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"))))*.