APP and Alzheimer disease: In addition to AD, signs of ageing-related reduction in tissue regenerative capacity (such as alopecia, xerosis, delayed wound healing, chronic periodontitis, osteoporosis and immunosenescence) are often seen in DS earlier than in age-matched euploid individuals.4, 5, 6, 7 While increased incidence and earlier onset of AD in DS is clearly caused by the triplication of the chromosome 21 (chr21) gene for amyloid precursor protein (APP),8,9 the explanations for all other ageing-related phenomena are less well understood.10