2. Autism spectrum disorders: Increasing prevalence and changes in diagnostic criteria

Transcription

1 Research Signpost 37/661 (2), Fort P.O. Trivandrum Kerala, India Original Article Recent Res. Devel. Nutrition, 9(2013): ISBN: Autism spectrum disorders: Increasing prevalence and changes in diagnostic criteria Department of Human Nutrition, University of Alabama, Tuscaloosa AL, USA Abstract. In general, as compared to the published literature on prevalence, risk factors and diagnostic criteria used for autism spectrum disorders in developed countries in North America and Europe, the literature is sparse about autism in developing countries. A satisfactory diagnostic measure is currently unavailable. Therefore most of the discussion in this article deals with figures obtained from developed countries. It is assumed that in spite of cultural and other differences most of the research, particularly, diagnostic criteria used for disorders related to autism, would broadly apply to the developing countries. A Centers for Disease Control and Prevention report published in 2012 estimates that about 1 in 88 children in the U.S. has been identified with an autism spectrum disorder (ASD). This is an increase of 78% when the data from 2008 are compared with the data from This enigmatic increase in prevalence of ASD reported in 2012 coincides with the decision of the American Psychiatric Association researchers to update and significantly change the definition of autism for the first time in nearly two decades. In this brief review controversies regarding increase in estimate of prevalence, implications of changes in definition of autism spectrum disorders according to Diagnostic and Statistical Manual of Mental Disorder are discussed. Correspondence/Reprint request: Dr. Yasmin Neggers, Department of Human Nutrition, Box , Tuscaloosa AL , USA. yneggers@ches.ua.edu

2 34 Introduction Autism, also referred to as autistic spectrum disorder (ASD) and pervasive developmental disorder (PDD), is a frequent and debilitating neurological handicap in children, which is usually diagnosed in early childhood (1). Since there are no definitive biological markers of autism for a majority of cases, diagnosis depends on a range of behavioral signs. The major symptoms of autism involve problems with communication, social interaction and repetitive behaviors. Because people with autism can have very different features and symptoms, autism is thought of as a spectrum disorder (2). The complex nature of these overlapping disorders and changes in clinical definitions over time has resulted in uncertainty in monitoring the prevalence of ASDs (2). As stated earlier, in spite of major progress and comprehensive research in the medical field on chronic and acute diseases such as cardiovascular disease, diabetes, respiratory disorders, AIDS and various cancers, there is a glaring dearth of quantitative research on ASD in developing countries (3). Surprisingly, this is also true for India, one of the most populous and technologically advanced countries in the world. Satisfactory accurate data about the specific prevalence or even the criteria used to diagnose autism spectrum disorder in India is currently unavailable (4-6). Thus, it is not possible to estimate changes in prevalence of autism related disorders in the last few decades in these countries. If any condition can be categorized as culturally invariant, autism appears to be a good candidate given its biological underpinnings. However, the existing literature consists of limited ethnographic study of case reports and, suggests that the most accurate view of autism is as a biological condition that is culturally shaped in symptoms and course (7). After an intensive search on epidemiology of ASD in India, an estimated figure of more than two million people in 2009 was reported by Mukerji et al. (8) Though the frequency of ASD diagnoses has been increasing for decades, researchers cannot agree on whether the trend is a result of increased awareness, improved detection, expanding definition or an actual increase in incidence or a combination of these factors. Lack of definitive biological markers and overlapping symptoms of ASD further complicates an accurate estimation and a determination whether the steep rise in prevalence is partly an artifact of other confounding factors (8, 9). One of the most anticipated events in the health field is the publication in May 2013 of the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) (10). The group s board of trustees voted to accept the proposed changes in DSM-5 in December Some specialists

3 Autism spectrum disorders 35 and autism advocates fear that the proposal will exclude as many as 40 % of children now considered suffering from ASD (11). However, the panel that proposed changes maintains that none of the affected children will be left out and, that revisions are needed to remove confusing labels associated with ASD. The puzzle of increasing prevalence Estimates of the prevalence of the disorder in the U.S. and other countries are controversial and have been moving towards an apparent increase in rates. Prevalence estimates range from 0.07% to 1.8% (12). Experts disagree about the causes and significance of the recent increases in prevalence of ASD. Despite hundreds of studies, it is still not known why autism incidence increased rapidly during the 1990s and is still increasing in the 2000 s. The importance of accurately identifying children with autism is of utmost importance, particularly given the apparently growing prevalence, considerable family and societal cost, and recognition of importance of early diagnosis and intervention. In 1990, Congress added autism as a separate category to federal law that guarantees special education. Since then there has been an explosion of autism related treatments and services. Recently (March 30th, 2012) data from the Autism and Developmental Monitoring Network Surveillance, reported by the CDC indicated a significant increase in prevalence of ASD: - For 2008, the overall estimated prevalence of ASD among 14 ADDM sites was 11.3/1000 (1 in 88) children aged 8 years. - This estimate varied widely across all sites, from 1 in 210 in Alabama to I in 7 in Utah (Range: /1,000 children) - There were wide variations by gender and racial/ethnic groups. - Approximately 1 in 54 boys and 1 in 252 girls were identified as having ASD. The new numbers of ASD cases reported in 2012 by the CDC is the latest in a series of studies that have steadily raised the official autism estimates. These new figures mean that autism is nearly twice as common as estimated only five years ago. If these estimates for ASD (1 in 88 children) are valid and not an artifact of confounding or systematic bias due to better screening and ascertainment, then ASD affects more than 1 million children and adolescents in the United States.

