A 35 year-old black male is seen in clinic with 3 month history of weakness and muscle cramps, first felt in the left arm but progressing to both legs. His voice is not as loud as it used to be, and is a little hoarse. He has no sensory loss. Reflexes are brisk, including a jaw jerk. The toes are equivocal.
Fasciculations are present in the tongue at rest, and all four proximal extremities.
One year later he has difficulty swallowing, is short of breath and appears emaciated. A 62 year-old woman complains of pain and numbness of the hand. She has been dropping objects from the hand, but the discomfort is worse at night. A 16 year-old woman is referred to you by her psychiatrist. For the last year she has complained of weakness which came on after the death of her father.