symptoms, with at least two being in the social do-
main, along with one each in the communicative do-
main and the domain of atypical activities and
interests. Individuals with at least one symptom each
in the social and communicative domains, but fewer
than six symptoms overall, are classified as PDD-NOS
as are individuals without symptoms in the domain of
atypical activities and interests. The criteria for As-
perger’s disorder uses the same social criteria as autis-
tic disorder, but requires at least one symptom in the
area of atypical activities and interests, as well as nor-
mal age of onset for language.
Prevalence of Autism
There is much controversy concerning the preva-
lence of autism. DSM-IV notes a prevalence rate of 4
to 5 cases per 10,000 in the United States, though
these data are based on diagnostic criteria from the
third edition of the DSM, criteria that have been
shown to be diagnostically more restrictive. Many in-
vestigators have suggested a prevalence rate for PDD
of around 1 in 800 cases in the United States, but no
definitive prevalence data exist for DSM-IV criteria.
It is clear, however, that more cases are being diag-
nosed. Several possible influences include earlier de-
tection, diagnosis of more mildly affected individuals,
the use of autism rather than mental retardation as
the primary diagnosis in cases of more severe mental
retardation, and the preference for this diagnosis in
geographic regions where it is associated with higher
intensity delivery of services. According to DSM-IV,
approximately 70 percent of individuals diagnosed
with autism have also been diagnosed with mild to se-
vere mental retardation.
Causes of the Disorder
The causes of autism remain incompletely under-
stood, although 40 percent to 60 percent of cases are
believed to have a genetic component traced to multi-
ple genes predisposing development of different
aspects of autism. Concordance in monozygotic
(identical) twins is around 95 percent; in dizygotic
(fraternal) twins, around 9 percent; and in siblings, 3
percent. About 15 percent to 25 percent of siblings of
individuals with autism have mild to severe language
difficulties.
Autism’s Clinical Course
Autism is usually detected in the third or fourth
year of life. Early hallmarks include a failure to begin
pointing, an apparent lack of interest in peers, a dis-
interest in playing with toys (or a disinterest in play-
ing with them the same way that others of the same
age do), and a delay in the development of speech for
communicative purposes. Children with autism have
a difficult time coordinating verbal and nonverbal
forms of communication and therefore often do not
mark acknowledgement of being spoken to with a
gaze, do not mark their own communicative speech
with eye contact directed at the listener, and do not
coordinate body gesture with gaze and vocalization in
such communicative efforts. Some children with au-
tism develop single words slowly, but then lose these
words, seldom use them, or seemingly plateau in lan-
guage development. Others develop language for the
first time around the third or fourth year of life or
after initiation of speech therapy. Early language for
a child with autism is marked by an instrumental qual-
ity with utterances mainly focused on getting needs
and wants addressed. There is typically little conver-
sational use of language.
Autism has sometimes been characterized as a
primary disorder of failing to develop a theory of
mind. Autistic children, especially in the early years,
show a fairly universal disability at assuming the per-
spective of others, engaging in planned deception, or
showing empathy or sympathy. The range of emo-
tional recognition and expression is more limited
than normal and social-emotional responses are usu-
ally severely lacking. When language does develop, it
may be characterized by use of immediate or delayed
echolalia in the form of repeating what has just been
heard (in the case of the former) or repeating some-
thing from past experience in its entirety (in the case
of the latter). Echolalia often, though not always,
serves some abbreviated communicative function re-
sulting in a characteristically stilted manner of dis-
course.
In addition to social and language deficits, autism
is often marked by odd ways of relating to the envi-
ronment, which may include adherence to unreason-
able routines, ritualized ways of carrying out everyday
activities, and a general resistance to change. Autistic
children may exhibit overly repetitive tendencies in
speech and play, and for many, novelty is generally
eschewed and exploratory activity is greatly reduced
compared to peers. There may be fixations or avoid-
ance of specific sensory stimuli, such as covering the
ears to certain kinds of sounds, visually fixating on ob-
jects with a strong vertical or horizontal axis, periph-
eral gazing at objects, sniffing objects not usually
smelled, and physical hypersensitivities—a strong
aversion to solid foods or certain types of food, or the
avoidance of certain types of clothing.Treatment for Autism
Treatment for autism is mostly based on methods
of changing maladaptive behavior and developingAUTISM 41