Genetics and Genomics of Congenital diseases
Virtually any disease is the result of the combined action of genes and environment, but the relative role of the genetic component may be large or small. Among disorders caused wholly or partly by genetic factors, three main types are recognized : chromosome disorder, single-gene defect, multifactorial disease with complex inheritance.
In chromosome disorders, the defect is due to an excess or deficiency of genes located on entire chromosomes or chromosome segments. Single-gene defects are caused by pathogenic mutations in individual genes. The mutation may be present on both chromosomes of a pair or on only one chromosome of a pair. Single-gene defects often cause diseases that follow one of the classic inheritance patterns in families, autosomal recessive, autosomal dominant, or X-linked. Most such defects are rare, but single-gene disorders as a group are responsible for a significant proportion of disease and death. Multifactorial disease with complex inheritance describes the majority of diseases in which there is a genetic contribution, as evidenced by increased risk for disease in identical twins or close relatives of affected individuals, and yet the family history does not fit the inheritance patterns seen typically in single-gene defects. There appears to be no single error in the genetic information in many of these condition.
Genetic counselors define and address the complex psychosocial issues associated with a genetic disorder in a family and provide psychologically oriented counseling to help individuals adapt and adjust to impact and implications of the disorder in the family. For this reason, genetic counseling may be most effectively accomplish through periodic contact with the family. In this article, I describe how genetics and genomics are applied to medical today.
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