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Gamma-aminobutyric acid (GABA) in CSF – Free and Total




Gamma-aminobutyric acid (GABA), a primary inhibitory neurotransmitter in the brain, is synthesized from glutamate by the pyridoxine dependent enzyme glutamic acid decarboxylase (GAD).  The first step in the catabolism of GABA involves degradation to succinic semialdehyde in a reaction catalyzed by GABA-transaminase (GABA-T). Succinic acid is then converted to succinic semialdehyde by the enzyme succinic semialdehyde dehydrogenase (SSADH).  GABA is also present in non-neuronal tissues and may exist in peripheral and central tissues in the form of a dipeptide with histidine, as a compound known as homocarnosine.  Several inherited disorders of GABA metabolism have been identified; these are SSADH deficiency, GABA-T deficiency and homocarnosinosis. The later two are extremely rare and require CSF determination of both free and total GABA.  The clinical presentation of these cases may vary considerably and include psychomotor retardation, convulsions, ataxia, hypotonia, hyperflexia and delayed speech development.  In addition an autosomal recessive disorder has been characterized in a group of patients with pyridoxine-dependent seizures.  In these cases the presumed abnormality is due to reduced binding of pyridoxal-5-phosphate to GAD. Elevation of CSF free and total GABA are characteristic of GABA-T and SSADH deficiency, where-as low CSF GABA has been reported in pyridoxal-5-phosphate dependent seizures.



Download Protocol Sheet and Test Requisition







·         CSF – 0.5 mL collected in a sterile container and frozen at -80˚C; minimum volume – 250uL.

      SPECIAL NOTE: Can be performed using Tube #5 from Special Collection tubes/kit – separate collection not necessary

·         If the sample is not blood contaminated, place the sample on ice (or dry ice if available) at the bedside.  Transfer the sample to a -80˚C freezer ASAP.

·         If the sample is blood contaminated, the sample tube should immediately be centrifuged (prior to freezing) and the clear CSF transferred to new similarly labeled tube then frozen and stored at -80˚C ASAP.

·         Store at -80C until sample transport


Ship sample Monday through Thursday only.
Ship sample overnight with 3-4 lbs of dry ice using a guaranteed overnight courier.

CPT Codes:


Turnaround Time:

10 business days from sample receipt 



Baylor Health Care System is located in Dallas, Texas