Autism Subtypes and Genetic Research. Autism diagnostic issues (Part I)
Posted Feb 19 2009 5:13pm
A review of: Fred R. Volkmar, Matthew State, Ami Klin (2009). Autism and autism spectrum disorders: diagnostic issues for the coming decade Journal of Child Psychology and Psychiatry, 50 (1-2), 108-115 DOI: 10.1111/j.1469-7610.2008.02010.x
Fred Volkmar, one of the most prominent autism researchers, and his team at Yale university, just released a provocative review of the issues affecting the diagnostic process in autism spectrum disorders. The core of this review deals with an issue that is of great interest to many in the autism community: the subtyping and categorization of the broader spectrum of autism. That is, are the current recognized categories (Autism, Asperger’s, and PDD-NOS) the most comprehensive, accurate, relevant, and useful subtypes?
As most of the issues raised by Volkmar are of significant interest to my readers, I decided to touch on as many issues as possible in 2 to 3 daily posts. Here is a summary of the first relevant issues:
About PDD subtypes:
… if PDD subtypes could be more strongly related to treatments or if speciﬁc etiologies or pathophysiological mechanisms can be used to guide treatment. At present, however, the issue of treatment building upon an individual’s proﬁle of strengths or weaknesses is more important than distinctions between autism, PDD-NOS or Asperger’s syndrome;
That is, traditionally, the issue of subtypes has not affected clinical practice as much as it has affected research, mostly because clinical work is inherently individualistic. For example, the recommendations for treatment provided by a neuropsychologist after a comprehensive assessment evaluation are based on the pattern of strengths and weaknesses unique to each child, and not necessarily based on whether the child was diagnosed with autism, asperger’s or PDD-NOS. However, as our understanding of subtypes increase (especially PDD-NOS subtypes), research on the best treatment interventions for specific subtypes will also advance. This will help clinicians further refine there recommendations, so that these are developed to reflect both, the persons' patterns of strengths and weaknesses as well as the diagnostic subtype observed.
Regarding Subtypes and Genetic Research
Advances in genetics have raised the important questions for future research in subtyping. It is well accepted that the combination of genetic heterogeneity and diagnostic uncertainty complicates efforts to identify autism genes (Gupta & State 2007). Consequently, it has been taken as axiomatic that the ability to deﬁne phenotypic subgroups reﬂecting more homogenous biological mechanisms will be crucial to successful efforts at illuminating autism risk alleles. In fact, recent progress in genetic research both supports and challenges this basic notion.
In sum, there is significant difficulty in findings specific gene markers that are consistently associated with autism, possibly due to the vast clinical diversity within the autism spectrum. Thus, some genes may be associated with one specific subtype but not with another - but since we don't fully understand the subtypes we can not fully explain the inconsistency with current genetic research. Efforts to help us understand these subtypes have been focused on the mapping of genes to endophenotyopes. Endophenotypes are a conglomeration of factors (symptoms, physical characteristics, clinical expression, etc) that are linked to specific genes. The authors argued however, that efforts based on endophenotypes alone have many limitations and other approaches will be needed. For example, by examining gene-by-environment interactions, researchers will be able to explore which combination of genes and environmental factors may be associated with different developmental trajectories leading to the development of different autism subtypes.