A form of methylmalonic acidemia with homocystinuria, an inborn error of vitamin B12 (cobalamin) metabolism characterized by megaloblastic anemia, lethargy, failure to thrive, developmental delay, intellectual deficit and seizures. The disorder is caused by mutations in the LMBRD1 gene (6q13) and is transmitted in an autosomal recessive manner. The disease is Monarch Disease Ontology identifier MONDO_0010183 (methylmalonic aciduria and homocystinuria type cblF). Also known as: cblF defect, cobalamin F defect, cobalamin F deficiency, combined defect in adenosylcobalamin and methylcobalamin synthesis, type cblF, inherited methylmalonic acidemia and homocystinuria, lysosomal membrane cobalamin transporter deficiency, methylmalonic aciduria with homocystinuria, type cblF.