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Gamma-aminobutyric acid (free and total)

Download Test Requisition 

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 latter 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.






Liquid chromatography-tandem mass spectrometry



Sample Type:

CSF (0.5 mL) – Collected in standard CSF container or in a set of CSF collection tubes provided by Baylor IMD. One set of tubes is required per patient.



Sample Handling:

Follow the steps located on the Collection Protocol Sheet enclosed with the CSF collection set. If the samples are not blood contaminated, place the tubes on ice (dry ice, if available) at bedside. Transfer the samples to a -80⁰C freezer as soon as possible. If the samples are blood contaminated, centrifuge the tubes immediately (prior to freezing) and transfer the clear CSF to new collection tubes. Transfer the samples to a  -80⁰C freezer as soon as possible.




Ship sample Monday through Thursday with 3-4 pounds dry ice using an overnight trackable courier.



CPT Code:




Turnaround Time:

10 business days




Struys EA, Guérand WS, ten Brink HJ, Jakobs C. Combined method for the determination of gamma-aminobutyric and beta-alanine in cerebrospinal fluid by stable isotope dilution mass spectrometry. J Chromatogr B Biomed Sci Appl. 1999 Sep 10;732(1):245-9.





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