AbstractBackgroundImerslund-Gräsbeck syndrome is a rare genetic disease characterised by vitamin B12deficiency and proteinuria.Case presentationA 4-year old Sri Lankan boy presented with gradually worsening difficulty in walking for two weeks duration. He was previously diagnosed and managed as having non-transfusion-dependent α-thalassaemia based on the presence of hypochromic microcytic anaemia, haemoglobin H inclusion bodies in the blood film and compound heterozygous α-thalassaemia genotype with a gene deletion. However, his transfusion requirement increased over the past three months and he gradually lost his motor developmental milestones during two weeks before admission. The neurological examination revealed generalised hypotonia, exaggerated knee jerks and extensor plantar response. His complete blood count showed pancytopenia, and bone marrow biopsy revealed megaloblastic changes. Serum vitamin B12and red blood cell folate levels were low. MRI revealed sub-acute combined degeneration of the spinal cord with characteristic ‘inverted V sign’. Urine analysis showed non-nephrotic range proteinuria. The diagnosis of Imerslund-Gräsbeck syndrome was made due to the presence of non-nutritional vitamin B12deficiency and asymptomatic proteinuria. He showed a rapid haematological and neurological improvement to intramuscular hydroxocobalamin.ConclusionsThis case report presents a rare occurrence of severe vitamin B12deficiency due to Imerslund-Gräsbeck syndrome masked by co-existent α-thalassaemia, resulting in serious consequences. It highlights the need for a high index of suspicion in evaluating children with severe anaemia, especially in the presence of mixed pathologies.