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Glutaric aciduria type 1
GA1 is a rare genetic disorder that affects how the body processes certain proteins. If untreated, it can lead to the build-up of harmful substances, potentially causing brain damage, particularly in children.
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Overview
Glutaric aciduria type 1 (GA1) is a rare inherited metabolic disorder. It occurs when the body lacks a specific enzyme, glutaryl-CoA dehydrogenase, which is essential for breaking down certain amino acids: lysine, hydroxylysine, and tryptophan [PMID:33678077]. Without this enzyme, harmful substances, particularly glutaric acid and 3-hydroxyglutaric acid, can accumulate in the body. This build-up is toxic, especially to parts of the brain involved in movement and coordination.
GA1 is typically identified early in life, often through newborn screening programmes in the UK. Early diagnosis and treatment are crucial to prevent severe neurological complications. The estimated prevalence of GA1 ranges from 1 in 30,000 to 1 in 100,000 live births [PMID:32655450].
Symptoms & clinical features
The symptoms of GA1 can vary significantly between individuals. Some people might have no symptoms for a long time, while others can experience severe issues early in life. The most common presentation is a 'metabolic crisis', often triggered by an illness, fever, or lack of food, which can lead to neurological damage. Without early intervention, this damage can be irreversible.
Typical symptoms that may arise during a metabolic crisis include poor feeding, vomiting, irritability, and reduced muscle tone (hypotonia). Over time, if left untreated, affected individuals may develop movement disorders, such as dystonia (involuntary muscle contractions) and choreoathetosis (uncontrolled, jerky movements). Macrocephaly (a larger than average head circumference) may also be present from birth [PMID:33678077].
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Affected organs
Glutaric aciduria type 1 primarily affects the brain, particularly specific regions called the basal ganglia. These areas are crucial for controlling movement and are highly sensitive to the toxic effects of glutaric acid and 3-hydroxyglutaric acid accumulation. Damage to these brain regions can result in the neurological symptoms described previously.
While the brain is the primary organ affected, the metabolic imbalance from GA1 impacts the body's overall energy production and waste removal systems. Early diagnosis and management aim to protect the brain from these harmful effects.
Risks & severity
The severity of GA1 can vary widely. Some individuals, particularly those identified early through newborn screening and managed with diet, may have a good prognosis and avoid severe neurological problems. However, if diagnosis is delayed or treatment is inconsistent, there is a significant risk of irreversible brain damage, particularly after a metabolic crisis. Without treatment, approximately 90% of children with GA1 may develop neurological dysfunction [PMID:28763529].
The onset of severe symptoms typically occurs between 3 months and 3 years of age, often following an infectious illness. Lifelong dietary management and careful monitoring are necessary to minimise the risk of complications. The long-term outlook usually depends on how well the condition is managed, particularly the prevention of metabolic crises.
Genetic causes
Glutaric aciduria type 1 is caused by changes (variants) in the GCDH gene. The GCDH gene provides instructions for making an enzyme called glutaryl-CoA dehydrogenase. This enzyme plays a vital role in metabolising the amino acids lysine, hydroxylysine, and tryptophan, which are building blocks of protein.
When pathogenic variants occur in the GCDH gene, the glutaryl-CoA dehydrogenase enzyme either does not work correctly or is produced in insufficient amounts. This leads to a build-up of glutaric acid and 3-hydroxyglutaric acid, which are toxic metabolites, especially for the brain. The specific location and type of variant in the GCDH gene can influence the enzyme's residual activity and potentially the severity of the condition.
- GCDH glutaryl-CoA dehydrogenaseThe GCDH gene provides instructions for producing the glutaryl-CoA dehydrogenase enzyme, essential for breaking down specific amino acids within the body's cells.
Inheritance pattern
Glutaric aciduria type 1 is inherited in an autosomal recessive pattern. This means that for a person to develop GA1, they must inherit two copies of the altered GCDH gene - one from each parent.
If both parents are 'carriers' of a pathogenic GCDH variant, meaning each has one altered copy and one typical copy of the gene, they usually do not show symptoms of the condition. However, with each pregnancy, there is a 1 in 4 (25%) chance that their child will inherit two altered copies and develop GA1, a 1 in 2 (50%) chance that their child will be a carrier like them, and a 1 in 4 (25%) chance that their child will inherit two typical copies and not be affected or a carrier.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
Diagnosis & testing
GA1 is typically diagnosed in the UK through the national newborn screening programme, which uses a 'heel prick' blood test to screen for several rare but serious conditions. If screening results suggest GA1, further investigations are carried out.
