['alzheimer disease']
['jnj-54861911, 10 mg', 'jnj-54861911, 25 mg', 'placebo', 'jnj-54861911, 5 mg']

        Inclusion Criteria:

          -  Participants in the early Alzheimer's disease (AD) spectrum at time of enrollment
             under the parent protocol and according to its inclusion and exclusion criteria, must
             have very recently completed their treatment in a Phase 1b or Phase 2 JNJ-54861911
             clinical study (example [e.g.], 54861911ALZ2002) under the parent protocol. Enrollment
             in this study should be completed (Day 1 of double-blind [DB] treatment phase) as soon
             as possible, but within 6 weeks, following completion of their treatment period under
             the parent protocol. If not defined under the parent protocol, completion of the
             treatment period is defined as having completed all study related procedures of the
             last visit of the treatment period under the parent protocol. A screening phase of up
             to 12 weeks may be allowed following written approval of the Sponsor

          -  Participant must be willing and able to adhere to the prohibitions and restrictions
             specified in this protocol

          -  Each Participants (or their legally acceptable representative and caregiver depending
             on disease state and local requirements) must sign an informed consent form (ICF)
             indicating that he or she understands the purpose of and procedures required for the
             study and are willing to participate in the study

          -  Participants must have a reliable informant (relative, partner, or friend). The
             informant must be willing to participate as a source of information and has at least
             weekly contact with the participant (contact can be in-person, via telephone or other
             audio/visual communication). The informant must have sufficient contact such that the
             Investigator feels he/she can provide meaningful information about the participant's
             daily function. If possible, an alternate informant meeting these criteria who can
             replace the primary informant should be identified prior to randomization

        Exclusion Criteria:

          -  Any condition or situation which, in the opinion of the Investigator, may put the
             participant at significant risk, may confound the study results, or may interfere
             significantly with participant's participation in the study

          -  The use of concomitant medications known to prolong the QT/QTc interval

          -  Participant has a history of moderate or severe hepatic impairment or severe renal
             insufficiency unless completely resolved for more than a year. Participant has
             clinically significant ongoing hepatic, renal, cardiac, vascular, pulmonary,
             gastrointestinal, endocrine, hematologic, rheumatologic, psychiatric or metabolic
             conditions (e.g., requiring frequent monitoring or medication adjustments or is
             otherwise unstable)
      