The Kidney in Methylmalonic Acidaemia

Different inherited metabolic diseases in the cobalamin pathway show a heterogenous kidney involvement. Isolated methylmalonic acidaemias are caused by defects in the genes MMUT, MMAA, or MMAB and are characterized by the accumulation of methylmalonic acid in blood and urine. Possibly due to toxic metabolite effects and a mitochondrial energy deficiency, these disorders result in tubulointerstitial nephritis and progressive kidney failure. Defects elsewhere in the cobalamin pathway, namely, in the genes MMACHC and MTR, can cause hemolytic uremic syndrome. Raised homocysteine and scarce methionine levels are held accountable to precipitate the kidney pathology. Furthermore, Imerslund-Grasbeck syndrome, caused by proximal cobalamin pathway defects in CUBN and AMN, is leading to a malabsorption of cobalamin from the gut due to a deficiency of the cubam receptor failing to take up the complex of cobalamin and the intrinsic factor. From a kidney standpoint, these patients suffer from a persistent nonprogressive proteinuria