CBLC and Cognitive impairment: The levels of methylmalonic acid in serum total exosomes (Figure 3D) and in serum neuro-exosomes (Figure 3E) showed better performance than serum homocysteine (Figure 3A), methylmalonic acid in the urine (Figure 3B) and in the serum (Figure 3C) for distinguishing cblC-MMA patients with or without cognitive impairment.