GABA Transaminase Deficiency

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GABA-transaminase deficiency is caused by mutations (changes) in the ABAT gene which provides instructions for making the GABA-transaminase enzyme. This enzyme is responsible for breaking down a brain chemical (neurotransmitter) called GABA, when it is not needed. GABA normally helps with slowing down (inhibiting) brain cell activity to prevent the brain from being overloaded with too many signals.  

When mutations in the ABAT gene occur, it causes a shortage of functional GABA-transaminase enzyme. Due to this, GABA is not broken down properly which causes it and another molecule called beta-alanine to collect abnormally in the brain cells. This build up changes the balance between the brain’s neurotransmitters causing the neurological problems associated with GABA transaminase deficiency.  

Extra GABA also leads to abnormal release of a protein that is needed for growth of the body’s bones and tissues (growth hormone), which causes the accelerated linear growth sometimes associated with the condition.  

GABA-transaminase deficiency is a very rare inherited disorder. Only a small number of affected individuals have been reported. The exact prevalence of this disorder is unknown.  

Symptoms of this condition start in infancy and include:  

•  recurrent seizures (epilepsy)  
• uncontrolled limb movements (choreoathetosis)  
• exaggerated reflexes (hyperreflexia)  
• weak muscle tone (hypotonia)  
• excessive sleepiness (hypersomnolence)  
• faster growth in length in affected babies (accelerated linear growth) 
• feeding problems  
• not gaining weight as quickly as expected (failure to thrive)  
• impaired development 

Individuals with this condition usually do not survive past the first 2 years of life, however some live longer into childhood.  

Diagnosis for this condition involves looking at the individual’s medical history, symptoms and a physical examination. EEGs can also be used to help with a diagnosis.  

The diagnosis is confirmed by molecular genetic testing which will show mutations (changes) in the ABAT gene.  

Treatment for this condition are symptomatic & supportive. They aim to manage and alleviate individual symptoms and provide support for the patient and their families.  

GABA transaminase deficiency is an inherited condition. Humans have chromosomes made up of DNA. Genes are pieces of DNA that carry the genetic information. Each chromosome may have several thousand genes. We inherit chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instructions that determine a person’s characteristics, which are a combination of the parents.  

The pattern of inheritance of GABA transaminase deficiency is autosomal recessive. This means that carriers of the condition do not have the disorder because the other gene of this pair is working normally. Parents of children with GABA transaminase deficiency are carriers.   

When both parents are carriers, the risk to the baby in each pregnancy is  

• 25% chance (1 in 4) of developing the condition  
•  50% chance (1 in 2) for the baby to be a carrier of the condition  
•  25% chance (1 in 4) for the baby to have two working genes and neither have the condition nor be a carrier  

Genetic counselling can be requested to get a full explanation.  

References are available on request. Please contact us by phoning 0845 241 2173 or emailing contact@metabolicsupportuk.org [Resource Library No: GNT004].