2-year-old girl with pancytopenia due to vitamin B12 (cobalamin) deficiency.

Abstract

Case A 2-year-old girl of Mexican and Spanish descent came to our hospital with her mother for 2 weeks of pallor and fatigue. She was born full term to parents who were first cousins. Past medical history was unremarkable, and development was appropriate. Diet was balanced and unrestricted. Growth parameters were appropriate. She appeared well nourished but with obvious pallor. Liver and spleen were not palpable. Neurologic examination was unremarkable. Laboratory tests revealed pancytopenia with white blood cell count of 2.9 × 10 3 /μL, haemoglobin of 4.8 g/dL, platelets of 98 × 10 3 /μL, mean corpuscular volume of 94 fL and red cell distribution width of 43%. Additional serum tests showed lactate dehydrogenase of 3128 U/L (normal 90‐220), total bilirubin 1.2 mg/dL (normal 0‐1) and direct bilirubin 0.3 mg/dL (normal 0‐0.3). On review of the peripheral blood smear, macrocytosis and hypersegmented neutrophils were seen. The differential diagnosis of macrocytosis in infants and children is shown in Table 1. The finding of megaloblastic anaemia, defined by hypersegmented neutrophils in the peripheral blood, raised concern for a problem with deoxyribonucleic acid (DNA) synthesis during red blood cell production. Therefore, serum levels of vitamin B12 (cobalamin) and folate were obtained. Vitamin B12 was 45 pg/mL (normal 211‐911), and folate was 14 ng/mL. Urine dipstick showed 30 mg/dL protein. DNA mutation analysis revealed a homozygous mutation of the amnionless gene (AMN) consistent with ImerslundGrasbeck syndrome (IGS, megaloblastic anaemia 1; OMIM #261100). Our patient was treated with intramuscular vitamin B12 injections. At a clinic visit 2 months later, serum vitamin B12 level was 384 pg/mL. The patient is now a healthy and thriving 6-year-old girl. She continues to have mild proteinuria (30‐ 100 mg/dL) without evidence of impaired glomerular function.