An investigator is studying the teratogenicity of cigarette smoking during pregnancy. He reviews several databases containing data about birth defects and prenatal drug exposures and finds that infants exposed to cigarette smoke in utero are approximately 2 times as likely to have a particular birth defect than unexposed infants. This defect results from abnormal development during the 6th week of gestation, when the maxillary prominences grow medially and fuse first with the lateral and then the medial nasal prominence. The defect is most likely which of the following?
The defect in question is a result of failure to fuse that is commonly seen in infants with Patau syndrome.
Cleft lip is caused by failure of fusion of the maxillary prominence with the medial nasal prominence.
Normally, children have two copies of GSTT1, a gene that is protective against the development of a cleft lip.
However, embryos with only one copy of this gene (e.g., in some European and Asian ancestry) have a 20-fold increase in developing a cleft lip if exposed to cigarette smoke in utero.