The causes of facial elefting have been extensively investigated. The exact cause of elefting is unknown in most cases. Fdr most cleft conditions, no single factor can be identified as the cause. However, it is important to distinguish between isolated clefts (in which the patient has no other related health problem) and clefts associated with other birth disorders or syndromes. A syndrome is a set of physical, developmental, and sometimes behavioral traits that occur together. Clefts have been identified as a fear
ture ill over 300 syndromes, most of which are-rare.’ Syndromes account for approximately 15% of the total number of cases of cleft lip and cleft palate but nearly 50% of cases of isolated cleft palate. Medical geneticists are usually asked to consult with the family of children born with syndromes to identify the specific syndrome and to provide information to the parents about the likelihood of another child being affected. For nonsyndromic clefts, it was initially thought that heredity played a significant role in the causation. However, studies have been able to-implicate genetics Inonly 20% to 30% of cleft lip or palate patients. Even in those individuals whose genetic backgrounds may verify familial tendencies
for facial clefting, the mode of inheritance is not completely understood. It is not a simple case of mendelian dominant or recessive inheritance but is multigenetic. The majority of nonsyndromic clefts appear to be caused by’ an interaction between the individual’s genes (i.e., genetic predisposition) ant! certain factors in the environment that mayor may not be specifically identified. Environmental factors seem to playa contributory role at the critical time of embryologic development when the lip and palatal halves are fusing. A host of environmental factors have been shown in experimental animals to result in clefting. Tutritional deflciencies, radiation, several drugs, hypoxia, viruses, and vitamin excesses or deficiencies can produce clefting in certain situations. The risk for having another child with a cleft is based upon a number of factors that are often unique in a particular family. These include the number of family members
with clefts, how closely they are related, the race and sex of the affected individuals, and the type of cleft each person has. After a syndrome or complex disorder is excluded, recurrence ri~ counseling for a cleft can be
offered to families. No genetic test can determine a person’s individual chance of having a child with a cleft. Every parent has approximately a 1 in 700 risk of having a child with a cleft.’ Once parents have a child with
a cleft, the risk that the next child (and each succeeding child) will be affected is 2(Yt, to Sf){ (i.e.. 2 to 5 chances in lOO).1 If more than one person in the immediate family  has a cleft, the risk rises to 10% to ] 291) (i.e., roughly 1 chance in 10). i\. parent who has a cleft has a 2% to So/u chance that his or her child will have a cleft. If the parent with a cleft also has a close relative with a cleft, the risk increases to lorVi) to 12°1<) for their child being born with a cleft. The unaffected siblings of a child with a cleft
have an Increa ed risk of having a child with a cleft (1% or 1 in 100, compared with 1 in 700 when no history of cleft exists). If a syndrome is involved, the risk for recurrence within a family can be as high as 50%.1 Genetic counselors may be consulted for parents of children with
clefts or for people with clefts who would like to obtain more information on the relative risks for their offspring. In summary, orofacial elefts are produced by incompletely understood mechanisms, both genetic and environmental. With lack of complete knowledge of the causes, effective preventive measures, other than good prenatal practices (e.g., avoiding medications that are not absolutely necessary), are not available to prevent this deformity from developing.

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