临床推理:一个年轻的成年人认知变化,步态困难和肾功能不全

Schematic of Intracellular Cobalamin Metabolism Cobalamin (Cbl) III is bound to transcobalamin (TC) in the blood. This complex is endocytosed into the cell. On entering the lysosome, Cbl III becomes unbound from TC. Cbl III then enters the cytosol and undergoes enzymatic reduction from Cbl III to Cbl II aided by MMACHC. Cbl II then undergoes adenosylation to form adenosylcobalamin (AdoCbl) in the mitochondrion and methylation to form methylcobalamin (MeCbl) in the cytosol, respectively. AdoCbl is a cofactor for methylmalonyl-CoA-mutase (MMUT), which catalyzes the conversion of L-Methylmalonyl-CoA (MMA-CoA) to succinyl-CoA. MeCbl is a cofactor in the conversion of homocysteine to methionine, mediated by the enzyme methionine synthase (MTR).⁷