Autism Rates in the USA: Where did the 1 in 150 number come from?

As I read Autism related blogs, discussion forums, and news articles, I see many people using the number 1 in 150 to refer to the current rates of autism. Yet, few know or understand where this number comes from and how it was obtained. I hope this brief review can provide some clarity on this issue:

The autism rate of 1 in 150 was published by the US Center for Disease Control in 2007 as part of a weekly disease morbidity and mortality surveillance report. The 1 in 150 rate was obtained from a population-based study of 8 year old children conducted in 2002. Specifically, teams in 15 US States reviewed health and educational records of children born in 1994. Trained clinicians classified them as having an autism spectrum disorder if:

1) had a documented previous classification of an ASD (i.e., the child had either an uncontradicted record of an autistic disorder or ASD diagnosis provided by a qualified examiner or documentation of qualification for special education services during 1994--2002 under an autism eligibility category)
or
2) did not have a documented ASD classification but had an evaluation record from an educational or clinical source indicating unusual social behaviors consistent with an ASD.

However, the clinical team conducted an additional detailed analysis of the records to ensure that the accepted DSM-IV criteria for autism and ASD was met prior to classifying each child. Thus, classification was not only based on prior records, but also included a secondary analysis by a clinical team that utilized structured procedures to maximize the validity and reliability of their diagnostic process.

The results:
Overall, the teams reported a rate of 6.6 per 1,000 children as meeting the diagnostic criteria for ASD (1 in 151). Rates by State varied significantly, but this was affected by differences in the way rates were obtained. Some States were able to determine rates based on health records AND educational records, while others could not get access to educational records. As expected, States that had access to educational records had higher prevalence rates than those that only examined health records. On average, States with access to educational and health records reported an autism prevalence rate of 7.2 per 1,000 (1 in 139), while those with only access to health record reported a rate of 5.1 per 1,000 (1 in 196). The male to female ratio significantly varied by State and ranged from 3.4 to 1 in Maryland to 6.5 to 1 in Utah.

Things to keep in mind:
- This report was based ONLY on children born in 1994. Thus it is possible that the rates could not apply to other cohorts.
- The differences in prevalence rates between States with and without access to educational records could suggest that 1) the overall rate is an underestimate because some sites only had access to health records, or 2) that the overall rate is an overestimate because some sites included cases ascertained from educational records which may be less reliable than health records.
- This rate of 1 in 150 does not refer to new cases of autism, or total cases in the population. It only speaks to cases among 8 year old children in 2002.

Autism and Cholesterol: A possible link?

Low levels of cholesterol associated with autism-like symptoms in Smith-Lemli-Opitz Syndrome.

A review of: Aneja, A., Tierney, E. (2008). Autism: The role of cholesterol in treatment. International Review of Psychiatry, 20(2), 165-170. DOI: 10.1080/09540260801889062

The Smith-Lemli-Opitz Syndrome (SLOS) is a genetic disorder characterized by alterations in the processing of cholesterol. Specifically, people with this disorder do not produce enough cholesterol resulting in a variety of morphological, physiological, and behavioral symptoms. Of interest to autism researchers is that people with SLOS have many of the same symptoms that characterize autism spectrum disorders, including language impairments and stereotyped behaviors. How is cholesterol related to ASDs within and outside the SLOS syndrome? In this article, Aneka and Tierney (2008) present a succinct summary and conceptualization of the possible role of cholesterol in the phenomenology of Autism. The authors reviewed the physiological mechanisms by which low levels of cholesterol may play a role in the behavioral phenotype found in kids with SLOS. The following mechanisms were discussed:
1. Cholesterol is necessary for normal embryonic and fetal development.
2. Cholesterol is a precursor of neuroactive steroids (possibly affecting anxiety)
3. Cholesterol is required for the growth of myelin membranes (affecting brain maturation).
4. Cholesterol can be a modulator in oxytocin receptor functioning (Oxytocin plays an important role in social behaviors).
5.Cholesterol is a modulator of the ligand binding activity and G-protein coupling of the serotonin1A (5-HT1A) receptor (affecting serotonin neuron development).

An examination of these factors is beyond the scope of this review, but they represent a sensible theory regarding the possible mechanisms by which low levels of cholesterol may lead to many of the behavioral symptoms present in autism. The authors then discussed the implication of these findings for assessment and possible treatment interventions. First, most comprehensive evaluations of autism may include genetic and laboratory testing, including testing for fragile X, heavy metals, etc. The authors stated that biochemical testing can be utilized to assess for low level of cholesterol (actually low levels relative to another compound - 7DHC). In my experience, requesting this test within a neuropsychological evaluation is not common. Actually I don’t remember ever conducting an evaluation of someone who had been recommended this test by anyone (neurologist, pediatricians, psychologist, etc). Finally, the authors reviewed previous studies that have examined the effectiveness of cholesterol supplementation in children with SLOS. Previous studies have found that children with SLOS that receive cholesterol supplementation show a reduction of autistic behaviors, irritability, attention problems, and improved affect.

Should cholesterol testing become a part of the standard assessment procedures of children with Autism?

