Crigler‐Najjar Syndrome Type 1: Pathophysiology, Natural History, and Therapeutic Frontier

Background and Aims We describe the pathophysiology, treatment, and outcome of Crigler‐Najjar type 1 syndrome (CN1) in 28 UGT1A1 c.222C>A homozygotes followed for 520 aggregate patient‐years. Approach and Results Unbound (“free”) bilirubin (Bf) was measured in patient sera to characterize the binding of unconjugated bilirubin (BT) to albumin (A) and validate their molar concentration ratio (BT/A) as an index of neurological risk. Two custom phototherapy systems were constructed from affordable materials to provide high irradiance in the outpatient setting; light dose was titrated to keep BT/A at least 30% below intravascular BT binding capacity (i.e., BT/A = 1.0). Categorical clinical outcomes were ascertained by chart review, and a measure (Lf) was used to quantify liver fibrosis. Unbound bilirubin had a nonlinear relationship to BT (R2 = 0.71) and BT/A (R2 = 0.76), and Bf as a percentage of BT correlated inversely to the bilirubin–albumin equilibrium association binding constant (R2 = 0.69), which varied 10‐fold among individuals. In newborns with CN1, unconjugated bilirubin increased 4.3 ± 1.1 mg/dL per day. Four (14%) neonates developed kernicterus between days 14 and 45 postnatal days of life; peak BT ≥ 30 mg/dL and BT/A ≥ 1.0 mol:mol were equally predictive of perinatal brain injury (sensitivity 100%, specificity 93.3%, positive predictive value 88.0%), and starting phototherapy after age 13 days increased this risk 3.5‐fold. Consistent phototherapy with 33‐103 µW/cm2•nm for 9.2 ± 1.1 hours/day kept BT and BT/A within safe limits throughout childhood, but BT increased 0.46 mg/dL per year to reach dangerous concentrations by 18 years of age. Liver transplantation (n = 17) normalized BT and eliminated phototherapy dependence. Liver explants showed fibrosis ranging from mild to severe. Conclusion Seven decades after its discovery, CN1 remains a morbid and potentially fatal disorder.