3-Methylcrotonyl-CoA carboxylase deficiency also known as 3-Methylcrotonylglycinuria is an inborn error of leucine metabolism and is inherited through an autosomal recessive fashion.[1] 3-Methylcrotonyl-CoA carboxylase deficiency is caused by mutations in the MCCC1 gene, formerly known as MMCA, or the MCCC2 gene, formerly known as MCCB. MCCC1 encodes the a-subunits of 3-methylcrotonyl-CoA carboxylase[2] while MCCC2 encodes the b-subunits.[3] The clinical presentation of 3-Methylcrotonyl-CoA carboxylase deficiency is varied, even within members of the same family.[4]
Manifestations of 3-Methylcrotonyl-CoA carboxylase deficiency range from asymptomatic[5] to neonatal onset with extreme neurological symptoms[6] and even fatal cases.[7] 3-Methylcrotonyl-CoA carboxylase deficiency is diagnosed by increased 3-hydroxyisovaleric acid and 3-methylcrotonylglycine in the urine. 3-hydroxyisovalerylcarnitine is often found in both the urine and blood.
Over 90% of those diagnosed with 3-Methylcrotonyl-CoA carboxylase deficiency by newborn screening remain asymptomatic. The medical abnormalities that present in the few who do show symptoms are not always clearly related to 3-Methylcrotonyl-CoA carboxylase deficiency.[5] Manifestations of 3-Methylcrotonyl-CoA carboxylase deficiency vary even among family members who share a common environment and genetics.[4]
Genetics
The MCCC1 and MCCC2genes make protein subunits that come together to form an enzyme called 3-methylcrotonyl-CoA carboxylase. This enzyme plays an essential role in breaking down proteins from the diet. Specifically, the enzyme is responsible for the fourth step in processing leucine. If a mutation in the MCCC1 or MCCC2 gene reduces or eliminates the activity of 3-methylcrotonyl-CoA carboxylase, the body is unable to process leucine properly. As a result, toxic byproducts of leucine processing build up to harmful levels, damaging the brain and nervous system. This condition is inherited in an autosomal recessive pattern.[19]
Since genotype isn't predictive of phenotype,[5]DNA testing isn't necessary. However, DNA analysis may help confirm 3-Methylcrotonyl-CoA carboxylase deficiency when the diagnosis is uncertain.[9]
Symptoms can be reduced by avoiding leucine, an amino acid. Leucine is a component of most protein-rich foods; therefore, a low-protein diet is recommended. Some isolated cases of this disorder have responded to supplemental biotin;[22] this is not altogether surprising, consider that other biotin-related genetic disorders (such as biotinidase deficiency and holocarboxylase synthetase deficiency) can be treated solely with biotin. Individuals with these multiple carboxylase disorders have the same problem with leucine catabolism as those with 3-methylcrotonyl-CoA carboxylase deficiency.[23]
1 2 Holzinger, A. (June 1, 2001). "Cloning of the human MCCA and MCCB genes and mutations therein reveal the molecular cause of 3-methylcrotonyl-CoA: carboxylase deficiency". Human Molecular Genetics. 10 (12). Oxford University Press (OUP): 1299–1306. doi:10.1093/hmg/10.12.1299. ISSN1460-2083. PMID11406611.
1 2 3 4 Visser, Gepke; Suormala, Terttu; Smit, G. Peter A.; Reijngoud, Dirk-Jan; Bink-Boelkens, Margreet Th. E.; Niezen-Koning, Klary E.; Baumgartner, E. Regula (November 20, 2000). "3-Methylcrotonyl-CoA carboxylase deficiency in an infant with cardiomyopathy, in her brother with developmental delay and in their asymptomatic father". European Journal of Pediatrics. 159 (12). Springer Science and Business Media LLC: 901–904. doi:10.1007/pl00008366. ISSN0340-6199. PMID11131348. S2CID22543465.
