LMBRD1, also known as NESI (nuclear export signal-interacting protein, is a lysosomal membrane protein that is thought be involved in the transport and metabolism of cobalamin. LMBRD1 was initially identified as interacting with the large form of the hepatitis delta antigen and may be required for the nucleocytoplasmic shuttling of the hepatitis delta virus. Mutations in this gene are associated with the vitamin B12 metabolism disorder termed, homocystinuria-megaloblastic anemia complementation type F (cblF).