Three percent of full-term infants are born with a congential defect or disorder, and incidence is much higher in preterm infants and stillbirths. The defect may be a simple minor defect (such as an inguinal hernia) or a complex disorder involving many systems (such as Down syndrome). Down syndrome is the only common congenital; the other defects and disorders are rare or very rare, some having been reported fewer than 20 times worldwide. The causes of most are unknown. Chromosomal defects or abnormalities are known in some. Inheritance may be autosomal dominant, autosomal recessive or...