1 2 Baykal, T.; Gokcay, G. Huner; Ince, Z.; Dantas, M. F.; Fowler, B.; Baumgartner, M. R.; Demir, F.; Can, G.; Demirkol, M. (2005). "Consanguineous 3-methylcrotonyl-CoA carboxylase deficiency: Early-onset necrotizing encephalopathy with lethal outcome". Journal of Inherited Metabolic Disease. 28 (2). Wiley: 229–233. doi:10.1007/s10545-005-4559-8. ISSN0141-8955. PMID15877210. S2CID23446678.
1 2 3 Bannwart, C.; Wermuth, B.; Baumgartner, R.; Suormala, T.; Wiesmann, U. N. (April 21, 1992). "Isolated biotin-resistant deficiency of 3-methylcrotonyl-CoA carboxylase presenting as a clinically severe form in a newborn with fatal outcome". Journal of Inherited Metabolic Disease. 15 (6). Wiley: 863–868. doi:10.1007/bf01800223. ISSN0141-8955. PMID1293382. S2CID10399688.
↑ Fries, Melissa H.; Rinaldo, Piero; Schmidt-Sommerfeld, Eberhard; Jurecki, Elena; Packman, Seymour (1996). "Isovaleric acidemia: Response to a leucine load after three weeks of supplementation with glycine, L-carnitine, and combined glycine-carnitine therapy". The Journal of Pediatrics. 129 (3). Elsevier BV: 449–452. doi:10.1016/s0022-3476(96)70081-1. ISSN0022-3476. PMID8804338.
↑ Rutledge, S. L.; Berry, G. T.; Stanley, C. A.; van Hove, J. L. K.; Millington, D. (March 30, 1994). "Glycine and L-carnitine therapy in 3-methylcrotonyl-CoA carboxylase deficiency". Journal of Inherited Metabolic Disease. 18 (3). Wiley: 299–305. doi:10.1007/bf00710419. ISSN0141-8955. PMID7474896. S2CID12833877.
↑ Naylor, Edwin W.; Chace, Donald H. (1999). "Automated Tandem Mass Spectrometry for Mass Newborn Screening for Disorders in Fatty Acid, Organic Acid, and Amino Acid Metabolism". Journal of Child Neurology. 14 (1_suppl). SAGE Publications: S4 –S8. doi:10.1177/0883073899014001021. ISSN0883-0738. PMID10593560. S2CID13459497.
↑ Schulze, Andreas; Lindner, Martin; Kohlmüller, Dirk; Olgemöller, Katharina; Mayatepek, Ertan; Hoffmann, Georg F. (June 1, 2003). "Expanded Newborn Screening for Inborn Errors of Metabolism by Electrospray Ionization-Tandem Mass Spectrometry: Results, Outcome, and Implications". Pediatrics. 111 (6). American Academy of Pediatrics (AAP): 1399–1406. doi:10.1542/peds.111.6.1399. ISSN0031-4005. PMID12777559.
↑ Beemer, F. A.; Bartlett, K.; Duran, M.; Ghneim, H. K.; Wadman, S. K.; Bruinvis, L.; Ketting, D. (1982). "Isolated biotin-resistant 3-methylcrotonyl-CoA carboxylase deficiency in two sibs". European Journal of Pediatrics. 138 (4). Springer Science and Business Media LLC: 351–354. doi:10.1007/bf00442517. ISSN0340-6199. PMID7128647. S2CID7949570.
1 2 Oude Luttikhuis, H. G. M.; Touati, G.; Rabier, D.; Williams, M.; Jakobs, C.; Saudubray, J. M. (2005). "Severe hypoglycaemia in isolated 3-methylcrotonyl-CoA carboxylase deficiency; a rare, severe clinical presentation". Journal of Inherited Metabolic Disease. 28 (6). Wiley: 1136–1138. doi:10.1007/s10545-005-4545-1. ISSN0141-8955. PMID16435207. S2CID21416887.
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