This morning's session at the Keystone meeting on the pathophysiology of autism in Santa Fe, New Mexico, focused on the disorder's link to Fragile X syndrome. Like autism, Fragile X is associated with behaviors such as high social anxiety, gaze avoidance, and speech problems. A significant number of people with Fragile X - estimates range wildly from 5 to 60% - have autism, but a smaller number of autistic cases are associated with Fragile X (maybe on the order of 4% of or so).

David Nelson from Baylor College of Medicine in Texas posed an interesting question: Why don't all Fragile X patients have autism? Are there stochastic, developmental, genetic modifiers? His group has tried to answer that question.

Fragile X syndrome results from a mutation in the FMR1, or fragile X mental retardation gene, which encodes the FMRP protein. But in most patients, this mutation is mosaic, leading his group to hypothesize that changes in the Fmr1 mutation may explain this variety in phenotype.

They found that FMR1-knockout mice (who also lacked a Fragile X related protein) had no circadian rhythm, even when exposed to light and dark. Nelson suggested that these findings show that the Fmr1 family helps control the body's internal clock, and changes to that family could underlie problems in learning and memory.