Epidemiology
ASDs include 3 neurodevelopmental disorders – the autistic disorder,
Asperger syndrome, and pervasive developmental disorder-not otherwise specified
(PDD-NOS ). The latest estimated prevalence of ASDs is approximately 6 per 1000,
or around 1 in 150 children.[1] Most reports indicate that the perceived rise in
the rates of ASDs is due to better diagnostic procedures and an increased
awareness leading parents to bring their children for evaluation.[1] The notable
decrease in percentage of children diagnosed with ASDs with accompanying mental
retardation supports the notion that high functioning children are now more
frequently included in the epidemiological reports on ASDs.[1] Studies
consistently find that ASDs occur more frequently in boys, with the
male-to-female ratios ranging from 2:1 to 6.5:1.[1]
Causes
While the exact mechanisms that cause ASDs are not fully understood,
existing evidence suggests that complex interacting genetic factors are involved
in these highly heritable disorders, with environmental factors also playing a
role. Exposure to toxins affecting the central nervous system in early
gestational life has been linked to increased risk for ASDs. Researchers are
also exploring epigenetic causes of ASDs, meaning heritable changes in gene
expression as opposed to altered DNA sequence.
In 5%–10% of cases, ASDs are associated with an identifiable medical
disorder with a known inheritance pattern, such as fragile X syndrome, tuberous
sclerosis, Angelman syndrome and Rett syndrome. The majority of cases are
idiopathic, and as a result many parents blame themselves and need reassurance
that they did not cause the disorder through faulty parenting, as was thought 50
years ago.
Many parents continue to fear that vaccinations cause autism, despite
several reports by the Immunization Safety Review Committee, which, after
reviewing epidemiological data, stated that there was not sufficient evidence to
support a causal relationship between autism and the MMR vaccine, nor any
vaccine containing the mercury-containing compound thimerosal.[2] While it is
true that a sufficient dose of mercury is neurotoxic, the clinical
manifestations of mercury toxicity and autism are quite different.[3] It is
important to note that the timing of the onset of symptoms after a period of
normal development does not necessarily imply that an environmental exposure is
the cause. Regardless of vaccinations, children with ASDs often present with
typical development followed by a period of regression in the second year of
life.[1] Despite the lack of evidence that children who receive vaccinations
have an increased incidence of autism, many parents remain skeptical and may
benefit from discussion with their pediatrician.
Areas of impairment
Three areas of impairment are found in children with ASDs. First and
primary is impaired social interaction, which may beextreme and include lack of
eye contact, not responding to one's name, or preferring to play alone. More
subtle characteristics include a lack of sharing attentional and emotional
states. For example, a child may smile in response to something exciting, such
as a pop-up toy or bubbles, but not turn to look at his parents to share that
enjoyment. Similarly, a child with an ASD may not point to things of interest,
and if he does point, he may not turn back to ensure his parent is also looking.
Other symptoms may include an inability to form friendships or a lack of
nonverbal behaviors, including gestures or facial expressions that regulate
social interaction.
Second, impairments in communication are found in children with ASDs. In
children with PDD-NOS and autistic disorder, the primary symptom is a delay in,
or total lack of, the development of spoken language. Persons with Asperger
syndrome do not have a general delay in language or cognitive development, as
noted by acquisition of first words by age 2 years and phrases by age 3 years.
Nevertheless, children with Asperger syndrome often have some communication
difficulties, especially in sustaining conversations, and they are often rigid
by only pursuing conversations on certain areas of interest. Other speech
abnormalities associated with ASDs include echolalia (ie, repeating final
phrases just heard by another person), lack of prosody (ie, monotonic or odd
intonation), and stereotypic language (ie, repeating scripts from TV programs).
In addition, children with ASDs typically have a delay in pretend/symbolic play,
which is a precursor to the development of language, as language is a collection
of symbols to make communication possible.
The third area of impairment in ASDs is restricted or repetitive
behaviors. In its extreme form, typical manifestations include staring at
spinning toys and flapping hands, having an odd interest in objects such as
shiny objects, street drains, or ceiling fans. Some children may have a typical
interest, such as trains or dinosaurs, but the interest is very intense and the
child many only play with toys of that kind, or he may develop an oddly advanced
knowledge in his area of interest. Children may be preoccupied by parts of
objects and toys rather than understanding their intended use. For example, the
child may spin the wheels of a car or roll it back and forth in front of his
eyes while lying down, instead of rolling the car and pretending it is going
somewhere. Children with autism often adhere to inflexible routines and have
difficulty with changes in routine and/or transitions from one activity to the
other.
