Question

The disability to walk in a straight line is a symptom of what condition

Answer 1

It would be called a vestibular disorder or disability

Answer 2

Ataxia.

Ataxia is the loss of full control over your bodily movements. There are different kinds of ataxia.
People describe it as the lack of muscle coordination when a voluntary move is tried..
Symptoms:
Difficulty walking, you stagger.
Speech = slurred & slaw
Difficulty swallowing
Examples:
Difficulty using the hands and fingers to button shirts, or pick up a fork or spoon to eat. Writing, keyboarding, sewing, and playing an instrument can also be difficult.