Congenital Birth Defects Essay

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1.1 Congenital Birth Defects Birth defects, congenital abnormalities are terms used to describe developmental defects that are present at birth. There are a lot of genetic and environmental interactions in the complex transition from a fertilised ovum to a fully formed human being. The stage of development that the interactions are affected influences the type of birth defects. Birth defect causes can be divided into two types, genetic and environmental causes. There are also birth defects which are caused due to multifactorial inheritance (George, 2007). Genetic causes of birth defects It has been estimated that 25% of all birth defects are caused due to genetic factors and out of these 85% causes are known (Brent, 2004).…show more content…
There also occur chromosomal rearrangements which are of different types, such as translocation, inversions and insertions. Translocations represent the exchange of material between two non-homologous chromosomes. Chromosomal re-arrangements can be described as balanced or unbalanced. In balanced re-arrangements chromosome materials which have been lost or gained does not appear in the analysis under light microscope whereas in unbalanced re-arrangements chromosomes are either lost or gained which results in chromosomal imbalance. This type of balanced or unbalanced re-arrangements is associated with phenotypic abnormality like birth defects (Brent, 2004). Single gene mutations They account for 6% of birth defects and they represent malformations and affect multiple systems (Young, 2005). It is important to study the inheritance pattern of these birth defects to give the families accurate genetic advice. Autosomal dominant disorder is caused due to mutations in one allele of an autosomal gene whereas in the autosomal recessive disorder mutation happens in both the allele of an autosomal gene. X-linked recessive disorder is caused due to the mutation in the genes on the X chromosome. Males are more frequently affected as they only have one normal copy of the X-linked gene which becomes mutated unlike in females. X-linked dominant disorder is caused due to mutations in the X-chromosome
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