The cblC type chosen in this study accounted for 94.7% of Chinese MMA combined with homocystinuria (Liu et al., 2018) but not for the other four subtypes of the combined cobalamin metabolism (cblD, cblF, cblJ, and cblX) in our current assay (Yu et al., 2013; Richard et al., 2018). Here, CBLC is linked to homocystinuria.