I was asked to see a baby with a positive newborn screen with anÂ elevation in C5 and mild elevation in C4 interpreted as being consistent with 2-methylbutyrylglycinuria. ThisÂ is not a disorder IÂ am familiar with, and the literatureÂ is somewhat scarce. While the first few reported patients had features such as autism or mental retardation, Â multiple subsequently reported individuals with a biochemical phenotype of 2- methylbutyrylglycinuria had only a biochemical, and not a clinical phenotype. A particular mutation is somewhat common in the Hmong population, and appears to be clinically asymptomatic. Thus, it is unclear if 2-MBGuria will join the ranks of asymptomatic biochemical abnormalities, or truly has a phenotype in some affected individuals. A good review by Alfardan et al., was published in Mol Genet Metab. 2010 Aug;100(4):333-8.
Hilary Vernon, MD PhD