Amyotrophic lateral sclerosis (als), the disease that prompted more than two million people to perform the ice bucket challenge, is caused by the excess production of which amino acid?

Glutamate

Explanation:

Amyotrophic lateral sclerosis is a disease which is caused by the death of the neurons which control the voluntary muscles of the body especially the motor neurons. The neurons die when the calcium level increases and the capacity of the transporter which removes the glutamate from the neuron called amino acid transporter 2 decreases. Therefore the increased level of the glutamate in the neurons causes the death of the neurons.

The disease is caused by either some environmental factors and in some cases it becomes genetically inherited.  

Thus, glutamate is the correct answer.