Likely due to the complexity of<unk> , many theories have been provided over time in an attempt to define its origin. There is no definitive mechanism to explain its development but it is likely that there are interactions between genes and the environment resulting in improper development of the first and sometimes second brachial arch. Genetic<unk>  can be partially classified as a heritable autosomal dominant disease. The responsible mutation is found on the short arm of chromosome 1 in locations 32-34 (1p32-1p34). The mutation is heterozygous meaning that it only occurs in one allele. A single base substitution in the 11th coding region of the gene PTCH2 changes an adenine to guanine. This results in a valine being incorporated instead of an isoleucine at the 147th position during translation of the resulting transmembrane protein (Val147Ile). The transmembrane protein encoded by PTCH2 is 1204 amino acids long and is involved with inhibiting the sonic hedgehog signalling pathway that is involved with development. PTCH2 inhibits the smooth frizzled class receptor (SMO) which when active is responsible for increasing transcription rates of many genes involved with development and differentiation. PTCH2 (Val147Ile) is a loss of function mutation which results in a lack of control of cell growth during development and links it to<unk> .
Macrostomia
Microcoria
Microdontia
Acrania
Macrodontia 
Macrocephaly
Spotted lunulae
Oxycephaly