We thank Drs Smith and Chicoine for their interest in our work and highlighting some of the practical issues in diagnosing and managing dementia in this group. The association between trisomy 21 and early-onset Alzheimer's disease is well establishedReference Zis and Strydom¹ and dementia is now the most common cause of death in adults with Down syndrome. Despite this, there exists relatively little evidence on which to base treatment decisions.

Using a naturalistic study design, we report the effects of antidementia medication on the survival and function of 310 people with Down syndrome and dementia. Notwithstanding the limitations typical of observational studies (discussed in the paper), this work addresses a significant gap in the literature. Kaplan–Meier survival curves demonstrate significantly increased survival in the group prescribed antidementia medication. Baseline differences between those prescribed and not prescribed antidementia medication were accounted for, where possible, in a Cox regression model. This adjusted analysis showed that protection in the treated group remained, although it did not reach statistical significance because of less power and broader confidence intervals.

Functional impairment was measured using the Dementia in Learning Disabilities scale,Reference Eurlings, Evenhuis and Kengen² a standardised informant questionnaire that covers several skill domains. These data show an early protective effect of medication in mitigating cognitive decline, as is observed in individuals with Alzheimer's disease without Down syndrome.Reference Perera, Khondoker, Broadbent, Breen and Stewart³ We appreciate the concern of Drs Smith and Chicoine for quality of life. Unfortunately, there are no well-validated measures of quality of life for this group and proxy measures have been subject to limitations in people with intellectual disability. Development of such measures and their use in research studies and routine clinical care would be welcome and could focus efforts on providing optimal holistic support.

The Cochrane reviews that Drs Smith and Chicoine cite highlight the lack of evidence in this field, rather than negative results of drug intervention studies. Two of these Cochrane reviews did not include any studies at all, and the third included only one, small randomised controlled trial. The authors of these reviews, now some years old, highlight the paucity of evidence and conclude that the reviews cannot be used to guide practice.

Our cohort was recruited from specialist memory clinics for people with intellectual disability. Clinician diagnosis of dementia in such clinics is valid and reliableReference Sheehan, Sinai, Bass, Blatchford, Bohnen and Bonell⁴ and we are confident that clinicians will have adequately assessed potentially reversible causes of decline. It is important not to overlook dementia as an early diagnosis can facilitate prompt pharmacological and psychosocial treatments and effective care planning.Reference Dodd, Watchman, Janicki, Coppus, Gaertner and Fortea⁵ When dementia is diagnosed, a decision to use medication is, of course, an individual one, and should take account of the views of families and carers. Our paper provides additional evidence that could inform the decision-making process. People with Down syndrome and dementia should not be denied access to antidementia drugs.