title: The quest for fragile X biomarkers.
abstract: BACKGROUND
  Fragile X is the most common form of inherited intellectual disability and the leading known genetic cause of autism. There is currently no cure or approved medication for fragile X although various drugs target specific disease symptoms and a large number of therapeutics are in various stages of clinical development. Multiple recent clinical trials have failed on their primary endpoints indicating that there is a compelling need for validated biomarkers and outcome measures in fragile X.
  
  
  RESULTS
  There are currently no validated blood-based biomarkers to assess disease severity or to monitor drug efficacy in fragile X syndrome. Herein, we review candidate blood protein biomarkers including extracellular-regulated kinase, phosphoinositide 3-kinase, matrix metalloproteinase 9, amyloid-beta and amyloid-beta protein precursor.
  
  
  CONCLUSIONS
  Bench-to-bedside plans for fragile X syndrome are severely limited by the lack of validated outcome measures. The reviewed candidate biomarkers are at early stages of validation and deserve further investigation.
authors.affiliation: Department of Neurology, University of Wisconsin-Madison, Madison, WI, USA. westmark@wisc.edu.
authors.forename: Cara J
authors.initials: CJ
authors.lastname: Westmark
keywords: Amyloid beta protein precursor; Amyloid-beta; Biomarker; Extracellular-regulated kinase; Fragile X syndrome; Matrix metalloproteinase 9; Phosphoinositide 3-kinase