agnosis is approximately 10 yea rs, reflecting the advanced age of the majority of individuals rather than the course of the disease; some individuals can live with the disease for as long as 20 years. Late-stage individuals are eventually mute and bedbound. Death most commonly results from aspiration in those who survive through the full course. In mild NCD due to Alzheimer's disease, impairments increase over time, and functional status gradually declinestmtil symptoms reach the threshold for the diagnosis of major NCD.
The onset of symptoms is usually in the eighth and ninth decades; early-onset forms seen in the fifth and sixth decades are often related to known causative mutations. Symptoms and pathology do not differ markedly at different onset ages. However, younger in dividuals are more likely to survive the full course of the disease, while older individuals are more likely to have numerous medical comorbidities that affect the course and management of the illness. Diagnostic complexity is higher in older adults because of the increased likelihood of comorbid medical illness and mixed pathology .