Expression of ARNT and GDI2 in human medulloblastoma subgroups. Box plots showing relative expression of ARNT ( A , B ) and GDI2 ( D , E ) in normal cerebella (CB; fetal n = 9, adult n = 5) and medulloblastoma samples from the MAGIC consortium profiled on Affymetrix exon arrays. The 103 medulloblastomas in the discovery set ( A , D ) and the 285 in a nonoverlapping validation set ( B , E ) were classified according to molecular subtype (WNT, SHH, Group 3, Group 4). Log2 expression is a measure of the luminosity of the gene probe signal, corrected for the background luminosity of each array and normalized using control probes across different arrays. C, Bar graph correlating M-stage with ARNT mRNA level (high = top quartile; low = bottom quartile) in Group 4 medulloblastomas (n = 200).