Birth defects are conditions that are present at birth that cause mental or physical disability. They range from relatively mild and manageable to severe and life-threatening. A great number of them are genetic mutations of unknown causes. Others are well-studied syndromes whose genetic origins are meticulously documented and for whom advocacy groups have formed to support families and lobby for research.
The most familiar genetic birth defect is Down syndrome. Down syndrome occurs when a child receives an extra chromosome on chromosome 21. The use of the term syndrome indicates that there exists a multitude of physical and mental issues attached to the birth defect. Children with Down syndrome have facial and physical abnormalities as well as well as spinal, heart, and gastrointestinal issues. Less familiar genetic defects are trisomy 13 and trisomy 18 that, similar to Down syndrome cause physical and mental issues, but the extra chromosome resides on the 13th and 18th chromosomes.
Some birth defects involve the body's structure. Spina bifida occurs when a child's spine does not form properly during gestation. A child with cleft lip has a notch on the top lip that may or may not extend to the nose. Cleft palate causes a child to be born with a hole in the roof of his mouth that extends into the nasal cavity. Polydactyly causes extra fingers and toes.
Metabolic disorders involve the body's internal chemical processes and while they show few outward symptoms they have a major impact on a child's growth and development. Phenylketonuria prevents a child from processing phenylalanine and hypothyroidism prevents a child from producing adequate thyroxine. Both of these disorders can endanger a child's brain development and body growth and left untreated can have devastating consequences.
In the most tragic cases birth defects are 100% fatal. A child born without a brain has no chance of survival. The condition is anencephaly. The child may live hours or days but will always die. The same is true of holoprosencephaly, another condition involving the brain where the brain does not divide into two lobes and causes severe brain and facial abnormalities. Holoprosencephaly is an example of a birth defect that can occur by itself or be part of a birth defect syndrome.