PYCR2

mitochondrial protein catalyzes the conversion of pyrroline-5-carboxylate to proline, which is the last step in proline biosynthesis.^[5] Loss of PYCR2 does not lead to a gross defect in mitochondrial protein synthesis, but loss of function of PYCR2 leads to increased apoptosis under oxidative stress.^[6]

hypomyelination, and reduced cerebral white-matter volume. Hypomyelination and the absence of wrinkly skin makes this condition distinct from that caused by previously reported mutations in the gene encoding PYCR2’s isozyme, PYCR1, suggesting a unique and indispensable role for PYCR2 in the human CNS during development. This is substantiated by the fact that PYCR2 mRNA is moderately expressed in the developing human brain, and in much higher forms than either of the other two isoforms. Although PYCR2 is an enzyme for proline biosynthesis, systemic deprivation of proline does not appear to be the pathogenetic mechanism of this condition, given that plasma amino acid analysis in two affected individuals did not show low proline levels. Furthermore, mitochondrial protein synthesis was not affected in PYCR2-deficient cells. Therefore, deficiency of proline, as a building block of proteins, might not be the major pathophysiology. However, proline has been reported as a non-enzymatic antioxidant that suppresses apoptosis, and therefore local proline biosynthesis in neurons might be important for neuronal protection against oxidative stress.^[6]