Background: Imerslund-Gräsbeck syndrome is an rare autosomal recessive disorder of vitamin B₁₂ malabsorption. Here, we report a rare case of a second child in the same family with Imerslund-Gräsbeck syndrome presenting with chronic constipation, an unusual presentation of the disease. Case presentation: A 2 years and 4 months old girl, the second-born child of nonconsanguineousparents, presented with chronic constipation for 6 months. She had shown a suboptimal response to regular laxatives. She had a significant family history , with her elder brother being diagnosed with Imerslund–Gräsbeck syndrome at 4 years of age when hepresented with lower limb weakness and anaemia. The physical examination was normal except for pallor. Her haemoglobin was 7 .8g/dL, and the blood picture showed evidence of vitamin B12 deficiency . Her serum vitamin B12 level (87pg/mL) was low , and plasma homocysteine level was high (60? mol/L), confirming vitamin B12 deficiency . Urine albumin: creatinine ratio was high (15.7mg/mmol). Based on the positive family history and laboratory evidence of vitamin B12 deficiency and proteinuria, the diagnosis of Imerslund-Gräsbeck syndrome was made. She was commenced on intramuscular hydroxocobalamin and oral folic acid. She showed significant clinical improvement in constipation, haemoglobin increased to 10.9g/dL, and serum vitamin B₁₂ levels normalised (1604 pg/mL) after 2 weeks of treatment. Conclusions: We report a second child with Imerslund-Gräsbeck syndrome, a rare genetic cause of vitamin B12 deficiency from the same family . This report describes an unusual presentation of the disease as chronic constipation and highlights the importance of family screening of rare genetic disorders.