Preface xliii
specific molecular genetic fi ndings for rare variants of  Alzheimer’s disease and Hun-
tington’s disease have greatly advanced cl inical diagnoses, and these disorders and
others have now been separated into specific subtypes. 
•Transition in conceptualizing personality disorders. Although the benefits of a more
dimensional approach to personality disorder s have been identified in previous edi-
tions, the transition from a ca tegorical diagnostic system of individual disorders to one
based on the relative distribution of personality traits ha s not been widely accepted. In
DSM-5, the categorical personality disorder s are virtually unchan ged from the previous
edition. However, an alternative “hybrid” model has been proposed in Section III to
guide future research that separates interp ersonal functioning assessments and the ex-
pression of pathological personality traits for six specific disorders. A more dimensional
profile of personality trait expression is also proposed for a trait-specified approach. 
•Section III: new disorders and features.  A new section (Section III) has been added to
highlight disorders that requir e further study but are not sufficiently well established to
be a part of the official classification of me ntal disorders for routine clinical use. Dimen-
sional measures of symptom severity in 13 symptom domains have also been incorpo-
rated to allow for the measurement of symp tom levels of varying severity across all
diagnostic groups. Likewise, the WHO Di sability Assessment Schedule (WHODAS), a
standard method for assessing global disabilit y levels for mental disorders that is based
on the International Classification of Functi oning, Disability and Health (ICF) and is ap-
plicable in all of medicine, has been provid ed to replace the more limited Global As-
sessment of Functioning scale. It is our hope that as these measures are implemented