The Most Common Birth Defects

Other Genetic Causes

Birth defects sometimes have genetic causes such as Down syndrome and dwarfism. These are both sporadic birth defects but can be quite common in certain communities. Down syndrome is a genetic condition where the patient has both trisomy 21 or some other problem with their genes on chromosome 21, whereas dwarfism is associated with a mutation in the FGFR3 gene.

Trisomy 21 is when there is an extra copy of the 21st chromosome, where there are only supposed to be two copies of this chromosome, one inherited from both parents. It can be a complete copy or a partial copy, often causing Down syndrome. In dwarfism, the FGFR3 gene controls the growth of cells and the development of the embryo. When a person has two mutations in this gene, they tend to develop achondroplasia, which is a type of dwarfism where the limbs are abnormally short, and the size of the trunk is normal, while the head is unusually large.