To investigate whether common neurobiological mechanisms underlie effects of autism susceptibility genes,we assayed both the immediate memory and reversal memory in mutants of multiple homologous such genes in Drosophila.We found that although showing mild immediate memory defects,all these mutants displayed a serve defect in reversal learning.In other words,much pronounced alteration was observed in cognitive flexibility than in learning among all homologous autism susceptibility genes examined.To determine mechanisms underlying such behavioral alteration,we chose to focus on fragile X mental retardation gene (fmr1),encoding a RNA-binding protein.