side of the nose, resulting in a cleft in one of the nasal halves. The nasal septum and cavity can be involved, though this is rare. Nasoschisis is also characterized by hypertelorism. Nasomaxillary dysplasia Nasomaxillary dysplasia is caused by a development arrest at the junction of the lateral side of the nose and the maxilla, which results in a complete or non-complete cleft between the nose and the orbital floor (nasoocular cleft) or between the mouth, nose and the orbital floor (oronasal-ocular cleft). The development of the lip is normal. Maxillary dysplasia Maxillary dysplasia can manifest itself on two different locations in the maxilla: in the medial or the lateral part of the maxilla. Median maxillary dysplasia is caused by a development failure of the medial part of the maxillary ossification centers. This results in secondary clefting of the lip, philtrum and palate. Clefting from the maxilla to the orbital floor has also been reported. Lateral maxillary dysplasia is caused by a development failure of the lateral part of the maxillary ossification centers, which also results in secondary clefting of the lip and palate. Clefting of the lateral part of the lower eyelid is typical for lateral maxillary dysplasia. Causes It is possible that facial clefts are caused by a disorder in the migration of neural crest cells. Another theory is that facial clefts are caused by failure of the fusion process and failure of inwards growth of the mesoderm. Other theories are that genetics play a part in the development of facial clefts or that they are caused by amniotic bands. Genetics Overview Around one in 700 individuals are born with craniofacial clefts. There are multiple genetic and environmental factors which contribute to craniofacial development. Within craniofacial disorders and abnormalities, orofacial clefts, and specifically cleft lip (CL) and cleft palate (CP) are the most common in humans. Occurrences of CL/P are most often (around seventy percent of cases) isolated and nonsyndromic, meaning they are not associated with a syndrome or inherited genetic conditions. Around thirty percent occur with other structural variances, and over 500 syndromes have been identified in which clefting is a principal feature. Clefting can result from teratogens, an agent that disrupts embryo development such as, radiation, maternal infection, chemicals, or drugs. Chromosomal abnormalities or mutations at single gene loci have also contributed to clefting development. Genetic causes are linked with most craniofacial syndromes, and CL/P and