The proband (A.II.1, male, 16 years old, Supplemental Figure 1A; supplemental material available online with this article; https://doi.org/10.1172/JCI193099DS1) and his younger brother (A.II.2, male, 8 years old) both presented with prolonged, transient neonatal unconjugated hyperbilirubinemia followed by persistently elevated transaminases, serum creatine kinase, and myoglobin levels since 6 months and 12 months of age, respectively. Here, MB is linked to Hyperbilirubinemia.