Imerslund-Gräsbeck syndrome (IGS) is a rare autosomal recessive disorder caused by pathogenic variants in CUBN or AMN genes, leading to selective vitamin B12 malabsorption. Symptoms include failure to thrive, cytopenia, and proteinuria. This study aims to analyze clinical, biochemical, and molecular genetic profiles of 4 patients diagnosed with IGS at a single center in Argentina. Macrocytic anemia and neutropenia were present in three cases, two with thrombocytopenia. All had proteinuria. A novel CUBN: c.2450G>A; p.(Cys817Tyr) variant was found in three patients, while the fourth carried AMN: c.1006+34_1007-31del in homozygous state. Early and lifelong parenteral vitamin B12 ensures an excellent prognosis.