Abnormal Growth and Development
Major congenital anomalies occur in 2%–3% of live births. Causes include chromosomal abnormalities, multifactorial disorders, and environmental agents, but many cases are idiopathic. Regardless of etiology, congenital anomalies may be categorized as shown in Table 15-2.
A malformation implies a morphologic defect present from the onset of development or from a very early stage. A disturbance to a group of cells in a single developmental field may cause multiple malformations. Multiple etiologies may result in similar field defects and patterns of malformation. A single structural defect or factor can lead to a cascade, or domino effect, of secondary anomalies called a sequence. The Pierre Robin group of anomalies (cleft palate, glossoptosis, micrognathia, respiratory problems) may represent a sequence caused by underdevelopment of the mandible and is seen in disorders such as Stickler and fetal alcohol syndromes. A syndrome is a recognizable and consistent pattern of multiple malformations known to have a specific cause, which is usually a mutation of a single gene, a chromosome alteration, or an environmental agent. An association represents defects known to occur together in a statistically significant number of patients. An association may represent a variety of yet-unidentified causes. Two or more minor anomalies in combination significantly increase the likelihood of an associated major malformation.
Table 15-2 Types of Congenital Anomalies
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.