In addition to the “loss expression” due to the complete genetic inactivation of the SWI/SNF complex subunits, a pattern of partial expression or “mosaic expression” has been recognized in conditions such as schwannomatosis and tumors such as gastrointestinal stromal tumor (GIST) and ossifying fibromyxoid tumor [29,30]. The gene discussed is SMARCA1; the disease is gastrointestinal stromal tumor.