Isobutyryl-CoA dehydrogenase deficiency, also called IBDD, is an extremely rare inherited inborn error of metabolism (IEM) of valine metabolism. It is an autosomal recessive disorder that is caused by a defective isobutyryl-coenzyme A dehydrogenase. Approximately 30 people have been identified with this condition, although the frequency may be much higher since it is relatively asymptomatic. Isobutyryl-coenzyme A dehydrogenase is a mitochondrial protein that belongs to the acyl-CoA dehydrogenase family of enzymes. Its main function is to catalyze the dehydrogenation of acyl-CoA derivatives in the metabolism of branched-chain amino acids, specifically valine. This enzyme is responsible for the third step in the breakdown of valine and converts isobutyryl-CoA into methylacrylyl-CoA. Defects in the IBD enzyme function lead to elevated levels of valine in blood and other biofluids (valinemia). IBDD can be identified by elevated levels of C4-acylcarnitine via newborn screening. Most people with IBDD are asymptomatic. Some individuals with IBDD have developed features such as a weakened and enlarged heart (dilated cardiomyopathy), weak muscle tone (hypotonia), and developmental delay. This condition may also result in low numbers of red blood cells (anemia) and very low levels of carnitine in the blood, which is a compound that plays a role in converting certain foods into energy. Symptoms may be worsened by long periods of fasting or infections that increase the body's demand for energy. Treatment may include the use of L-carnitine supplements, frequent meals, and a low-valine diet.
Valine, Leucine, and Isoleucine Degradation References
Lehninger, A.L. Lehninger principles of biochemistry (4th ed.) (2005). New York: W.H Freeman.
Salway, J.G. Metabolism at a glance (3rd ed.) (2004). Alden, Mass.: Blackwell Pub.
Wanders RJ, Duran M, Loupatty FJ: Enzymology of the branched-chain amino acid oxidation disorders: the valine pathway. J Inherit Metab Dis. 2012 Jan;35(1):5-12. doi: 10.1007/s10545-010-9236-x. Epub 2010 Nov 23.
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