Autism epidemic and symptom substitution

Study provides evidence for the symptom substitution theory explaining the dramatic increases in autism during the last 20 years.

A review of: Bishop , D., Whitehouse , A., Watt , H., Line , E. (2008). Autism and diagnostic substitution: evidence from a study of adults with a history of developmental language disorder.. Developmental Medicine and Child Neurology, 50, 1-5.

One theory that has been proposed as a possible explanation of the dramatic increase in autism diagnoses during the 1990’s and 2000s is the Diagnostic Substitution phenomena. The basic premise of this position is that increases in autism diagnoses are not due to a true increase in the number of ‘cases’ of autism, but instead to a change in diagnostic practices so that individuals who are now diagnosed with autism would have been diagnosed with a different condition 20 or 30 years ago.

What are the basic assumptions about this theory that can be tested? First, an increase in diagnoses of autism should be accompanied by an equally dramatic decrease in diagnoses of other related disorders that are believed to drive the substitution. Sullivan at Gray Matter – White Matter provides a great example of this phenomenon by looking at the rates of autism and mental retardation in Alabama. Another way to test this theory would be to examine retrospectively the clinical presentation of adults who have been diagnosed with a non-autism disorder, and determine if the clinical presentation of these individuals during childhood would have led to a diagnosis of Autism today. That is, would children with the same presentation receive a diagnosis of autism today?

In this study, the authors examined 38 adults (age 15 to 31) who had received a diagnosis of language disorder during childhood but not a diagnosis of Autism. The authors were mostly interested in a particular type of language disorder diagnosis called pragmatic language impairment (PLI), since this disorder has many similarities with autism. The authors conducted full ADOS and ADI evaluations of these individuals. They found that 55% of the participants with PLI met the criteria of autism as indicated by the ADOS or the ADI, and 40% met the criteria of autism as indicated by both, the ADOS and the ADI.

These findings are consistent with the diagnostic substitution theory. The implication is that a significant percentage of people who were diagnosed with PLI in the past would now receive a diagnosis of autism instead. Likely this substitution is not sufficient to explain, in its entirety, the dramatic increase in autism diagnoses; but it is reasonable to conclude that such substitution could partially explain such increase. In addition, the PLI substitution is just one of several proposed substitutions (see for example MR as described here). Finally, it could be argued that these individuals received the correct diagnosis of PLI as children and developed autism symptoms as adults. Although this is a plausible explanation, it is not consistent with what we know of the developmental progression of autism symptoms.

Hospitalization of Children with Autism: Predictors and Frequency

Aggressive behaviors increase risk for hospitalization by more than 400%; more than any other variable.

A review of: Mandell, D.S. (2007). Psychiatric Hospitalization Among Children with Autism Spectrum Disorders. Journal of Autism and Developmental Disorders DOI: 10.1007/s10803-007-0481-2

In this large-scale study the authors examined the frequency and predictors of psychiatric hospitalization in children with autism spectrum disorders. The sample included 760 children and young adults with a diagnosis of autism, Asperger’s or PDD-NOS and their parents (age range of the children 5 to 21) living in Pennsylvania. 10.8% of the sample had a history of psychiatric hospitalization. A number of external factors were more common in children and young adults with ASDs. Those with a history of hospitalization were more likely to be: older, African-American, adopted, living in a single parent household, and have parents making less than 40,000 per year and without a college degree. In addition to these external factors, those with a history of hospitalization were also more likely to: have a diagnosis of Autism or Asperger’s (as opposed to PDD-NOS), display self-injurious behaviors, be aggressive towards others, display less stereotypies, and have more co-morbid diagnoses.

When examining the predictors of hospitalization a slightly different picture was noted. Each year of age was associated with a decrease in hospitalization risk (OR=.81). This sounds like it contradicts the finding reported above - that those with a history of hospitalization are more likely to be older. However, these are two different questions. At the group level, older people, likely simply by virtue of living longer, are more likely to have a history of hospitalization. However, at the individual level, the risk of hospitalization decreases with age, so that it becomes less likely in each subsequent year. Aggressive behavior towards others was the stronger predictor of hospitalization increasing the odds more than 400% (OR= 4.83). This was followed by having a co-morbid diagnosis of depression (OR = 2.48) or obsessive compulsive disorder (OR=2.35), and displaying self-injurious behaviors (OR=2.14). One parental variable were also identified. Living in a single parent home more than double the odds of being hospitalized (OR=2.54).

One of the most interesting issues addressed by this research is that it seems that there are two factors related to risk of hospitalization: factors that are directly reflective of the severity of the disorder (aggression, self-injurious behaviors, etc) and social-familial factors that are possibly unrelated to the disorder (SES, being a single parents, etc). It is possible that the effectiveness and utility of hospitalization may depend upon the underlying reasons as to why a child may be hospitalized. In addition, this data suggest that interventions targeted to reducing the rate of hospitalization among children with ASD should focus on: early treatment of aggressive and self-injurious behaviors, and providing better services and resources to families at risk for seeking hospitalization for their children.