By Monica Heger

News has already emerged that the American Psychiatric Association is considering expanding its definition of autism to include a broader range of developmental and mental syndromes in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders. But under the radar, geneticists are moving in the opposite direction, parsing the disease into more specific subtypes on the basis of its molecular etiology.

Autism is not a biological disorder, but rather a behavioral description, with the underlying disease “a constellation of rare genetic disorders,” says John Spiro, the senior associate director for research at the New York–based Simons Foundation Autism Research Initiative. Last month, Spiro spoke at the first international symposium on a genetic subtype of autism known as Phelan-McDermid syndrome, an event that took place at the New York Academy of Medicine.

Stephen Scherer, director of the Centre for Applied Genomics at The Hospital for Sick Children in Toronto echoes Spiro’s view, saying that autism may in fact be a “bunch of different genetic disorders that have a common clinical outcome.”

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