Diagnostic approach


 (J. Klepper, Aschaffenburg; updated 01.2007)

The biochemical hallmark of GLUT1 deficiency syndrome is a low glucose concentration in the cerebrospinal fluid (CSF), termed “hypoglycorrhachia”. This is determined in a fasting lumbar puncture. Absolute glucose values in CSF can be misleading as they directly relate to blood glucose concentrations. For instance, a CSF glucose of 30 mg/dl would be normal if blood glucose is 50 mg/dl (ratio 0,6), but indicative for GLUT1 deficiency syndrome if blood glucose is 100 mg/dl (ratio 0,3). Therefore hypoglycorrhachia is expressed as a ratio of CSF vs. blood glucose concentrations. A ratio of < 0.4 is indicative for GLUT1 deficiency syndrome. However, the value does not correlate to the severity of the disease.
 

 

   Quotient (Example):

   

normal

  GLUT1-Defekt
  CSF glucose:    60 mg/dl   30 mg/dl
  Blood glucose: 100 mg/dl   100 mg/dl
  ratio:     0,6              0,3

 

         

Important:

The lumbar puncture has to be performed in afasting state (4 - 6 hours fasting prior to the investigation), as changes in glucose concentrations are reflected much faster in blood than in brain.
Blood glucose should be determined before the lumbar puncture to avoid a stress-related elevation of this important parameter.
Always determine lactate in the cerebrospinal fluid 
(in GLUT1 deficiency syndrome it is always low to normal).

Cerebral imaging (CT, MRI) usually is uninformative. Brain malformations are not a feature of GLUT1 deficiency syndrome. Imaging of the glucose metabolism in the brain (PET) has been reported to show a pattern specific for GLUT1 deficiency syndrome.