Crigler-Najjar syndrome

A 5-month-old female is brought to the pediatrician for evaluation of jaundice that began after a viral upper respiratory tract infection. She was born at 39 weeks gestation to a 27-year-old, gravida 1 para 1, woman via spontaneous vaginal delivery. The patient has been meeting developmental milestones. Family history is noncontributory. Physical examination shows scleral icterus and diffuse jaundice. Abdominal and neurological exams are unremarkable. Blood testing is performed and reveals the following:  

Laboratory value	Result
Hemoglobin	13.9 mg.dL
Leukocyte count	6,800/mm3
Total bilirubin	12.7 mg/dL
Conjugated bilirubin	0.3 mg/dL
Alanine  aminotransferase	15 U/L
Aspartate  aminotransferase	16 U/L

Phenobarbital is administered, and repeat total serum bilirubin is measured at 7 mg/dL. Which of the following best describes the cause of this patient’s condition?