WP5028 - Glycine metabolism, including IMDs - Homo sapiens

The main disorder related to glycine (NonKetotic Hyperglycinemia, NKH) is a malfunctioning of the glycine cleavage enzyme, which consists out of four subunits (P-, H-, T- and L-protein). These subunits work together (however not as a complex) to convert glycine and H4-folate into methylene-tetrahydrofolate (CH2=folate), as depicted on the lefthand side of this pathway. This disorder is also known as glycine encephalopathy, with cerebral dysfunctioning as the common denominator. Besides "classical" NKH, there are several patients without mutations in the cleavage enzyme, however presenting variants within a protein related to the formation of lipoyl-H, as depicted on the righthand side of this pathway. The individual relationship between these proteins and the formation of iron-sulfur clusters (Fe-S) are not completely known, however there are indications that mutations within the NFU1, BOLA3 and GLXR5 gene can lead to a similar phenotype as NKH; most patients present with either less or more severe neurological symptoms compared to "classical" NKH. For clarity, the influence of pyridoxal-P has been added to this pathway, where a variant within the PNPO gene can lead to secondary effects on the activity of the P-protein from the cleavage system.

This pathway was inspired by Chapter 5 (edition 4) of the book of Blau (ISBN 3642403360 (978-3642403361)), Fig. 5.1.