Diagnosis can be confirmed by measuring elevated levels of glutaric acid and 3-hydroxyglutaric acid in urine or blood plasma. Genetic testing, typically an R-code test available through the NHS Genomic Medicine Service, can then identify pathogenic variants in the GCDH gene to confirm the diagnosis. A clinical genetics service can arrange such testing and provide genetic counselling. Adults, or older children, who were not screened as newborns and present with related neurological symptoms might also undergo these diagnostic tests.
Management & lifestyle
Management of GA1 aims to prevent the accumulation of toxic metabolites and minimise the risk of neurological damage. This typically involves a lifelong specialised diet, restricted in lysine and tryptophan intake, often supplemented with L-carnitine. L-carnitine helps the body clear some of the toxic substances.
During times of illness or metabolic stress, a 'sick day regimen' is crucial, which usually involves increasing carbohydrate intake and reducing protein to prevent the body from breaking down its own proteins too quickly, which could trigger a metabolic crisis. Management occurs under the guidance of a specialist metabolic team, including dieticians and paediatricians, within the NHS. Regular monitoring of metabolic markers is undertaken to adjust treatment as needed. Genetic counsellors can provide support and information regarding the genetic aspects of the condition and family planning.
UK care pathway
In the UK, suspected or confirmed Glutaric aciduria type 1 cases are managed within specialist metabolic centres, often identified via the NHS Newborn Screening Programme. Referral to clinical genetics services is standard for confirmatory genetic testing (which may involve specific R-codes for gene panel testing) and genetic counselling. Genetic counsellors provide essential support, helping families understand the inheritance patterns, recurrence risks, and implications for relatives. This integrated approach ensures access to specialised medical care and genetic expertise.
Frequently asked questions
How does diet help manage Glutaric aciduria type 1?
A special diet for GA1 involves carefully limiting foods high in lysine and tryptophan, which are the amino acids the body struggles to process. By controlling the intake of these amino acids, it helps prevent the build-up of harmful substances in the body, protecting the brain.
What is a 'metabolic crisis' in GA1?
A metabolic crisis is a severe episode often triggered by illness, fever, or prolonged fasting. During this time, the body's metabolism is stressed, leading to a rapid increase in toxic substances that can cause significant and irreversible brain damage if not managed quickly.
Can Glutaric aciduria type 1 be cured?
There is currently no cure for GA1, but it can be effectively managed. With early diagnosis, strict dietary management, and prompt attention to 'sick day rules', many individuals can lead healthy lives and avoid the severe neurological complications associated with the condition.
If I have a child with GA1, what does this mean for future pregnancies?
As GA1 is autosomal recessive, if you have one child with the condition, both you and your partner are carriers. This means that for each future pregnancy, there is a 1 in 4 chance of having another child with GA1. Genetic counselling can provide detailed information and support for family planning.
Is Glutaric aciduria type 1 always serious?
The severity of GA1 varies. With early detection through newborn screening and consistent dietary management, many individuals may experience milder symptoms or even no severe neurological issues. Without treatment, however, it can lead to serious neurological damage.
References
- Boy N, Mühlhausen C, Maier EM. Recommendations for diagnosing and managing individuals with glutaric aciduria type 1: Third revision. Journal of inherited metabolic disease. 2023. PMID: 36221165
- Schuurmans IME, Dimitrov B, Schröter J. Exploring genotype-phenotype correlations in glutaric aciduria type 1. Journal of inherited metabolic disease. 2023. PMID: 37020324
- Vijan A, Khoshpouri P, Murphy AN. Glutaric Aciduria Type 1. Radiographics : a review publication of the Radiological Society of North America, Inc. 2023. PMID: 37856314
- Martín-Rivada Á, Palomino Pérez L, Ruiz-Sala P. Diagnosis of inborn errors of metabolism within the expanded newborn screening in the Madrid region. JIMD reports. 2022. PMID: 35281663
- Yoldas Celik M, Canda E, Yazici H. Glutaric aciduria type 1: Insights into diagnosis and neurogenetic outcomes. European journal of pediatrics. 2024. PMID: 39658645
- Gala F, Jain N, Salunke N. 소아 신경영상에서 보이는 비선천성 원인의 영상 소견: 임상 화보. Journal of the Korean Society of Radiology. 2026. PMID: 41669735
- Gürbüz BB, Yılmaz DY, Coşkun T. Glutaric aciduria type 1: Genetic and phenotypic spectrum in 53 patients. European journal of medical genetics. 2020. PMID: 32777384
- Cornelius LP, Raju V, Julin A. Pediatric Glutaric Aciduria Type 1: 14 Cases, Diagnosis and Management. Annals of Indian Academy of Neurology. 2021. PMID: 33911375