NF1 and plexiform neurofibroma: While ATRX is an X-linked tumor suppressor, our data support the notion that it is a cooperating mutation in both NF1-associated MPNSTs as well as sporadic MPNSTs, rather than an initiating mutation in tumorigenesis, as our data show a much higher percentage of MPNSTs have aberrant expression by IHC versus the precursor plexiform neurofibromas.