AD-4833/TOMM40_303 Extension Study of the Safety and Efficacy of Pioglitazone to Slow Cognitive Decline in Participants With Mild Cognitive Impairment Due to Alzheimer Disease

The drug being tested in this study is called pioglitazone. This study is designed to further evaluate the safety and effectiveness of pioglitazone on cognitive function in participants who have completed the AD-4833/TOMM40\_301. This study will look at the effectiveness of pioglitazone on cognitive decline in high-risk participants who have completed the AD-4833/TOMM40\_301 study with a diagnosis of mild cognitive impairment (MCI) due to Alzheimer's Disease (AD). The study enrolled 40 participants, but is dependent on how many decide to continue treatment in an extension phase after completing the main (301) study. Participants will continue to receive the same study medication they received during the pivotal AD-4833/TOMM40\_301 study, either: * Pioglitazone 0.8 mg tablets or * Placebo (this is a tablet that looks like the study drug but has no active ingredient). All participants will be asked to take one tablet at the same time each day throughout the study. This multi-centre trial, like its precedent pivotal trial, will be conducted worldwide. The overall time to participate in this study is minimum 2 years and a maximum of 7 years depending on when participants roll over from the 301 study. Participants will make approximately 2 visits per year to the clinic, and will be contacted by telephone 3 months after each treatment visit for a follow-up assessment, and 2 weeks after the final visit.