UGT1A1 and kernicterus: However, the regional specificity of BR toxicity can also be observed in the Gunn rat, a model of kernicterus due to a spontaneous mutation in the UGT1A1 gene (Watchko, 2006; Watchko and Tiribelli, 2013), indicating that UGT1A1 may be not the reason for the CNS injury topography.