Mutations in the CUBN locus are known to be the cause of Imerslund-Gräsbeck syndrome (OMIM #261100, Finnish type) which is a rare (the estimated prevalence is <6∶1,000,000) autosomal recessive disorder characterized by vitamin B12 deficiency commonly resulting in megaloblastic anemia, and also neurological damage and mild proteinuria [15]. The gene discussed is CUBN; the disease is Gräsbeck-Imerslund disease.