MTHFD1 and hyperinsulinemic hypoglycemia, familial, 4: The notion that it takes two or more toxic metabolites to trouble endothelial cells is supported by the occasional occurrence of pseudo-TMA in nutritional B12 deficiency [45], which—like MMACHC and MTHFD1 deficiency—is characterized by combined hyperhomocysteinemia and methylmalonic acidemia and low methionine levels.