Memantine and Down's Syndrome

Inclusion criteria will be:

1. Participants with learning disabilities due to Down's syndrome (DS) confirmed by karyotype. A clinical diagnosis (provided by the participant's general practitioner or hospital specialist) will be accepted if karyotype is not known and participant does not agree to have it tested

2. Ages 40 years and over or any age if a diagnosis of dementia is established

3. In participants with dementia, the diagnosis will be consistent with the 10th version of the International Classification of Diseases (ICD-10) (World Health Organization [WHO], 1992) diagnostic criteria

4. Level of speech and comprehension of verbal commands are sufficient to understand and to answer simple requests

5. Resident in care facility or community living with a carer who is willing to accept responsibility for supervising the treatment and will provide input to efficacy parameters in accordance with protocol requirements

6. Not receiving treatment with memantine currently or in past 4 weeks and responsible clinician not considering treatment with memantine

7. Participant willing to take part in study; and carer, with capacity, willing to assent to study and agrees that participant can take part if participant is also willing

Exclusion criteria will be:

1. Participants known to have sensitivity to memantine

2. Severe, unstable or uncontrolled medical or psychiatric conditions apparent from history, physical examination or investigations

3. A current diagnosis of primary neurodegenerative disorder other than dementia such as Huntington's disease, etc.

4. Uncontrolled epilepsy

5. Presence of challenging behaviour likely to preclude the participation during testing

6. Presence of severe motor or sensory impairment (severe deafness or blindness) that renders the participant as untestable with the battery of tests used in the study

7. Current evidence of delirium

8. Severe renal impairment

9. Low probability of treatment compliance

10. Previous evidence of lack of efficacy or tolerability to memantine

11. Taking any of the following substances: