ataxia vs neurological disease

ataxia and neurological disease both are nouns.

Word	Noun	Adjective	Verb	Adverb
ataxia	Yes	No	No	No
neurological disease	Yes	No	No	No

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

ataxia: inability to coordinate voluntary muscle movements; unsteady movements and staggering gait
neurological disease: a disorder of the nervous system

Other hypernyms of ataxia include nervous disorder, neurological disorder.

ataxia (noun)	neurological disease (noun)
inability to coordinate voluntary muscle movements; unsteady movements and staggering gait	a disorder of the nervous system