**1. Introduction**

Orofacial cleft (OFC) anomalies may be unilateral or bilateral and involve the lip, the palate, or both. Due to similar phenotypic overlap and resulting health care needs of these patients, epidemiological studies usually group cleft lip, with or without cleft palate (CL/P), and cleft

and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

palate alone (CPO) even though the etiology of each may be unique. Whether or not CL/P and CPO have distinct etiology and should be combined in investigations is under debate.

It is often found in epidemiological studies that CL/P and CPO is considered underneath the umbrella of either "syndromic" or "nonsyndromic." Furthermore, "nonsyndromic" CL/P and CPO cases can be subgrouped into those that are isolated or those that have additional malformations that do not form a recognizable syndrome. Relatively, the etiology of nonsyndromic cases of CL/P and CPO is lesser known compared to those found identified with a syndrome. Due to the poorly characterized etiology of CL/P and CPO, in general, there is still debate for the best method of grouping CL/P and CPO in epidemiological studies, but the most common current classifications are used to help determine associations and thus help the clinician with their diagnosis and subsequent treatment.

The genetic basis for many syndromic cases of CL/P and CPO are well-described. Evidence for genetic factors underlying nonsyndromic CL/P and CPO has begun to materialize as well. While less well-described, it is also known that epigenetic modifications can play a role in the development of CL/P and CPO. Recently, the association between OFC and cancer has been explored, with evidence suggesting existence of a link between the presence of OFC in patients and risk of cancer in these patients and/or their families.
