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Table 5 Potential biomarker measures in fragile X syndrome

From: Updated report on tools to measure outcomes of clinical trials in fragile X syndrome

Domains Potential outcome Measure Shorter term Longer term Quality of tools
Blood and tissue
FMR1/FMRP expressiona FMR1 methylation Yes Yes + [9, 113, 261]
FMRP levels Yes Yes + [9, 113]
Signaling pathway
  ERK activation rate Yes Yes + [54, 55, 200, 203]
BDNF level Yes Yes + [159, 204, 208]
APP and metabolites levels Yes Yes + [159, 209]
MMP activity Yes Yes + [87, 227]
mTOR activity Yes Yes + [269]
S6 Kinase activity Yes Yes + [269]
Neurophysiological
  Electroencephalogram Yes   +[217, 218, 227, 228, 232, 233]
Event-related potentials Yes Yes +/++ [219, 222224, 227230]
Prepulse inhibition (PPI) Yes   +/++ [6, 117, 226]
Eye tracking and pupillometry Yes   ++ [77, 8588, 139, 216]
Neuroimaging MRI    
 sMRI Yes Yes + [235]
  -vMRI Yes Yes + [237240]
  -DWI Yes Yes + [241243]
 Functional MRI    
  -fMRI Yes Yes + [244250]
  -rs-fMRI Yes Yes + [77]
  -MRS Yes Yes + [270]
  -pMRI Yes Yes + [234]
NIRS Yes   + [251255]
  1. Abbreviations: FMR1 fragile X mental retardation 1 gene, FMRP fragile X mental retardation protein, ERK extracellular signal-related kinases, BDNF brain-derived neurotrophic factor, APP amyloid precursor protein, MMP matrix metalloproteinases, mTOR mechanistic target of rapamycin, MRI magnetic resonance imaging, pMRI perfusion MRI, sMRI structural MRI, vMRI volumetric MRI, DWI diffusion-weighted imaging, fMRI functional MRI, rs-fMRI resting state fMRI, MRS magnetic resonance spectroscopy, NIRS near-infrared spectroscopy, Shorter term deemed suitable for clinical trials lasting <12 months, Longer term deemed suitable for clinical trials lasting >=12 months. Grading system: +++ strong evidence, ++ moderate evidence, + limited evidence, ? unknown due to poor methodological quality, blank cell no evidence available
  2. aEvaluated as a predictor of response