There is great variability in the presentation of children with ASDs and
the distinction between the autistic disorder, Asperger syndrome, and PDD-NOS
depends on the distribution and number of symptoms present. A child certainly
does not have to have all the symptoms to qualify for a diagnosis of an ASD. For
example, clinicians should not rule out a suspicion of ASDs if the child uses
eye contact, since this is only 1 symptom out of many that a child might
manifest.
Red flags
ASDs are typically diagnosed by taking a comprehensive developmental
history, observation of a child with his parent, and an interactive play session
with a diagnostician. To identify as early as possible children who should be
referred immediately for diagnostic evaluation, pediatricians need to watch for
the following ASD red flags suggested by the American Academy of Neurology and the Child
Neurology Society[1]:
- No babbling, pointing, gesturing by 12 months
- No single words by 16 months
- No spontaneous 2-word combinations by 24 months
- Loss of language or social skills at any age
Risk factors
An important risk factor is an older sibling with an ASD. This calls for
careful observation and ongoing monitoring by the pediatrician. The rates of
having a second child with an ASD increase 10-fold to 2%–8%.[4] Other risk
factors to consider during every well child visit include parental concerns,
other caregiver concerns and the pediatrician's own concerns based on
observation of the child's development in social interaction, communication and
behavior.
If a risk factor is noted, the AAP recommends the use of an ASD-specific
screening tool. For children younger than 18 months, a standardized screening
tool is available for assessing social and communication deficits typical in
ASDs. (See Table 1 for age-specific screening tools that can be downloaded at no
cost.) Clinicians may refer to the AAP report for an extensive list of ASD
screening tools.[1] Two or more risk factors or positive screening results
warrant a simultaneous referral for ASD evaluation, early intervention services
and an audiologic evaluation.
Universal screening
The AAP recommends for all children to be screened with a standardized
ASD-specific screening tool at the 18-month preventive care visit, even if
patients do not exhibit any autistic signs. Since developmental regression is a
common feature of ASDs, a second screening at the 24-month visit is advised for
all children.
Treatment options
While there is no cure for autism, the earlier treatment is initiated,
the more promising the outcomes. Positive outcomes include, but are not limited
to, increases in IQ points and language development, and improvements in social
behaviors, such as eye contact, reciprocal interaction and cooperative play.
Most empirically-based treatments are behavioral interventions and are offered
through the state early intervention programs and public schools. These include
speech therapy, occupational therapy, and structured preschool programs. In
addition, private therapists, typically board certified behavioral analysts
(BCBAs), provide specialty behavioral treatment, including applied behavior
analysis and verbal behavior analysis. Medication treatment is used in some
cases to allay symptoms of extreme hyperactivity and/or aggression. An overall
rule of thumb is that approximately 20–25 hours per week of intervention,
including preschool and therapies, is recommended.
Summary
Clinical manifestations of ASDs are highly variable, making diagnosis
extremely challenging. Familiarity with the characteristic areas of impairment
seen in children with ASDs, risk factors, red flags, and ASD-specific screening
tools should help pediatricians identify children who need diagnostic evaluation
and intervention services. Screening all children for ASDs at the ages
recommended by the AAP should also promote earlier diagnosis and treatment,
facilitating more positive outcomes.
References
[1.] Johnson CP, Myers SM, and the Council on Children with Disabilities,
American
Academy of Pediatrics.
Identification and evaluation of children with autism spectrum disorders.
Pediatrics 2007 Nov;120(5):1183-1215.
[2.] Institute of Medicine, Immunization Safety Review
Committee. Immunization Safety Review: Vaccines and Autism. Washington, DC: National Academies Press; 2004.
[3.] Nelson KB, Bauman ML. Thimerosal and autism? Pediatrics
2003;111:674-679.
[4.] Muhle R, et al. The genetics of autism. Pediatrics 2004;113(5):
e472-e486. Available at:
http://pediatrics.aappublications.org/cgi/content/full/113/5/e472. Accessed
October 23, 2008. |  |
