Many parents of children with thumb dysplasia are asking this question because they just can’t figure out why their children are born with thumb dysplasia when their hands are fine. The cause of thumb dysplasia is not yet clear, and from our contact with children and parents of children with thumb dysplasia, we seldom see children with thumb dysplasia whose parents also have thumb dysplasia, so we believe that there is very little genetic association between thumb dysplasia and genetic predisposition. In many cases, the cause of thumb dysplasia is related to changes in the mother’s physical condition during early pregnancy and external factors, including the mother’s smoking or being exposed to secondhand smoke for a long period of time, which may lead to thumb dysplasia in the child.