By Darold Treffert, MD
Doctor Erika Nurmi and co-workers at Vanderbilt University recently, using genetic exploration and methods, were able to identify, and separate, a subset of persons with autism who shared savant skills from a much larger group of autistic persons who did not have such skills. Their paper, “Exploratory Subsetting of Autism Families Based on Savant Skills Improves Evidence of Genetic Linkage to 15q11-q13” appeared in the July, 2003 issue of the Journal of the American Academy of Child Adolescent Psychiatry.
In that paper they point out that as many as 20 genes may contribute to autism risk. Over-representation of certain genes on Chromosome 15q11-q13 has been thought previously to perhaps contribute to autism risk.
In this study 94 multiplex families (multiple affected members; mainly affected sibling pairs and their parents) were included. 21 families were identified as “savant skills-positive” and 73 families were identified as “savant skills-negative”. This corresponds generally with the relative scarcity of savant skills in autism. The study found “the subset of 21 savant-skills positive families yielded significantly increased evidence for linkage to 15q11-q13″…….families in which probands had few or no savant skills (n=73) showed no evidence of linkage.”
Since savant abilities are sometimes seen in autism, but also occur in other conditions, the investigators point out that their results indicate that savant abilities and autism may be genetically related, but not exclusively so. That is, savant-like skills (rote memory, arithmetic and calendar calculations, musical ability, visual-spatial ability and mechanical ability) can be seen in other disorders, and in even in non-disabled persons. They then point out that a disorder called Prader-Willi syndrome is due to a deletion on this same 15q11-13 chromsome, and some of the features of Prader-Willi syndrome and autism (including exceptional puzzle skills for example) overlap. From these observations they conclude: “These data could be explained by a gene (or genes) in the chromosome 15q11-13 region that, when perturbed, contributes to predispositon to a particular cognitive style or pattern on intellectual impairments and relative strengths. Precisely how those skills are manifested in a given individual may be influenced by a variety of environmental, and possibly, genetic factors.”
The researchers are caseful to point out that the presence or absence of savant-like skills was by parent reporting only, without specific testing qualitatively or quantitatively for such skills. And they are careful to point out also these findings need to be replicated in further studies. But the conclusion that “these results may suggest the possibility that the 15q11-q13 locus that contributes to autism may also be relavant to savants who are not autistic” is particularly interesting, and challenging.
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For more information, please contact:
Darold A. Treffert, MD
St. Agnes Hospital, Fond du Lac, Wisconsin
Clinical Professor, Department of Psychiatry
University of Wisconsin Medical School, Madison
Personal Web site: http://www.daroldtreffert.com