The World Health Organization (WHO) classifies medulloblastomas into four molecular subgroups based on genetic characteristics: wingless (WNT-)-activated, sonic hedgehog (SHH-)-activated and TP53 wildtype, SHH-activated and TP53 mutant, and non-WNT/non-SHH (formerly groups 3 and 4) [2]. The gene discussed is SHH; the disease is medulloblastoma.