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 other orofacial clefts are recognized as heterogeneous disorders, meaning there are multiple recognized causes. Orofacial clefts have great phenotypic diversity, and their associated genetic environments have called for vast research and investigation.
Several genes have been associated with craniofacial disorders through experimentation, including sequencing Mendelian clefting syndromes. Over 25 loci have been identified as potential influencers of craniofacial clefts across populations. Linked Genes
The transforming growth factor (TGF) family has provided multiple candidate genes linked with craniofacial development and malformation. TGF is involved in cell migration, differentiation, and proliferation, as well as regulating the extracellular matrix. Another gene that has been flagged as causal for craniofacial disorders, including CL/P, is interferon regulatory factor 6 or, IRF6. Mutations in IRF6 cause Van der Woude syndrome, the most common clefting syndrome. Ventral anterior homeobox 1, VAX1, and noggin, NOG, were identified with genome-wide significance for contributing to CL/P. Additionally, mutations in SPECC1L have recently been identified as influential to facial structure formation, and as causal for syndromic facial clefting. Nonsyndromic CL/P has been associated with the transcription factor forkhead box protein E1 (FOXE1), as mutations have resulted in cases of CL/P in mice. Other genes which have been found to interact with or contribute to craniofacial clefting include FGFRs, TWIST, MSXs, GREM1, TCOF1, PAXs, MAFB, ABCA4, and WNT allowing great cause for more research into the genetic basis for craniofacial disorders. Prevention
Because the cause of facial clefts still is unclear, it is difficult to say what may prevent children being born with facial clefts. It seems that folic acid contributes to lowering the risk of a child being born with a facial cleft.