by Michael D. Anestis, M.S.
Last week, I wrote an article discussing some of the proposed changes to the autism spectrum in the upcoming DSM-V. The article was based upon a review in the New York Times (NYT) - an unusual inspiration for a PBB article, but one that seemed worthwhile given the quality of the NYT piece. Of the proposed changes, the most monumental and controversial is the potential for shifting the diagnoses of Asperger's syndrome and pervasive developmental disorder not otherwise specified (PDD-NOS) into a single autism spectrum disorder diagnosis in response to evidence indicating that there are no qualitative differences between these disorders and autism proper. The comments readers left on the article were fascinating and I was already considering a follow-up when, this morning, I came across an editorial - again in the NYT - written by Simon Baron-Cohen of the Autism Research Center at Cambridge University. Dr.Baron-Cohen weighed in on this same issue and detailed why he believes that this decision would be premature and potentially harmful and I wholeheartedly urge you to read his well-written commentary (link).
I wanted to touch on this topic again today for a number of reasons. First, I wanted to provide a resource written by an expert on the field that provides a more cautious opinion of the matter than was presented in the original NYT piece and the PBB article that I wrote. Doing so provides more balance in the evidence. Additionally, I wanted to respond to a couple of points written by Dr. Baron-Cohen with which I do not entirely agree (or disagree). Before doing any of this, however, let me provide you with a brief overview of the author. Dr.Baron Cohen is an extremely prolific researcher on this topic. In fact, a quick PsycInfo search revealed 210 publications in peer reviewed journals. To put it mildly, that is incredibly impressive. The sheer number of publications, however, does not do justice to the quality. Recent published works on which he has contributed have provided impressive insight into basic physiological differences that define the autism spectrum. For instance, one study demonstrated that individuals with autism spectrum conditions (ASC) exhibited enhanced visual acuity relative to individuals without ACS's and that this enhanced acuity lies in the region of birds of prey (Ashwin, Ashwin, Rhydderch, Howells, & Baron-Cohen, 2009). This, of course, lends empirical evidence to the general belief in a hypersensitivity to sensory stimuli in ASC. In another study, Minio-Paluello, Baron-Cohen, Avenanti, Walsh, and Aglioti (2009) found that individuals with Asperger's syndrome demonstrated a paucity in empathic responses to the observation of painful stimuli in other people as measured through single-pulse transcranial magnetic stimulation. His work is thus providing a strong biological foundation for our understanding of the autism spectrum.
All this being said, in his NYT editorial this morning, Dr. Baron-Cohen opined that the proposed changes related to the Asperger's diagnosis are premature for a number of reasons. First, because the DSM system is not based upon taxometric analyses, it is unclear whether our diagnostic entities represent naturally occurring, distinct groups and, as such, reshuffling the deck in a substantial way might not represent valid scientific progress. Secondly, he wonders whether this shift would cause distress and confusion for individuals who have received the Asperger's diagnosis and potentially negatively impact their ability to obtain services. Third, he claims that the scientific world has not had enough time to test for biological differences between Asperger's and other ASC's - Asperger's syndrome was not added until DSM-IV, after all - and, as such, removal would prevent a clear understanding of the phenomenon.
Point 1: Taxometrics
Put briefly, taxometrics refers to the process of analyzing whether an entity represents a naturally occurring group (a taxon) or a dimensional construct. A couple significant issues in mental health research are the degree to which we can provide a single comprehensive definition of mental illness and the degree to which the diagnoses listed within the DSM (or ICD) represent naturally occurring phenomena as opposed to man-made collections of symptoms of questionable validity. Taxometric analyses can, at least to an extent, provide answers to those questions (for a reader friendly review of this topic, I recommend Joiner & Schmidt, 2002 and Schmidt, Joiner, & Kotov, 2004. See our References page for the full citations).
In an early lecture during my first year in graduate school, Brad Schmidt explained the concept of taxometrics to me and my classmates in a distinctive manner that has stayed with me ever since: "There are gophers and there are chipmunks but there are no gophmunks." In other words, gophers and chipmunks both represent taxa - naturally occurring qualitatively distinct groups and do not lie upon a single gopher-chipmunk continuum.
Dr.Baron-Cohen is absolutely correct in arguing that the DSM is not based upon taxometrics. I wanted to respond to the comment not to argue, but rather to call attention to some of the work that is going on out there on this topic because, in reality, a number of researchers are, in fact, making serious attempts to examine the degree to which diagnostic categories (or features within diagnoses) represent a taxon versus a continuum. For instance, research supports the idea that schizotypy is taxonic, (e.g., Lenzenwager & Korfine, 1992). Additionally, whereas research indicates that antisocial behavior and personality appear to be taxonic (e.g., Skilling, Quinsey, & Craig, 2001), psychopathy falls along a continuum (e.g., Marcus, John, & Edens, 2004). Some researchers have demonstrated that depression is a dimensional construct (e.g., Ruscio & Ruscio, 2000); however, others have found support for the notion that depressive subtypes (e.g., melancholic depression) are taxonic (e.g., Haslan & Beck, 1994). Some research supports the possibility of eating disorder taxa (Gleaves, Lowe, Snow, Green, & Murphy-Ebernez, 2002; Williamson, et al., 2000). Within anxiety, worry and PTSD have been shown to be non-taxonic (Ruscio, Borkovec, & Ruscio, 2001; Ruscio, Ruscio, & Keane, 2002), whereas general anxiety and anxiety sensitivity have demonstrated evidence of being taxonic (Kotov, Schmidt, Lerew, Joiner, & Ialongo, 2005; Schmidt, Kotov, Lerew, Joiner, & Ialongo, 2005 - and thanks to Jill Holm-Denoma and Tony Richey, whose earlier work guided me to these articles). The point in all of this is that we are making progress on this issue and that changes made in the DSM-V with respect to dimensional diagnoses will not be based purely upon committee opinions, but also a growing mountain of empirical research on the validity of such distinctions.
