LAUSR

Peripheral capillary oxygen saturation (SpO2), or pulse oximetry, is commonly used in modern medical practice as a basic vital index of health. Although low SpO2 is generally caused by pulmonary, cardiac, or vascular disease, hemoglobin (Hb) abnormalities can also cause reduced pulse oximetry. Hb alterations, however, are sometimes overlooked as the cause of low SpO2, especially when they are congenital. Hemoglobin Seattle (Hb-Seattle) is an inheritable hemoglobinopathy that involves the substitution of aspartic acid for alanine at codon 70 of the b-globin chain, a side chain of which is located in the heme contact region of the protein. Because mutations in this region could affect molecular stabilization and oxygen affinity, patients with this variant have hemolytic chronic anemia and hypoxia symptoms. Since it was first identified in 1970, Hb-Seattle has been reported in three families, with a total of nine individuals reported to date (Table S1). We herein describe the first reported case of Hb-Seattle in Japan, the diagnosis of which was prompted by low SpO2. A 13-year-old Japanese girl was referred to Saitama Citizens Medical Center because of normocytic anemia and low SpO2. She was incidentally diagnosed with anemia at the age of 12 at a local clinic. The parent reported that the patient had displayed facial pallor intermittently since early childhood. Her father, who had died of renal cancer, had a history of pediatric anemia of undetermined etiology persisting into adulthood. The patient was ethnically pure Japanese and had no other family history of hematological disease. Although she was otherwise in good health on admission, the patient had facial pallor with anemic palpebral conjunctiva. Although SpO2 was 89%, no intolerance to physical exercise was observed. No jaundice, hepatomegaly, or splenomegaly was observed. Laboratory test indicated normocytic normochromic anemia with hemolysis: Hb, 8.9 g/dL; mean corpuscular volume, 90.7 fL; reticulocyte count, 3.25%; serum haptoglobin, 8 mg/dL (reference range, 19–170 mg/dL); and fetal Hb (HbF), 2.7% (reference range, 0–1.7%). Congenital cyanotic heart disease and respiratory disease were ruled out based on imaging and physical examinations. Peripheral blood smear showed target cells (Fig. 1a) and inclusion bodies in red blood