Novel Diagnostic and Disease Stage Biomarkers in AD

1. Longitudinal study: Inclusion criteria: * MCI due to AD, or mild or moderate AD dementia according to the National Institute on Aging and Alzheimer's Association (NIA-AA) diagnostic criteria * Caregiver willing to participate as an informant * MMSE \>19 at inclusion * Brain FDG-PET/MRI or FDG/PET-CT * Able to cooperate to the investigations and give informed consent Exclusion criteria: * Other neurological or psychiatric illness that may affect neurofilament light (NfL) levels (severe neuropathy, multiple sclerosis (MS), stroke within the last 3 months, Wernicke encephalopathy) * Diagnosis of previous or current major psychiatric disorder (schizophrenia, bipolar disorder, psychosis) within last 2 years * Excessive alcohol intake or substance abuse within the last 2 years * Ophthalmological disorders that may affect pupillometry * Participating in drug trials or other intervention trials 2. Short-term study: Inclusion criteria: * Patients under investigation of a neurodegenerative disease * MMSE \>19 * Scheduled lumbar puncture/lumbar puncture performed within the last week prior to inclusion * Written consent form to the Danish Dementia Biobank * Able to cooperate to the investigations Exclusion criteria: * Other neurological or psychiatric illness that may affect NfL levels (severe neuropathy, MS, stroke within the last 3 months, Wernicke encephalopathy) * Excessive alcohol intake or substance abuse within the last 2 years * Ophthalmological disorders that may affect pupillometry * Participating in drug trials or other intervention trials 3. Cross-sectional study: Inclusion criteria - Patients: * A diagnosis of a dementia disorder * Caregiver willing to participate as an informant * MMSE \>15 at inclusion * Able to cooperate to the investigations * Able to give informed consent Exclusion criteria - Patients: * Diagnosis of previous or current major psychiatric disorder (schizophrenia, bipolar disorder, psychosis) within last 2 years * Excessive alcohol intake or substance abuse within the last 2 years * Other known brain disorder * Ophthalmological disorders that may affect pupillometry * Participating in drug trials or other intervention trials Inclusion criteria - Healthy Controls: * Able to cooperate to the investigations * Normal cognition * Age 50-90 year Exclusion criteria - Healthy Controls: * Diagnosis of previous or current major psychiatric disorder (schizophrenia, bipolar disorder, psychosis) within last 2 years * Excessive alcohol intake or substance abuse within the last 2 years * Other known brain disorder * Ophthalmological disorders that may affect pupillometry