsible genes have been identified, most of them being homeobox genes. Mouse models have been very useful to study these genes, providing valuable information on the development of the auditory system. In this article, we review the epidemiological characteristics of microtia and the environmental causes involved. In addition, we discuss the development of the auditory system, specifically the relevant aspects of external and middle ear development. The focus of this review is to discuss the genetic aspects of microtia and associated syndromes. The clinical aspects of various disorders involving microtia are also discussed in relation to the genes that are causing them.