Authors report clinical symptoms and the results of haematological and metabolic investigations in the girl with megaloblastic anaemia 1 (Imerslund-Gräsbeck). In the girl with normal development till the age of 3 years, severe transfusion dependent megaloblastic anaemia (Hb 44 - 60 g/l, MCV 103 - 120 fl), ataxia and progressive mental and motor deterioration developed. Her tongue had a smooth red atrophic mucous membrane and she had non-selective proteinuria (0.4 - 0.8 g/l). The bone marrow was hypercellular with dyserythropoetic changes, large metamyelocytes and hypersegmented neutrophiles. The level of serum vitamin B12 was low (B12 < 60 ng/l, normal level being > 180), the serum folate level was normal. Metabolic investigations revealed severe hyperhomocysteinaemia (P-homocystein 153.3 mol/l, controls < 10) and methylmalonic aciduria (U-MMA 499 mmol/mol creat., controls < 15). Low absorption of vitamin B12 was found using the Shilling test. Histochemical investigations of gastric biopsy revealed no mucous atrophy. After parenteral treatment with vitamin B12 the percentage of reticulocytes promptly increased from 6 to 237 per mille and subsequently all haematological and metabolic parameters of the disease normalised. The girl also improved clinically and now, at the age of 5.5 years, the girl is in very good clinical condition, only mild proteinuria persists.

        Key words: megaloblastic anemia, vitamin B12