Which condition is caused by a deficiency of dopamine in the striatum due to degeneration of neurons in the substantia nigra?

Parkinson's disease is a neurodegenerative disorder characterized by the loss of dopamine-producing neurons in the substantia nigra, a critical area of the brain involved in movement control. The striatum relies on adequate levels of dopamine to facilitate smooth and coordinated motor function. When there is a deficiency of dopamine due to neuronal degeneration, individuals typically experience symptoms such as tremors, rigidity, bradykinesia (slowness of movement), and postural instability.

In contrast, Huntington's disease is caused by genetic mutations leading to the degeneration of both the striatum and other brain regions but is not specifically linked to dopamine deficiency. Alzheimer's disease involves the accumulation of amyloid plaques and tau tangles, leading to cognitive decline, and doesn't primarily stem from dopamine-related mechanisms. Multiple sclerosis is an autoimmune disorder affecting the central nervous system, resulting in demyelination rather than direct neurodegeneration of the substantia nigra or dopamine pathways.

Consequently, the hallmark features associated with Parkinson's disease and the direct relationship between dopamine deficiency and symptoms uniquely identify it as the correct answer in this context.