As I’ve said before, “autism” <<used to be>> a very rare medical diagnosis. Back in med school (~200 years ago), and for as long as I saw pediatric patients clinically (up to 1982)––among perhaps 10,000 kids––I recall seeing for certain one autistic boy. Back then, the diagnosis was very rigorous: the patient did not “see” or comprehend persons around him, but was very much aware, even skillful, with machines and other physical/mechanical items in his immediate environment. Also, I recall seeing saw at least one idiot savant for certain, but that disorder was distinctly different from autism.
More recently, it was decided to combine a basketful of “odd clinical presentations” associated with cognitive defects, and call the whole thing autism spectrum disorder (ASD). Today, as many as one-third of schoolroom classes comprise children with ASD (plus another attention problem called attention deficit/hyperactivity disorder; ADHD). Thus, in Western society, this amazingly rapid rise in frequency of ASD and ADHD is similar to that for obesity and type-2 diabetes; this increased rate in a population is far too rapid to expect DNA alteratins (mutations) to be the cause. More likely, these phenotypes (multifactorial traits) represent the contribution of hundreds if not thousands of small-effect genes, plus epigenetic effects––and probably exposure to environmental factors (which might include mother’s diet during the pregnancy, child’s diet, or even too much adverse stimulation by watching excessive TV or playing computer games).
Cognitive defects in ASD now include problems in socialization and communication: key behavioral capacities that separate humans from other species. In the attached article and editorial, authors analyze gene expression in the prefrontal cortex of 63 autism patients and control individuals––as well as 62 chimpanzees and macaques, from neonatal to adult age. They show that, among all aberrant expression changes seen in ASD brains (and not non-human hominid brains), a single aberrant expression pattern, … over-represented in genes involved synaptic-related pathways, … is enriched in nucleotide variants linked to autism. Furthermore, only this pattern contains an excess of developmental expression features unique to humans, thus resulting in the disruption of human-specific developmental programs in autism. Several members of the early growth response (EGR) transcription factor family can be implicated in regulation of this aberrant developmental change. This interesting study draws a connection between the genetic risk architecture of autism and molecular features of cortical development––that is unique to humans.
PLoS Biol Sept 2o16; 14: e1002558 and Editorial, p. e2000958