Case Report: Imerslund Grasbeck syndrome: a rare cause of megaloblastic anemia in a well-nourished child

Megaloblastic anemia, characterized by macrocytic anemia, is most commonly caused by nutritional vitamin B12 deficiency; however, inherited disorders of cobalamin absorption should be considered in children with adequate dietary intake. One such disorder is Imerslund–Gräsbeck syndrome (IGS), a rare autosomal recessive condition characterized by selective intestinal malabsorption of vitamin B12 due to mutations in the CUBN or AMN genes. We report a 7-year-old boy, born of a third-degree consanguineous marriage, who presented with generalized rash, easy fatigability, and recurrent oral ulceration. Examination revealed pallor and hyperpigmented knuckles without organomegaly. Growth parameters were between the 10th and 25th centiles. Investigations showed severe macrocytic anemia (hemoglobin 2.5 g/dL), leukopenia, thrombocytopenia, markedly reduced vitamin B12 levels (<50 pg./mL), and peripheral smear findings of macrocytosis with hypersegmented neutrophils. In view of adequate nutritional intake, further evaluation for malabsorption was undertaken. There was no clinical evidence of gastrointestinal malabsorption, and anti-intrinsic factor antibody testing was negative. Urinalysis demonstrated mild proteinuria. Genetic analysis identified a homozygous mutation in the AMN gene, confirming the diagnosis of IGS. The child started on parenteral vitamin B12 therapy with plans for lifelong supplementation at intervals guided by clinical response. IGS should be suspected in children with megaloblastic anemia despite adequate dietary intake, particularly in the presence of proteinuria, parental consanguinity, or a poor response to oral supplementation. Early diagnosis and timely initiation of lifelong vitamin B12 therapy are essential to ensure optimal hematological recovery, growth, and neurodevelopmental outcomes.