Final answer:
Natalizumab use is associated with an increased risk of symptomatic infection of the central nervous system from the JC virus.
Step-by-step explanation:
Natalizumab use is associated with an increased risk of symptomatic infection of the central nervous system from the JC virus. The JC virus is a type of polyomavirus that can cause progressive multifocal leukoencephalopathy (PML) in immunocompromised individuals, such as those with multiple sclerosis who are being treated with natalizumab. PML is a serious and potentially fatal condition that affects the white matter of the brain.