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. Environmental Interaction Craniofacial disorders have high variance in phenotypic expression, and researchers have suggested this variance could be due to interactions between the mutated/deviated genes and other genes, along with interactions with environmental factors. Environmental causes have been found to contribute to craniofacial clefting, however, these are still influenced by and supported by genetic factors. Many studies, for example, have linked maternal smoking to increased CLP risk; however, the increased risk suggests that genes in metabolic pathways could still contribute to susceptibility or formation of CL/P. Development and Inheritance The craniofacial complex begins its progress in the fourth week of development, and results from neural crest cells migrating to form and fuse the facial primordia. Failures or deviations in this process result in craniofacial clefts, either CL or CP. The range of variation in phenotype aligns with ancestry. Studies have found increased amounts of clefting in the relatives of patients with clefts, suggesting genetic factors are the underlying cause for CL/P. Inheritance has a known and significant role in human craniofacial morphology. This is supported through cephalometric and anthropometric comparisons of family members including between triplets, twins, siblings, and parents and children. Genetic Experimentation Genetic factors of craniofacial clefting can be investigated and tracked through several methods including sequencing in humans, Genome-wide association studies (GWAs), fate mapping, expression analysis, and animal studies (knockout experiments or models with clefting from chemical mutagenesis). Twin studies and familial clustering have also revealed that facial structure and formation are genetically linked. 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