Complex sentence: Basal ganglia dysfunction causes abnormal posturing of the limbs, trunk and face (dystonia) and upper brainstem disease results in impaired voluntary rapid eye movements (supranuclear gaze palsy).
Split into simpler sentences: Basal ganglia dysfunction causes abnormal posturing of the limbs, trunk, and face (dystonia). Upper brainstem disease results in impaired voluntary rapid eye movements (supranuclear gaze palsy).