DALLAS: Individuals with Down syndrome who survive into adulthood face the additional challenge of early-onset dementia, in which toxic amyloid plaques build up in the brain. The condition is strikingly similar to Alzheimer’s disease, and as new work led by researchers shows dementia in Down syndrome involves defects in a regulatory enzyme known as γ-secretase activating protein (GSAP), which also happens to malfunction in Alzheimer’s disease.