Organic acidemia


Organic acidemia, also called organic aciduria, is a term used to classify a group of metabolic disorders which disrupt normal amino acid metabolism, particularly branched-chain amino acids, causing a buildup of acids which are usually not present.


* Malaise * Refusing food * Breathing problems * Reduced muscle tone * Vomiting


Most of the organic acidemias result from defective autosomal genes for various enzymes important to amino acid metabolism. Neurological and physiological harm is caused by this impaired ability to synthesize a key enzyme required to break down a specific amino acid, or group of amino acids, resulting in acidemia and toxicity to specific organs systems. Most are inherited as autosomal recessive diseases.


In all types of organic acidemia, diagnosis cannot be made by simply recognizing the outward appearance of symptoms. Instead, diagnosis is usually made by detecting abnormal levels of organic acid cells in the urine through a urinalysis. The specific test used is called combined gas chromatography-mass spectrometry. In gas chromatography, a sample is vaporized and its components separated and identified. Mass spectrometry electronically weighs molecules. Every molecule has a unique weight (or mass). In newborn screening, mass spectrometry analyzes blood to identify what amino acids and fatty acids are present and the amount present. The results can identify if the person tested has a specific organic acidemia. Many organic acidemias also can be diagnosed in the uterus by using an enzyme assay of cultured cells, or by demonstrating abnormal organic acids in the fluid surrounding the fetus. In some laboratories, analysis is done on blood, skin, liver, or muscle tissue. Molecular DNA testing is also available for common mutations of MCAD and LCHAD. Since most organic acidemias are rare, routine screening of fetuses or newborns is not usually done and is not widely available. In MCAD, a more common organic acidemia, abnormal organic acids are excreted in the urine intermittently so a diagnosis is made by detecting the compound phenylpropionylglycine in the urine.


The prognosis of patients with organic acidemias varies with each disorder and usually depends on how quickly and accurately the condition is diagnosed and treated. Some patients with organic acidemias are incorrectly diagnosed with other conditions, such as sudden infant death syndrome (SIDS) or Reye syndrome. Without a quick and accurate diagnosis, the survival rate decreases with each episode of the disorder. Death occurs within the first few years of life, often within the first few months. With a quick diagnosis and aggressive monitoring and treatment, patients can often live relatively normal lives. For example, children with either biotinidase deficiency or holocarboxylase synthetase deficiency, when detected early and treated with biotin, have generally shown resolution of the clinical symptoms and biochemical abnormalities.


Treatment or management of organic acidemias vary. There are no effective treatments for all of the conditions, though treatment for some may include a limited protein/high carbohydrate diet, intravenous fluids, amino acid substitution, vitamin supplementation, carnitine, induced anabolism, and in some cases, tube-feeding.