31.5 Autism Spectrum Disorder
1153
current DSM-5 diagnosis of autism spectrum disorder, exhibit
intellectual disability (ID).
Of interest, is that according to DSM-IV-TR, Rett syn-
drome or disorder appeared to occur exclusively in females and
is characterized by normal development for at least 6 months,
followed by stereotyped hand movements, a loss of purposeful
motions, diminishing social engagement, poor coordination,
and decreasing language use. In the formerly labeled
childhood
disintegrative disorder,
development progresses normally for
approximately 2 years, after which the child shows a loss of pre-
viously acquired skills in two or more of the following areas:
language use, social responsiveness, play, motor skills, and blad-
der or bowel control. The former
Asperger’s disorder
is charac-
terized by impairment in social relatedness and repetitive and
stereotyped patterns of behavior without a delay or marked aber-
rant in language development and usage. In Asperger’s disorder,
cognitive abilities and major adaptive skills are age appropriate,
although social communication is impaired. A survey of children
undertaken with the former autism spectrum disorders, revealed
that the average age of diagnosis was 3.1 years for children with
autistic disorder, 3.9 years for children diagnosed with pervasive
developmental disorder not otherwise specified, and 7.2 years for
those youth with Asperger’s disorder. Children with autism spec-
trum disorder who exhibited severe language deficits received
an autism spectrum disorder diagnosis, on average, a year ear-
lier than children without impairment in language. Children
with autism spectrum disorder who exhibited repetitive behav-
iors such as hand-flapping, toe-walking, and odd play were also
identified with autism spectrum disorder disorders at a younger
age than those who did not exhibit such behaviors. The current
DSM-5 autism spectrum disorder criteria provide specifiers for
severity of the main domains of impairment and also specifiers
for the presence or absence of language impairment and intel-
lectual impairment.
History of Autistic Disorder
“Early infantile autism” was described by Leo Kanner in 1943;
however, even as early as 1867, the psychiatrist Henry Maudsley had
observed a group of very young children with severe mental disorders
characterized by marked deviation, delay, and distortion in development.
In that era, most serious developmental disturbance in young children
was believed to fall within the category of psychoses. Kanner’s clas-
sic paper “Autistic Disturbances of Affective Contact,” coined the term
infantile autism
and provided a clear, comprehensive account of the early
childhood syndrome. Kanner described children who exhibited extreme
“autistic aloneness”; failure to assume an anticipatory posture; delayed
or deviant language development with echolalia and often with pro-
nominal reversal (using you for I); monotonous repetitions of noises or
verbal utterances; excellent rote memory; limited range of spontaneous
activities, stereotypies, and mannerisms; and anxiously obsessive desire
for the maintenance of sameness and dread of change. Socially, Kan-
ner’s sample was described as having poor eye contact; awkward rela-
tionships; and a preference for pictures and inanimate objects. Kanner
suspected that the syndrome was more frequent than it seemed, and sug-
gested that some children with infantile autism may have been misclassi-
fied as “mentally retarded” or schizophrenic. Before 1980, children with
symptoms of autism spectrum disorder were generally diagnosed with
childhood schizophrenia. Over time, it became evident that autism spec-
trum disorder and schizophrenia were two distinct psychiatric entities. In
some cases, however, a child with autism spectrum disorder may develop
comorbid schizophrenic disorder later in childhood.
Epidemiology
Prevalence
Autism spectrum disorders have been increasingly diagnosed
over the last two decades, with the current prevalence estimated
at approximately 1 percent in the United States. Autistic disor-
der, based on DSM-IV-TR criteria, is believed to occur at a rate
of about 8 cases per 10,000 children (0.08 percent). By defini-
tion, the onset of autism spectrum disorder is in the early devel-
opmental period; however, some cases are not recognized until
the child is much older. Because of this delay between onset
and diagnosis, the prevalence rates increase with age in young
children.
Sex Distribution
Autism spectrum disorder is diagnosed four times more often
in boys than in girls. In clinical samples, girls with autism spec-
trum disorder more often exhibit intellectual disability than
boys. One potential explanation for this is that girls with autism
spectrum disorder without intellectual disability may be less
likely to be identified, referred clinically, and diagnosed.
Etiology and Pathogenesis
Genetic Factors
Family and twin studies suggest that autism spectrum disor-
der has a significant heritable contribution; however, it does
not appear to be fully penetrant. Although up to 15 percent
of cases of autism spectrum disorder appear to be associated
with a known genetic mutation, in most cases, its expression is
dependent on multiple genes. Family studies have demonstrated
increased rates of autism spectrum disorder in siblings of an
index child, as high as 50 percent in some families with two
or more children with autism spectrum disorder. Siblings of a
child with autism spectrum disorder are also at increased risk
for a variety of developmental impairments in communication
and social skills, even when they do not meet criteria for autism
spectrum disorder.
The concordance rate of autistic disorder in two large twin
studies was 36 percent in monozygotic pairs versus 0 percent
in dizygotic pairs in one study and about 96 percent in mono-
zygotic pairs versus about 27 percent in dizygotic pairs in the
second study. High rates of cognitive impairments, in the nonau-
tistic twin in monozygotic twins with perinatal complications,
suggest that contributions of perinatal environmental factors
interact with genetic vulnerability differentially in autism spec-
trum disorder.
The heterogeneity in expression of symptoms in families
with autism spectrum disorder suggests that there are multiple
patterns of genetic transmission. Studies indicate that both an
increase and decrease in certain genetic patterns may be risk
factors for autism spectrum disorder. In addition to specific
genetic factors, gender plays a strong role in the expression of
autism spectrum disorder. Genetic studies have identified two
biological systems that are influenced in autism spectrum disor-
der: the consistent finding of elevated platelet serotonin (5-HT),
and the mTOR, that is, mammalian target of rapamycin–linked
synaptic plasticity mechanisms, which appear to be disrupted
