Congenital deformities and disorders are either:
- attributable to faulty genetic information which affects the development of the foetus and shows at birth or in early childhood; the malformation may be inherited (be familial) or arise spontaneously in the individual egg, sperm or embryo;
- or arising from inherited genetic information from other internal or external factors, such as hormonal disturbance, drugs, toxins and mutagens (collectively called teratogens) and physical injury.
Types of common congenital anomalies include atresia (a normal opening or tube in the body is closed or absent), stenosis (abnormal narrowing of a bodily canal or passageway), malpositioning, malformation, discolouration or absence of an organ. Cysts, and accessory or multiple organs occur. Organs may show congenital malfunction.