A Study to Learn About the Safety of BIIB080 Injections and Whether They Can Improve Symptoms of Participants With Mild Cognitive Impairment Due to Alzheimer's Disease (AD) or Mild AD Dementia Between 50 to 80 Years of Age

This study is looking for people aged between 50 and 80. To join, you would need to have been diagnosed with mild memory problems due to Alzheimer's disease or mild Alzheimer's dementia.

Doctors would check your memory and thinking abilities carefully using specific tests to make sure your symptoms fit the study requirements. You would also need to show signs of Alzheimer's disease in your brain, which they can check through scans or by looking at your spinal fluid.

It's important that you have a care partner, such as a family member or close friend, who spends at least 10 hours a week with you. This person would help the study team understand how your memory and daily activities are changing. If you've been taking other Alzheimer's medications, you'd need to have been on a stable dose for at least eight weeks before joining.

If you decide to take part, the study will last about four years in total. It starts with an initial check-up to see if you're suitable. Once enrolled, you would receive the study medicine, BIIB080, or a placebo (a dummy medicine), through an injection into the fluid around your spinal cord. These injections would happen either every 12 weeks (about every three months) or every 24 weeks (about every six months).

For the first 76 weeks, you wouldn't know if you're getting the active medicine or the placebo. After this initial period, if you're still eligible and wish to continue, you could enter a longer-term part of the study for another 96 weeks. During this extension, everyone would receive the active BIIB080 medicine. Most participants would need to visit the clinic about every six weeks after the initial screening period for checks and assessments. You can continue taking certain other Alzheimer's medications, but the dose must be stable before starting the study.