agraphia vs brain disease

agraphia and brain disease both are nouns.

Word	Noun	Adjective	Verb	Adverb
agraphia	Yes	No	No	No
brain disease	Yes	No	No	No

As nouns, brain disease is a hypernym of agraphia; that is, brain disease is a word with a broader meaning than agraphia:

agraphia: a loss of the ability to write or to express thoughts in writing because of a brain lesion
brain disease: any disorder or disease of the brain

Other hypernyms of agraphia include brain disorder, encephalopathy.

agraphia (noun)	brain disease (noun)
a loss of the ability to write or to express thoughts in writing because of a brain lesion	any disorder or disease of the brain