Multifactorial means- dependent on a number of factors or causes. What we know about multifactorial conditions is that they are caused by a combination of environmental AND genetic factors. The genetic aspect may be due to several genes and their interactions with each other and the environmental factors are still often unknown in many cases.
Multifactorial conditions can “cluster” in families; the condition may occur more frequently in one family that you would expect and this is likely due to the genetic factors in that particular family.
There are many examples of multifactorial conditions, including neural tube defects such as spina bifida or anencephaly, congenital heart defects, cleft lip/palate, and many more. For these conditions, if one of your children has the condition, there will be a greater chance for future children to have it as well. Your doctor or genetic counselor can talk to you about specific chances depending on the condition and who in the family has it, etc.
For more information on specific multifactorial conditions, check out the side bar.