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Birth defects: Causes

Carlos A Bacino, MD, FACMG
Section Editors
Helen V Firth, DM, FRCP, DCH
Louise Wilkins-Haug, MD, PhD
Deputy Editor
Elizabeth TePas, MD, MS


A birth defect is any structural anomaly present at birth. These defects can be caused by genetic abnormalities and/or environmental exposures, although the underlying etiology is often unknown [1]. Birth defects can be isolated or present in a characteristic combination or pattern that may affect one or more organ systems. A genetic disorder or genetic abnormality is caused by a change or mutation in the genome that often leads to a medical consequence. Even though most genetic disorders are congenital, they can have a delayed clinical presentation or even adult onset. These disorders can be inherited or the result of a new mutation.

This topic discusses the causes of birth defects. The epidemiology, types, patterns, and evaluation of birth defects are discussed in detail separately, as are specific congenital anomalies. (See "Birth defects: Epidemiology, types, and patterns" and "Birth defects: Approach to evaluation".)


The causes of congenital anomalies are genetic and nongenetic [2].

Genetic abnormalities include:

Chromosomal disorders (eg, Down syndrome) (see "Down syndrome: Overview of prenatal screening" and "Down syndrome: Clinical features and diagnosis")

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Literature review current through: Nov 2017. | This topic last updated: Dec 04, 2017.
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