What are the symptoms? Before birth, a baby with an organic acidaemia is usually protected from harm as the placenta is able to remove any harmful acids. Soon after delivery, these acids begin to accumulate and may cause a severe illness. Characteristic symptoms include: drowsinessreluctance to feedbreathing problems (usually fast breathing)vomitinghypotonia (floppiness)and/or spasticity (stiffness). What are the causes? In each condition, there is a deficiency of a particular enzyme involved in the breakdown of one or more amino acids due to a genetic change (mutation) that means the enzyme is not made properly. This leads to a build-up of harmful acidic chemicals in the body. Individual disorders are usually named after the type of chemical that accumulates in the blood or urine or, alternatively, according to the enzyme that is deficient. For example, in propionic acidaemia there is an accumulation of propionic acid in blood but the condition is also called propionyl-CoA carboxylase deficiency, since it is the enzyme propionyl-CoA carboxylase that is deficient. The other most common organic acidaemias are methylmalonic acidaemia and isovaleric acidaemia. How is it diagnosed? The diagnosis is most often made by finding high levels of characteristic chemicals in urine by a scientific technique called gas chromatography/mass spectrometry (GCMS) and in blood using another technique called tandem mass spectrometry (TMS). The diagnosis can then be confirmed by doing special enzyme studies and by DNA tests. Isovaleric acidaemia is now tested for on the new born heel prick test done on day 5 of life. How is it treated? Treatment is directed at trying to prevent the accumulation of the harmful acidic chemicals by reducing the intake of protein in the diet, while ensuring the diet is nutritionally complete, and increasing the removal of acidic chemicals using various medicines. The patients are also given an emergency regimen consisting of a glucose polymer drink that they must take when they are unwell. Unfortunately, there is no cure for any of the organic acidaemias because the defect in the manufacture of the particular enzyme is permanent and no effective enzyme replacement is yet available. Treatment may be effective in those with less severe symptoms but, unfortunately, for those with a more severe disease, long-term complications are common and may be life-threatening. Inheritance patterns and prenatal diagnosis Inheritance patternsThese conditions are inherited in an autosomal recessive manner and are life long. This means parents of children with an organic acidaemia will each have one normal and one abnormal gene. One normal gene makes enough enzyme so that parents do not have the disorder themselves. However, at the time of conception there is a 1 in 4 chance or 25% chance their baby will have inherited both the abnormal genes from his/her parents. Affected families should be referred to a genetics centre for advice and support. Prenatal diagnosisPrenatal testing is available. Testing is carried out using chorionic villus sampling but amniocentesis may also be used. Is there support? Information and support in the UK for organic acidaemias is provided by Metabolic UK (see entry Inherited Metabolic diseases).
What are the symptoms? Before birth, a baby with an organic acidaemia is usually protected from harm as the placenta is able to remove any harmful acids. Soon after delivery, these acids begin to accumulate and may cause a severe illness. Characteristic symptoms include: drowsinessreluctance to feedbreathing problems (usually fast breathing)vomitinghypotonia (floppiness)and/or spasticity (stiffness).
What are the causes? In each condition, there is a deficiency of a particular enzyme involved in the breakdown of one or more amino acids due to a genetic change (mutation) that means the enzyme is not made properly. This leads to a build-up of harmful acidic chemicals in the body. Individual disorders are usually named after the type of chemical that accumulates in the blood or urine or, alternatively, according to the enzyme that is deficient. For example, in propionic acidaemia there is an accumulation of propionic acid in blood but the condition is also called propionyl-CoA carboxylase deficiency, since it is the enzyme propionyl-CoA carboxylase that is deficient. The other most common organic acidaemias are methylmalonic acidaemia and isovaleric acidaemia.
How is it diagnosed? The diagnosis is most often made by finding high levels of characteristic chemicals in urine by a scientific technique called gas chromatography/mass spectrometry (GCMS) and in blood using another technique called tandem mass spectrometry (TMS). The diagnosis can then be confirmed by doing special enzyme studies and by DNA tests. Isovaleric acidaemia is now tested for on the new born heel prick test done on day 5 of life.
How is it treated? Treatment is directed at trying to prevent the accumulation of the harmful acidic chemicals by reducing the intake of protein in the diet, while ensuring the diet is nutritionally complete, and increasing the removal of acidic chemicals using various medicines. The patients are also given an emergency regimen consisting of a glucose polymer drink that they must take when they are unwell. Unfortunately, there is no cure for any of the organic acidaemias because the defect in the manufacture of the particular enzyme is permanent and no effective enzyme replacement is yet available. Treatment may be effective in those with less severe symptoms but, unfortunately, for those with a more severe disease, long-term complications are common and may be life-threatening.
Inheritance patterns and prenatal diagnosis Inheritance patternsThese conditions are inherited in an autosomal recessive manner and are life long. This means parents of children with an organic acidaemia will each have one normal and one abnormal gene. One normal gene makes enough enzyme so that parents do not have the disorder themselves. However, at the time of conception there is a 1 in 4 chance or 25% chance their baby will have inherited both the abnormal genes from his/her parents. Affected families should be referred to a genetics centre for advice and support. Prenatal diagnosisPrenatal testing is available. Testing is carried out using chorionic villus sampling but amniocentesis may also be used.
Is there support? Information and support in the UK for organic acidaemias is provided by Metabolic UK (see entry Inherited Metabolic diseases).