Saturday, March 28, 2009

Study Watch : Epidemiology of pervasive developmental disorders.

From the "la-la-la I can't hear you" department comes the latest work from Dr Eric Fombonne:

Epidemiology of pervasive developmental disorders.
There is evidence that the broadening of the concept, the expansion of diagnostic criteria, the development of services, and improved awareness of the condition have played a major role in explaining this increase, although it cannot be ruled out that other factors might have also contributed to that trend.
If we are to believe the work of Dr Fombonne the reason that is seems like autism is increasing is:
  1. The expansion of diagnostic criteria
  2. The development of services
  3. Improved awareness
Otherwise known as the holy trinity of denial.  

So which came first - the expansion of the criteria, development of services or improved awareness?  Or was it a chicken and an egg, I can never remember.

To be fair, the first point above is semi-valid.  The diagnostic criteria for autism did change in 1994 and it did become broader - but not that broad.

The paper is a rehash of earlier studies filled with fancy statistics and analysis designed to make you doubt that the autism is increasing.  So the question that comes to my mind is why does iyt matter if autism is becoming more common?

I think that the real issue here is the underlying theory of what causes autism.  

If autism is not increasing then we can keep looking for the genetic smoking gun that is the culprit and no one can be held accountable.  

If autism is increasing then it cannot be mainly a genetic disorder.  If it is not a genetic disorder then something is "causing" it and people are going to start demanding answers. 

I think many people are afraid of that happening.  


  1. Hi
    This is a new manuscript on the topic of prevalence
    Encephale. 2009 Feb;35(1):36-42. Epub 2008 Sep 23.
    [Prevalence of pervasive developmental disorders. A review.][Article in French]
    Lenoir P, Bodier C, Desombre H, Malvy J, Abert B, Ould Taleb M, Sauvage D.
    Service universitaire de psychiatrie de l'enfant et de l'adolescent, CHRU Bretonneau, 2 bis, boulevard Tonnellé, 37044 Tours cedex 09, France.

    INTRODUCTION: Estimates of the prevalence of autism and pervasive developmental disorders (PDD) are discordant and are moving towards an apparent increase in rates. LITERATURE REVIEW: The studies carried out since 1966 illustrate the variability of the protocols used and explanatory hypotheses put forward. These investigations are difficult, sparse, but still growing at the same time that a debate develops on the possible increase in actual prevalence. Indeed, the rate initially admitted for classic autism was 5/10,000, then 1/1000 with an expanded definition to the forms, but the current figures are very different (almost 0.7% for all PDD), and this increase raises questions. The arguments in favour of an apparent increase are primarily methodological. Several biases are encountered when one compares the recent publications with those of previous years. First, autism is better known and recognized than 30 or 40 years ago. Then, the diagnostic criteria used over time are changing variables, and comparisons difficult. Recent studies using the criteria of a broader definition of autism, polyhandicap with severe retardation and autism signs of lighter forms. The fact that children with autism are diagnosed more frequently in the younger age could also occasionally lead to an artificial increase in the number of cases identified in new surveys in populations of young children. Other factors are cited to explain the current increase. There could be higher rates of autism (and mental retardation) among children of migrants from distant countries, with the aetiological hypothesis of maternal infections, more frequent due to immune deficiency against infectious agents depending on the environment, metabolic decompensations also related to changes in surroundings, or more births from unions among migrant mothers and men with Asperger syndrome (with increased risk of paternity of a child with autism). Other theories relate to pollution, vaccinations, a growing number of premature babies; all assumptions that appear, for the time being, insufficiently explored and documented. The issue is also one of the motivations underlying these steps, and setting a parallel prevalence actually increased with this or that factor has presently been scientifically validated. Finally, if a careful reading of recent publications indicates that autism has become more frequent; assumptions that describe an increase in "artificial", based on methodological arguments, seem to be more consistent. EFFECTS OF EXTENSION OF DIAGNOSTIC CRITERIA AND NOSOGRAPHY FOR PDD: Today, the recruitment of individuals with autism in a population far exceeds the initial criteria of Kanner in the 1970's. It includes clinical forms with associated pathologies, or lighter and probably more frequent clinical forms. Other assumptions arouse interest, but also controversy regarding their relevance. The enumeration of cases of PDD in a population is actually at its beginning. In the 1970's, "childhood psychoses" (the term then used) seemed rare. The identification of cases was probably the main reason. Long available figures remain scarce, and their rate increases gradually from the 1990s, but is, in fact, a problem of inflation. What is the part played in this flight of changing diagnostic criteria and substitutions, or other methodological effects? Or even opportunistic effects, if we speak of an epidemic to undermine a variety of factors. The evidence provided so far is the improved identification of cases, enlargement of the concept, and better shared diagnostic criteria. However, the validity and limitations of clinical forms are still vague and unresolved. DISCUSSION: How to study epidemiology in the future - to move forward, studies should be designed with partners' medical history and medicosocial studies, based on a better consensual methodology, epidemiology, statistics and diagnosis, with a definition of the thresholds for inclusion, and arbitration procedures. On this basis, a study must also be coordinated with those concerning mental retardation, learning disorders, etc, otherwise the same topics will be counted twice or even three times. As for the addition of syndromic forms of PDD (those with known aetiology), their number is still below a proportion sufficient to be an appeal. Moreover, another problem exists: the degree of membership of each of these syndromes, or individual cases, or autistic spectrum disorders (internal variability phenotypes). For the moment, we could design two studies included better: developmental disorders and associated pathologies. Regarding the "ethic" dimension, a more regular diagnosis of PDD (preferred to that of mental retardation or learning disorder) will lead to shared practices and set limits for greater recognition

  2. And about the problem of misdiagnosis and the lack of awareness of the concomitant medical problems in ASD, an example
    Cell Mol Biol (Noisy-le-grand). 2009 Feb 16;55(1):19-22.Links
    Awareness is the name of the game: clinical and biochemical evaluation of a case of a girl diagnosed with acute intermittent porphyria associated with autism.Luder AS, Mamet R, Farbstein I, Schoenfeld N.
    Department of Pediatrics and Genetics Service, Ziv Medical Centre, Safed, Israel.

    Neuroporphyrias, a heterogeneous group of metabolic diseases, are diagnosed less often than their true prevalence justifies. Lack of awareness of porphyrias and their protean clinical and biochemical manifestations, is the most significant hurdle to their recognition and diagnosis. These points are reflected in the unusual case reported here, which highlights the potential damage that inappropriate management may cause when the diagnosis is missed over a long period. We diagnosed heterozygous Acute Intermittent Porphyria (AIP) in a 15 yr old girl, who first presented with autism at the age of 4 years. This phenotypic association has not been previously reported. In addition to the unrecognized phenotype, her normal urinary aminolevulinic acid and porphobilinogen, findings which are not compatible with symptomatic porphyria according to well established criteria, could also have led to a missed diagnosis of neuroporphyria. However, the diagnosis of AIP was established on the basis of a 64% reduction in erythrocyte hydroxymethylbilane synthase (HMBS) activity and the finding of a known causative AIP mutation (p.D178N). We therefore recommend that porphyria should be considered in autistic children especially when there is an atypical course or unexpected abreaction to medications. The biochemical and genetic data should be carefully evaluated in a specialized porphyria center

  3. Thanks, I will have to take a look at these.