There are several factors that may increase the risk of having a child with cleft lip and palate. While the inheritance of many genes from either parent and the maternal use of certain medications and substances (maternal smoking, anticonvulsants, alcohol, retinoic acid) are believed to increase the risk of having a child with a cleft, the majority of children born with a cleft of the lip or palate have none of these associated factors.
The way that the inheritance of many genes can affect the risk for having cleft of the lip or palate is difficult to understand. A simplified way to think about it is that there are many genes that slightly increase someone’s risk of having a cleft. The more of these genes a person has, the more likely it is that they will have a cleft. However, it is important to understand that in most cases, a family with a parent or child with a cleft still has a low risk of having more children with clefts of the lip and palate.
The most common scenario is that a family will have a child born with a cleft and no other history of a person with cleft lip and palate in either parent’s family. The risk of this family’s next child having a cleft is about 5% (1 in 20). If a family has one parent with a cleft but no children with a cleft, the risk of their next child having a cleft is about 5% (1 in 20). If a family has no parent with a cleft but two children born with clefts, the risk of their next child having a cleft is about 10% (1 In 10). If a family has one parent and one child with a cleft, the risk of their next child having a cleft approaches 20% (1 in 5). In other words, a family with one parent and one child born with a cleft has an 80% (4 in 5) chance of their next child NOT being born with a cleft. So even when several family members have had a cleft, the risk is higher than the average person, but still relatively low.
There are rare exceptions to this such as Van der Woude syndrome, which demonstrates autosomal dominant inheritance where 50% of a family’s children may be born with a cleft. For this reason, genetic testing should be done when there is a strong family history of clefts