In recent years, the life expectancy of individuals with Down Syndrome (DS) has increased significantly thanks to the advancements in healthcare and treatments, giving rise to an older population of people with DS. However, this demographic shift has brought about new concerns: as individuals with DS age, they face a higher incidence of early-onset Alzheimers Disease (EOAD) (i.e. the development of AD before the age of 65). Research has revealed an accelerated progression of symptoms, from onset of dementia to death, in DS patients. Thus, it is essential to identify the factors (both genetic and environmental) that underlie the development of different stages of AD-DS. Concomitantly, there is a pressing need to initiate intervention trials that could slow down or prevent the rapid advancement of AD-DS. This paper underscores the growing importance of addressing AD-DS in an ageing DS population. By elucidating genetic and environmental factors, clinical features, diagnostic challenges, roles of genes in the development of AD-DS, and potential future research directions, the article aims to contribute to a deeper understanding of dementia of the Alzheimer Type (DAT) and facilitate the development of effective treatments that could improve the lives of DS individuals affected by DAT.