Which genetic disorder is characterized by neurodegeneration with symptoms typically appearing in adulthood?

Huntington's disease is a genetic disorder caused by a mutation in the HTT gene, which leads to neurodegeneration. This disorder is characterized by the progressive deterioration of nerve cells in the brain, resulting in a variety of motor, cognitive, and psychiatric symptoms. The symptoms of Huntington's disease typically begin to appear in adulthood, usually between the ages of 30 and 50, which distinguishes it from many other genetic disorders that may present symptoms at an earlier age.

In contrast, Marfan syndrome primarily affects connective tissue and presents symptoms that can occur at different ages, often during childhood or adolescence. Sickle-cell disease is a blood disorder that manifests early in life, typically presenting symptoms in infants or young children due to the effects on red blood cells. Tay-Sachs disease is a neurodegenerative disorder that generally appears in infancy, leading to severe neurological decline before the age of four.

The late onset of symptoms in Huntington's disease, therefore, is a key aspect that makes it the correct answer among the options provided.