Which of the following is true of Huntington's disease (HD)?
a. HD first appears in early childhood.
b. HD is caused by degeneration of the nigrostriatal bundle.
c. Stereotaxically-guided damage to the caudate and putamen is an effective treatment for HD.
d. HD is caused by a defective gene on chromosome 4.
e. A standard treatment of HD involves L-DOPA.