4 36 A Comparison of these 2008 findings with earlier surveillance years indicates a dramatic increase in ASD prevalence over a short period: An estimated increase of 78% when the 2008 data was compared with data from 2002 (11.0/1,000 in 2008 vs. 6.4/1,000 in 2002) An estimated increase of 30% when data from 2008 was compared to 2004 (11.0/,1000 in 2008 vs. 8.0/1000 in 2004) There was an estimated increase in prevalence of 23% when the data from 2008 was compared with data from 2006 (11/1000 in 2008 vs 9/1000 in 2006) 8 year old children diagnosed with autism from 2002 to 2008* / % / % / % / % *MMWR, March 30, 2012 Vol. 61(3). Data from Autism and Developmental Disability Monitoring Network, 14 Sites, U.S., Because the ADM Network sites do not make up a nationally representative sample, these combined prevalence estimates cannot be generalized to the U.S. as a whole. Researchers have suggested that ASD onset and prevalence are similar across European and North American populations (2). In Australia, a population based study indicated that the prevalence of ASD among children born between 1983 and 1999 and diagnosed by age 8 increased by 11.9% per annum. With exception of Japan, the data are insufficient to measure ASD prevalence accurately in other cultures. Increase and discrepancies in prevalence estimates of ASD may be partly explained because most studies have focused on populations that are more likely to include children with ASD, i.e., those with histories of special needs or developmental delays. In a few studies which have included children with mainstream education, participation rate and sample size have not been adequate. The first population based autism prevalence study in Korea with 55,266 children between 7-12 years of age, reported a striking difference in the

5 Autism spectrum disorders 37 prevalence of ASD of 2.64%, as compared to previously reported estimates ranging from % (2). In this study 2/3 of ASD cases in the overall sample were drawn from mainstream school population, undiagnosed and untreated. It is unclear whether the increase in the prevalence of ASD over the past twenty years is real or an artifact of: - wider screening - broadening ASD diagnostic criteria - lower age of at diagnosis and intervention - a greater public awareness and parental advocacy Children with such diagnosis often receive state financed support services, which some experts believe may have contributed to an increase in prevalence. Dilemma of proposed changes in ASD definition A child meets the case definition if he or she displays behavior consistent with the American Psychiatric Association Diagnostic and Statistical Manual- IV, Text Revision (DSM-IV-TR) diagnostic criteria for any of the following: Autistic Disorder, Pervasive Developmental Disorder-Not otherwise Specified (PDD-NOS) including Atypical Autism or Asperger Disorder For the first time in nearly two decades, a panel of American Psychiatric Association researchers wants to rewrite the definition of autism. The group s board of trustees voted to accept on the proposals in December Field trials have begun to validate the proposed DSM-5 criteria for ASD. These trials are being conducted to evaluate new diagnostic criteria that contain several important modifications relative to DSM-IV-TR diagnoses into a single broad ASD (13-16). Among the proposals - A new autism spectrum category would be created describing symptoms that usually appear before age 3, and would encompass children with autistic disorder now referred to as severe cases, plus those with two high functioning variations:

6 38 - Autistic disorder and high functioning variations: Asperger s disorder and PDD-NOS would be eliminated, but their symptoms will be covered under a new category. - Another new category social communication disorder would include children who relate poorly to others and have trouble reading facial expressions and body language. There is concern among several groups of autism advocates and parents that the proposal will exclude as many as 40 % of children now considered autistic. However, the members of the panel that proposed changes maintain that none of the affected children will be left out and, that the revision is needed to remove confusing labels and clarify that autism can involve a range of symptoms from mild to severe. (11) It is somewhat ironic that these changes in the definition of autism are being proposed in the same year when CDC has reported a significant increase in autism cases (1 in 88 children as compared to the previous estimate of 1 in 110) (12,16). Parents and advocacy groups are concerned and have seized on the new increased rate as further evidence that autism research and services should get more attention. Conclusions Though more than a $1 billion has been spent during the past decade on ASD research, it is disappointing that the estimated prevalence of ASD has increased by 78% as compared to the 2002 estimates. Also, in the past two decades not much progress has been reported in untangling risk factors associated with ASD, or the factors which may be related to increased prevalence of ASD. However, recent identification of de novo gene mutation may account for a small but significant percentage of ASD cases. It is obvious that ASD research has a long way to go before pinpointing relevant risk factors and broadening ASD diagnostic criteria answers for increasing prevalence of ASD in the U.S. and other countries. This is especially true for developing countries like India, where research and diagnostic criteria are still in early stages of development (17). As suggested by various researchers in India, there needs to be significantly more quantitative research conducted and validated while taking ethical and sensitive cultural issues into account (18-20). References 1. Durkin SA, Mathew J, Maenner CJ, Newschaffer LL, Christopher MC, Daniels JL et al.. Advanced parental age and risk of autism spectrum disorder. Am J Epidemiol 2006, 168:

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