Autism and Asperger syndrome are both characterized by impaired communication skills, a desire for keenly focused stimuli and strong inclination toward repetition. They are distinguished only by a slower onset of language skills and latency of intelligence in autism, says Baron-Cohen. He further suggests that this distinction is proving not to be concrete enough, and that the DSM-V committee's struggle with the controversy can be attributed to the lack of physiological distinction of these psychiatric conditions.
I would agree with Baron-Cohen that there is not currently enough genetic distinction between autism and Asperger syndrome to warrant their being entirely separate conditions outside the spectrum disorders umbrella in the DSM-V. However, I think that defining Asperger syndrome idiosyncratically is important to preserve in the new manual. Here is why:
1) Baron-Cohen mentions his own group's recent identification of 14 Asperger-specific genes,19 genes specific to autism and 7 shared (Chakrabarti et al 2009). They measured 68 candidate genes in two experiments: the first measured autistic traits in an undiagnosed sample population using the Autism Spectrum Quotient; the second, using the Empathy Quotient. These two experiments were designed to identify autistic and Asperger cases among the sample:
"We searched for common genetic variants (single nucleotide polymorphisms (SNPs)) on the assumption that autistic traits are continuously distributed in the general population [Constantino & Todd, 2005; Sung et al., 2005]."
"In Experiment 1, autistic traits (measured on AQ and/or EQ) were nominally associated at P<0.05 with SNPs from 19 genes. In Experiment 2, SNPs from 14 genes were nominally associated at P<0.05 with AS."Six genes were nominally significant in both experiments. This study alone suggests that Asperger syndrome deserves a distinction as a sub-group in the Autism Spectrum Disorders (ASD) category that the DSM-V committee is considering, as opposed to eliminating it entirely, as is also being considered.
The Charkrabarti study is impressive, and the first step in the important attempt to identify the genetic and epigenetic correlates of autism and Asperger separately. However, there is still an extensive amount of correlative research to be done. A good amount of this is ongoing through the AutDB Project.
2) If for no other reason than to preserve the honor of the venerable Hans Asperger.
3) To keep company the solitary other recognized ASD, Pervasive Developmental Disorder - Not Otherwise Specified (PDD-NOS).* Perhaps these could both become sub-groups in the ASD category.
It is noteworthy that a great deal of genetic research already refer to their studies as ASD interactions/links/correlations (PubMed or Google Scholar this). I am terribly eager to find out whether or not this plays a strong role in the decision of the DSM-V committee.
*High- and Low-functioning autism are not classified as spectrum disorder subgroups, although they should be... and perhaps, one day, will be, provided there is a physiological distinction to be drawn between them, Asperger and PDD-NOS.