Individuals with premutation length repeats in FMR1 may have some of the phenotypes of Fragile X but not others, which is ______
_______; for example, some individuals may have cognitive deficiencies, while others might have late onset ataxia. In addition, some individuals will have no phenotypes of the condition at all, due to ____________.
In genetics, variable expressivity refers to the fact that individuals having the same alleles/genes/genotype associated with a particular genetic condition may exhibit different clinical features of this condition. In general, variable expressivity is due to the combination of both genetic and environmental factors. An example of variable expressivity is the Marfan syndrome, where all individuals with this disorder have a dominant mutation in the FBN1 (fibrillin 1) gene and show different degrees of the same phenotype. Moreover, incomplete penetrance (also known as reduced penetrance) refers to the complete absence of a genetic trait or disease in individuals having alleles/genes/genotype associated with the condition. In consequence, individuals with incomplete penetrance do not develop features of the disease. An example of incomplete penetrance is given by those individuals with mutations in BRCA1/BRCA2 genes (associated with an increased risk of developing breast cancer) that do not develop cancer.
