Clinical correlation congenital chromosomal and genetic abnormalities

Abstract

Advances in genetics, dating back to the careful observations of Gregor Mendel, have shed much light on the etiology of inherited diseases. However, with this progress has come a realization that many of these conditions do not follow simple patterns of traditionalMendelian inheritance, and therefore a continual reshaping of our understanding of genetic disorders has taken place. Genetic disorders can be grouped into those linked to a single gene (monogenic) or multiple genes (oligogenic and polygenic) and to those related to larger chromosomal abnormalities. Genetic disorders can be further complicated by phenotypic variability despite an identical genotype. For example, multiple family members may carry an identical gene mutation but demonstrate varying clinical phenotypes. This suggests a role for additional modifier genes or other factors that might affect the clinical phenotype. Anticipation is another phenomenon sometimes seen in genetic diseases, such as Huntington's disease. In this illness, offspring of affected individuals might experience the onset of disease symptoms at a younger age. This appears to result from an increase in size of a triplet repeat segment within the mutant gene from one generation to the next.