Major and Mild Neurocognitive Disorders 609
the pattern of onset of cognitive deficits and associated features helps to distinguish among
them. 
NCDs with onset in childhood and adolescence may have broad repercussions for so-
cial and intellectual development, and in th is setting intellectual disability (intellectual
developmental disorder) and/or other neurod evelopmental disorders may also be diag-
nosed to capture the full diagnostic picture and ensure the provision of a broad range of
services. In older individuals, NCDs often occu r in the setting of medical illnesses, frailty,
and sensory loss, which complicate the clin ical picture for diagnosis and treatment. 
When cognitive loss occurs in youth to midlife, individuals and families are likely to
seek care. NCDs are typically easiest to identify at younger ages, although in some settings
malingering or other factitious disorders may be a concern. Very late in life, cognitive
symptoms may not cause concern or may go unnoticed. In late life, mild NCD must also be
distinguished from the more mo dest deficits associated with “normal aging,” although a
substantial fraction of what has been ascribe d to normal aging likely represents prodromal
phases of various NCDs. In addition, it beco mes harder to recognize mild NCD with age
because of the increasing prevalence of me dical illness and sensory deficits. It becomes
harder to differentiate among subtypes with ag e because there are multiple potential sources
of neurocognitive decline.
Risk and Prognostic Factors 
Risk factors vary not only by etiological subtype but also by age at onset within etiological
subtypes. Some subtypes are distributed thro ughout the lifespan, whereas others occur
exclusively or primarily in late  life. Even within the NCDs of aging, the relative prevalence