[stevewoods]

Your question about distinguishing between ALS and Alzheimer's disease is appreciated. Very few people tend to ponder over this. It is a fact that ALS and Alzheimer's (and almost every neurodegenerative disease) share quite a lot of common features. 

Following are some intriguing similarities between almost every neuro-degenrative disease (be it ALS/Alzheimer's/Parkinson's):

Increased instances of protein misfolding, with marked decrease in recycling. This leads to accumulation of potentially toxic proteins/structures.

Misfolded proteins tend to spread from cell to cell, leading to a sort of spreading of degeneration.

Increased Neuro-inflammation.

But at the level of symptoms, one can easily distinguish ALS from Alzheimer's:
Alzheimer's is more a dysfunction of memory associated skills, which includes loss of memory, difficulty in concentration, mood swings, difficulty in solving regular tasks/problems, confusion with time/places/relationships. On the other hand, ALS is more associated with movement/co-ordination problems like Difficulty walking, tripping or difficulty doing the normal daily activities (in terms of ability to move). Weakness of leg/feet/ankles, trouble in swallowing/speaking, muscle cramps/twitches etc.

Is Alzheimer's Inherited?

The answer is "YES" and "NO"

Whereas early onset Alzheimer's is inheritable, late onset Alzheimer's isn't that inheritable (it's more age associated)