Please find attached studies and references, James.
Head et aL (2007). Possible Compensatory Events in Adult Down Syndrome Brain Prior to the Development of Alzheimer Disease Neuropathology: Targets for Non pharmacological Interventions. Journal of Alzheimer's Disease, 11(1), 61-76, DOI: 10.3233/JAD-2007-11110
Kendall, R. & Jablensky,A.(2003). Distinguishing Between the Validity and Utility of Psychiatric Diagnoses. Am J Psychiatry 2003; 160:4–12. https://pdfs.semanticscholar.org/34d5/f3ff43453b57f338b149230e3b30d4ed3f1b.pdf
Karen Dodd, (2010) "Psychological and other non‐pharmacological interventions in services for people with learning disabilities and dementia", Advances in Mental Health and Learning Disabilities, Vol. 4 Issue: 1, pp.28-36, https://doi.org/10.5042/amhld.2010.0056
Hagberg B, Aicardi J, Dias K, Ramos O. A progressive syndrome of autism, dementia, ataxia, and loss of purposeful hand use in girls: Rett’s syndrome: report of 35 cases. Ann Neurol. 1983;14(4):471–9.
Jellinger K, Armstrong D, Zoghbi HY, Percy AK. Neuropathology of Rett syndrome. Acta Neuropathol. 1988;76(2):142–58.
Rumble et al (1989). Amyloid A4 Protein and Its Precursor in Down's Syndrome and Alzheimer's Disease. The New England Journal of Medicine. 320:1446-1452. DOI: 10.1056/NEJM198906013202203
Rodakowski, et al (2015). Non-pharmacological Interventions for Adults with Mild Cognitive Impairment and Early Stage Dementia: An Updated Scoping Review. Mol Aspects Med. 0,38–53.
Rivas-Vazquez et al (2004). Mild cognitive impairment: new neuropsychological and pharmacological target. Archives of Clinical Neuropsychology, 19(1), 11-27. https://ac.els-cdn.com/S0887617702001671/1-s2.0-S0887617702001671-main.pdf?_tid=f2a44ed4-c604-11e7-b5c7-00000aab0f26&acdnat=1510311201_dcf3f73c724ef95f655f7c1ff52a88b6
Hashimoto et al (2004). Executive dysfunction can explain word-list learning disability in very mild Alzheimer's disease: The Tajiri Project. Psychiatry and Clinical Neurosciences (2004), 58-60. http://onlinelibrary.wiley.com/doi/10.1111/j.1440-1819.2004.01193.x/epdf
Lifshitz, H. & Klein, P.S. (2011).Mediation between Staff and Elderly Persons with Intellectual Disability with Alzheimer Disease as a Means of Enhancing Their Daily Functioning. Education and Training in Autism and Developmental Disabilities, 46(1), 106 –115. http://daddcec.org/Portals/0/CEC/Autism_Disabilities/Research/Publications/Education_Training_Development_Disabilities/2011v46_Journals/ETADD_201103v46n1p106-115_Mediation_between_Staff_and_Elderly.pdf