Point 2: The impact of the change on people with the diagnosis
Obviously, I can not speak for individuals with ASCs regarding how this change would impact them. A fascinating comment in the comment section of the prevous PBB article on this topic, however, provides an interesting perspective from an individual who reports having Asperger's syndrome and I highly recommend that you read the comment. No doubt, changing the Asperger's diagnosis such that it falls into an autism spectrum disorder continuum will confuse and frustrate some. Based upon the comment I just referenced, it also will provide relief to others. The question of the impact of this move, however, does not speak to the validity of the move. In other words, if changing the Asperger's diagnosis in this manner represents a more accurate description of the nature of ASC's but it causes distress, the problem is in the way we are educating individuals on the topic, not with the diagnostic shift. In this sense, it seems that providing awareness on these issues, which is always paramount, would simply become even more important should the DSM choose to make such a drastic change.
One point that Dr.Baron-Cohen made a few times in discussing this and with which I do agree is the idea that the Asperger's diagnosis is being "removed." Removal indicates that individuals who meet criteria for Asperger's would no longer meet criteria for a diagnosis and, as such, their symptoms would either not be assessed in the first place or not result in services being provided. This, however, is not the case. Individuals who met criteria for Asperger's using DSM-IV-TR criteria would simply meet criteria for autism spectrum disorder instead. Plus, as was mentioned in the previous NYT article, receiving services for an autism diagnosis is easier in most states than is receiving services for Asperger's and, as such, this shift does not seem like to result in a loss of services. Confusion is a legitimate consideration, but the disorder is not being removed and clarification of that point is not beyond the realm of possibility. Nonetheless, Dr.Baron-Cohen's point highlights an important underlying message - that changes to the diagnosis will impact a substantial number of people in a variety of ways, so clarity of message and purpose will be pivotal.
Point 3: Giving the scientific community time
I'm on the fence on this issue. I do agree with Dr.Baron-Cohen that we should be deliberate in our shifts and base them on evidence accumulated through systematic investigations of the issues. Doing so is a fundamental premise of scientific pursuit. That being said, how much time is enough time for scientists to uncover biological differences between ASC's that would justify keeping the subtypes separate in the face of mounting evidence that they are part of a single continuum? Additionally, to what degree are we making an unsubstantiated assumption that mental disorders all have a readily identifiable biological underpinning rather than an environmental or bi-directional cause? The concept of multi-finality - that several things can lead to the same outcome - speaks to the danger of waiting for the discovery of a single cause (this was, in fact, a major weakness of original versions of the DSM, which relied heavily upon psychodynamic theories of etiology in the absence of supportive evidence).
In a prior study, Dr.Baron-Cohen himself has indicated that ASC's exist along a continuous gradient of severity (Ring, Woodbudy-Smith, Watson, Wheelwright, & Baron-Cohen, 2008) and, in the NYT article this morning, he readily stated that he is one of the biggest believers in an autism spectrum. At the same time, he mentioned that he has recently published a study the reports on 14 genes associated with Asperger's. I was unable to find a copy of this study (if anyone has a copy and can direct me to a resource to find it, I would greatly appreciate it!), so it is unclear if these genes distinguished those with Asperger's from those with other ASC's (evidence that the spectrum diagnosis is unwarranted) or simply from individuals without an ASC (evidence that does not address the question at hand). It will be very interesting to learn more about that topic. Regardless, his position seems to be that there is reason to believe that more answers will emerge soon that would clarify this matter and that, as such, DSM-V is not the appropriate time for such a shift. Importantly, he is not saying that the shift should never be made, but rather that more evidence on the matter must be produced.
Summary
My goal today was to provide you with a perspective from an expert that goes somewhat against some of what we on PBB and others have said about potential shifts in autism spectrum diagnoses in DSM-V. As you can probably see, there are compelling arguments on both sides and many people who will be impacted regardless of the final decisions. My personal opinion is that we should go where the evidence leads us and that, as of now, the evidence is more consistent with a single continuum model. That being said, clearly there are highly informed, highly experienced individuals who think otherwise. Given the information presented on both sides, I am curious where you stand. Does the evidence support keeping these diagnoses separate from one another or is a continuous model more accurate? Regardless of accuracy, would the impact of the shift be harmful or are such fears based more on guesswork than evidence? Any thoughts that add to this conversation will be a welcome addition to the site.
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Mike Anestis is a doctoral candidate in the clinical psychology department at Florida State University
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