Congenital abnormality
From Wikipedia, the free encyclopedia
| Congenital abnormality Classification and external resources |
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| MeSH | D000013 |
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A congenital abnormality (congenital malformation, birth defect) is a condition which is present at the time of birth which varies from the standard presentation.[1]
It is a type of congenital disorder which is primarily structural in nature.[2]
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[edit] Types
A limb malformation is called a dysmelia. These include all forms of malformations of limbs, such as amelia, ectrodactyly, phocomelia, polymelia, polydactyly, syndactyly, polysyndactyly, oligodactyly, brachydactyly, achondroplasia, congenital aplasia or hypoplasia, amniotic band syndrome, and cleidocranial dysostosis.
Congenital malformations of the heart include patent ductus arteriosus, atrial septal defect, ventricular septal defect, and tetralogy of fallot. Helen Taussig has been a major force in research on congenital malformations of the heart.[1]
Congenital malformations of the nervous system include neural tube defects such as spina bifida, meningocele, meningomyelocele, encephalocele and anencephaly. Other congenital malformations of the nervous system include the Arnold-Chiari malformation, the Dandy-Walker malformation, hydrocephalus, microencephaly, megencephaly, lissencephaly, polymicrogyria, holoprosencephaly, and agenesis of the corpus callosum.
Congenital malformations of the gastrointestinal system include numerous forms of stenosis and atresia, and imperforate .
[edit] Occurrence rate
About 3% of newborns have a "major physical anomaly", meaning a physical anomaly that has cosmetic or functional significance.[3]
Congenital malformations involving the brain are the largest group at 10 per 1000 live births, compared to heart at 8 per 1000, kidneys at 4 per 1000, and limbs at 1 per 1000. All other physical anomalies have a combined incidence of 6 per 1000 live births.
Congenital malformations of the heart have the highest risk of death in infancy, accounting for 28% of infant deaths due to birth defects, while chromosomal abnormalities and respiratory abnormalities each account for 15%, and brain malformations about 12%.
[edit] Causes
The cause of 40-60% of congenital physical anomalies (birth defects) in humans is unknown. These are referred to as sporadic birth defects, a term that implies an unknown cause, random occurrence regardless of maternal living conditions,[4] and a low recurrence risk for future children. For 20-25% of anomalies there seems to be a "multifactorial" cause, meaning a complex interaction of multiple minor genetic abnormalities with environmental risk factors. Another 10-13% of anomalies have a purely environmental cause (e.g. infections, illness, or drug abuse in the mother). Only 12-25% of anomalies have a purely genetic cause. Of these, the majority are chromosomal abnormalities.[5]
Genetic causes of congenital anomalies include inheritance of abnormal genes from the parents, as well as new mutations in one of the germ cells that gave rise to the fetus.
Environmental causes of congenital anomalies are referred to as teratogenic. These are generally problems with the mother's environment. Teratogens can include dietary deficiencies, toxins, or infections. For example, dietary deficiency of maternal folic acid is associated with spina bifida. Ingestion of harmful substances by the mother (e.g, alcohol, mercury, or prescription drugs such as phenytoin) can cause recognizable combinations of birth defects.
Several infections which a mother can contract during pregnancy can also be teratogenic. These are referred to as the TORCH infections.
[edit] Teratogens
The greatest risk of a malformation due to environmental exposure to a teratogen (terato = monster, gen = producing) between the third and eighth week of gestation. Before this time, any damage to the embryo is likely to result in fatality, and the baby will not be born. After eight weeks, the fetus and its organs are more developed and less sensitive to teratogenic incidents.
The type of birth defect is also related to the time of exposure to a teratogen. For instance, the heart is susceptible from three to eight weeks, but the ear is susceptible from a slightly later time to about twelve weeks.
Many common skin care ingredients can be absorbed through the skin in small amounts, where they can enter the bloodstream and pass into baby's circulation.[citation needed]
Infection in the mother early in the third week may damage the heart. An infection in the eleventh week is less likely to damage the heart, but the baby may be born deaf. A common cause of congenital deafness of children in particular is a measles infection in the mother.
[edit] References
- ^ Penn State Plastic Surgery: Hand & Wrist Surgery: Congenital Abnormalities.
- ^ MeSH Congenital+Disorders
- ^ Kumar, Abbas and Fausto, eds., Robbins and Cotran's Pathologic Basis of Disease, 7th edition, p.470.
- ^ Bezerra Guimarães MJ, Marques NM, Melo Filho DA (2000). "[Infant mortality rate and social disparity at Recife, the metropolis of the North-East of Brazil]" (in French). Sante 10 (2): 117–21. PMID 10960809.
- ^ Kumar, Abbas and Fausto, eds., Robbins and Cotran's Pathologic Basis of Disease, 7th edition, p.473.
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