Synonyms: glutaric aciduria, glutaryl-CoA dehydrogenase deficiency (type I GA), electron transport flavoprotein deficiency and electron transport flavoprotein oxoreductase deficiency (both type II GA), multiple Acyl-CoA dehydrogenase deficiency (MADD – synonymous with type II GA), glutaryl-CoA oxidase deficiency (type III GA)
Glutaric acidaemias (GAs) are rare inborn errors of metabolism. They are caused by a heterogeneous group of mutations that impair either mitochondrial (types I and II) or peroxisomal (type III) metabolism. Glutaryl-CoA dehydrogenase (deficient in type I GA) plays a key role in the metabolism of lysine, hydryoxylysine and tryptophan. The affected enzymes in type II GA are intimately involved in fatty acid, amino acid and choline metabolism. Peroxisomes are ubiquitous single-membrane organelles responsible for the sequestration and activity of key metabolic enzymes, present in nearly all eukaryotic cells. They play an important role in the metabolism of long-chain and very long-chain fatty acids, the biosynthesis of plasmalogens, cholesterol synthesis, bile acid synthesis, amino acid metabolism and purine metabolism.
Classification of glutaric acidaemia
- Type I GA
- Autosomal recessive inheritance.
- High incidence in 'genetically closed' communities, particularly the Amish community in USA.
- Gene located on short arm of chromosome 19.
- Causes microencephalic macrocephaly in neonates and acute damage to the basal ganglia (striatum and putamen) causing severe dystonia and episodes of encephalopathy.
- Type II GA
- Type III GA
- Exceedingly rare sporadic condition with no defined chromosomal location (<10 reported cases).
- Causes disease in neonates or young children.
- Presents as dysmorphia, failure to thrive and other varied abnormalities.
- Type I – very rare. In the Republic of Ireland there were 21 patients identified in the country over a 16-year period. High incidence in the Amish community in the USA (carrier frequency approximately 10%).
- Type II – incredibly rare. No reliable population-based figures.
- Type III – exceedingly rare. A handful of reported cases.
- The earliest presentation in neonates is microencephalic macrocephaly (small brain in big head), which causes disruption of intracerebral bridging veins; this may lead to subdural haematoma and retinal haemorrhage in newborns.
- Failure to thrive, hypotonia and hypoglycaemia are other features.
- It may damage the basal ganglia. Acute striatal necrosis in infancy is the main cause of morbidity associated with the condition. The damage is like a stroke in its sudden evolution and CT appearance. It leads to severe dystonia and progressive athetosis that may cause oromotor, gastro-oesophageal, skeletal and respiratory complications. Where the putamen is damaged, it causes abrupt onset behavioural arrest.
- Spastic diplegia and cerebral palsy are possible modes of presentation.
- Secondary carnitine deficiency may cause episodes of encephalopathy triggered by infection or fasting, which may present with lethargy, seizures, apnoea, hypotonia, hepatomegaly and cardiac failure.
- Although it is commonly a disease of infancy there are patients who appear to have milder forms of the disease that present in later childhood. Exercise intolerance, hypoglycemia and seizures can be features of illness in older patients.
- May cause severe or fatal neonatal acidosis with mustiness of the breath, often described as similar to the smell of sweaty feet.
- There is usually a propensity to episodic hypoglycaemia in infancy and childhood, with muscular hypotonia and/or respiratory distress.
- Fatty infiltration and damage to the liver is often present.
- May present as dysmorphia or with renal or cardiac anomalies.
- There is a great degree of variability in severity and some patients may not have symptoms until they are in their teenage years, when muscular problems, such as proximal myopathy, are the usual mode of presentation.
- Presents in a variable fashion depending upon the particular cause of the genetic problem (the condition seems to be caused by chromosomal abnormalities and may co-exist with other diseases such as thalassaemia).
- Failure to thrive, dysmorphia, bowel disorders and thyroid dysfunction are some of the possible modes of presentation of this very rare disease.
- A large number of other inborn or acquired errors of metabolism may cause similar symptoms and biochemical derangement. Specialist analysis of biochemical and genetic information is needed to distinguish between the numerous possibilities.
- Child abuse may initially be suspected in some cases of type I GA due to the presence of intracerebral bleeding, causing a suspicion of shaken-baby syndrome.
- Blood and urine levels of glutarate and 3-hydroxyglutarate are grossly elevated in all types of GA, as detected by direct assay or gas-liquid chromatography.
- There are also low blood levels of carnitine and acylcarnitine.
- In type II GA there is a range of abnormal organic acids in the blood and urine.
- Biopsy of muscle and liver may be required.
- The biochemical response to riboflavin and carnitine or lysine loading may help in making the diagnosis.
- Estimation of enzyme activity in cultured fibroblasts may be used.
- The mainstays of ameliorative therapy are careful dietary manipulation, treatment with riboflavin and supplementation of L-carnitine. This helps to enhance enzymatic function and overcome the sequelae of the secondary carnitine deficiency.
- Early identification, particularly of type I GA, is crucial so that this therapy can be given before neurological damage occurs, which is irreversible.
- Careful highly-specialist management of episodes of illness or anaesthesia is necessary in type I GA to prevent acute neurological damage or encephalopathic crises.
- Muscular weakness or dystonia
- Basal ganglia damage
- Spastic diplegia and cerebral palsy
- Fluid and blood collections in the cranium due to bridging vein disruption
- Acute or chronic metabolic acidosis
- Liver damage
- Episodic encephalopathy
- Severe illness and death
- For type I GA the overall long-term outlook is fairly poor, with death or severe disability a likely outcome before adulthood in most cases.
- Individual outcomes are highly variable depending on the degree of phenotypic expression of the heterogeneous genetic abnormalities.
- Earlier recognition of the disease, particularly in high-risk groups such as the Amish, combined with advanced specialist treatment, are improving the situation in terms of survival and disability.
- The outlook in type II GA is poor in those affected in childhood, but some cases have responded well to riboflavin therapy.
- Type III GA carries a grave prognosis, with death during neonatal period or infancy being the usual outcome.
- It is possible to screen newborns for the type I form of the disease using tandem-mass-spectrometry analysis of heel-prick blood that is routinely taken to screen for other inborn errors of metabolism.
- This technique is being employed in high-risk populations such as the Amish, and may help to reduce the burden of neurological disease caused by the condition, through the institution of early dietary manipulation and supplementation.
- Population-based screening is not currently employed due to the rarity of the condition.
Further reading and references
; Peroxismal disorders. eMedicine, March 2007.
; The peroxisome website Excellent overview of peroxisomal function and disorders tailored to needs of laypeople, scientists and physicians.
; Glutaric aciduria type I: outcome in the Republic of Ireland. J Inherit Metab Dis. 2004
; Overview of genetic, biochemical and clinical knowledge
; Type I glutaric aciduria, part 1: natural history of 77 patients. Am J Med Genet C Semin Med Genet. 2003 Aug 15121(1):38-52.
; Carnitine Deficiency eMedicine, July 2009.
; So doctor, what exactly is wrong with my muscles? Glutaric aciduria type II presenting in a teenager. Neuromuscul Disord. 2006 Apr
; Glutaric aciduria types I and II. Brain Dev. 2006 Apr
; Neonatal screening for glutaric aciduria type I: Strategies to proceed. J Inherit Metab Dis. 2006 Apr
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