homocystinuria (disease) autosomal recessive disease homocystinuria without methylmalonic aciduria Homocystinuria without methylmalonic aciduria is an inborn error of vitamin B12 (cobalamin) metabolism characterized by megaloblastic anemia, encephalopathy and, sometimes, developmental delay, and associated with homocystinuria and hyperhomocysteinemia. There are three types of homocystinuria without methylmalonic aciduria; cblE, cblG and cblD-variant 1 (cblDv1). ICD10:E72.1 MONDO:0018964 Orphanet:622 SCTID:721225009 UMLS:C4303479 functional methionine synthase deficiency homocystinuria without methylmalonic aciduria methylcobalamin deficiency neurometabolic disease cerebral organic aciduria inborn disorder of cobalamin metabolism and transport constitutional megaloblastic anemia due to vitamin B12 metabolism disorder