Hereditary spherocytosis

A 6-year-old girl is brought to the clinic by her parent due to repeated episodes of jaundice, pallor, and fatigue for the last 8 months and new-onset abdominal pain for the last 3 days. She is at the 35th percentile for height and 20th percentile for weight. The parent reports no pregnancy or birth-related complications and states that the patient had been relatively healthy previously. The parent states that the girl’s biological father had been hospitalized with similar symptoms as a child and had abdominal surgery, but the details of the surgery are unknown. The patient’s temperature is 37°C (98.9°F), pulse is 90/min, respirations are 24/min, and blood pressure is 118/72 mmHg. Physical examination shows an ill-appearing pale child with scleral icterus and splenomegaly. Laboratory tests are obtained and the results are shown below. The patient most likely has a defect in which of the following?

Laboratory Value	Result
Hematologic
Leukocyte count	6,500/mm3
Platelet count	250,000/mm3
Hemoglobin	9.6 g/dL
Mean corpuscular volume (MCV)	84 fL
Mean corpuscular hemoglobin concentration (MCHC)	42 g/dL (normal 32-36 g/dL)
Red cell distribution width (RDW)	15%
Reticulocyte count	9.1%