CBLC and hyperhomocysteinemia: Patients with cblC, cblD, and cblF defects are classified as having MMA combined with homocysteinemia (Fowler et al., 2008; Wang et al., 2010) accounting for 60–80% of cases in China (Wu et al., 2019), and cblC defects are the most common subtype (Carrillo-Carrasco et al., 2012).