Malformations have many causes. Chromosomal abnormalities account for approximately 25% of all causes, of which the most common autosomal trisomy of chromosomes 21, 18 and 13.
Another 20% are caused by monogenic mutations. Some defects are inherited as autosomal dominant traits, such as achondroplasia or waardenburg syndrome. Nevertheless, the majority of heterozygotes with congenital defects present a new genetic lethal mutation and, therefore, are often found as isolated cases in families.
Other syndromes malformations are inherited as autosomal or X-linked recessive manner, such as the syndrome of Smith-Lemley-Opitz syndrome or low, respectively. Causes approximately 50% of large congenital defects is unknown, but they are repeated in families with a higher frequency than would be expected based on population frequencies, and they are considered multifactorial diseases.
This category includes the well-identified congenital malformations of type of cleft lip with or without cleft palate and congenital heart defects.
The remaining 5% of defects considered caused by the action of certain environmental agents — medications, infections, chemicals or radiation, called teratogens (from the Greek. terato — beast and the gene — cause) due to their ability to cause birth defects