Perhaps you should try some spelling variations:
"motor neuron disease" » "motor neutron disease", "motor neuro disease"
"motor neurons disease" » "motor neutrons disease", "motor neuros disease"
"motor neuronal disease" » "motor neutronal disease", "motor neuroal disease", "motor neural disease"
"motor neuros disease" » "motor neuro disease"

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (((("motor neuron disease") or ((("motor neurons disease") OR ("motor neuros disease"))))) or ("motor neuronal disease"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("motor neuron disease") OR ((("motor neurons disease") OR ("motor neuros disease"))))) OR ("motor neuronal disease")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"motor neuron disease\") or (((\"motor neurons disease\") OR (\"motor neuros disease\"))))) or (\"motor neuronal disease\"))".
• Removing quotes may allow a broader search: (((( motor neuron disease ) or ((( motor neurons disease ) OR ( motor neuros disease ))))) or ( motor neuronal disease )).
• Adding a wildcard symbol may retrieve word variants: (((("motor neuron disease") or ((("motor neurons disease") OR ("motor neuros disease"))))) or ("motor neuronal disease"))*.