Review Question - QID 106977

A 25-year-old female presents to her geneticist due to the fear that she may have inherited her father's disease. He was diagnosed at the age of 41 when his symptoms of chorea, coordination problems, and cognitive decline begin to occur. He was diagnosed with a disease resulting from the expansion of CAG repeats on chromosome 4 and later developed severe dementia and died at the age of 56. The daughter was found to have double the amount of CAG repeats and was told by the geneticist that she may have an earlier onset with increased severity of disease. What phenomenon describes this?