NCSTN and histiocytic sarcoma: The most widely reported genetic change occurring in familial HS is in the nicastrin-coding gene NCSTN (OMIM: # 142690 ACNE INVERSA, FAMILIAL, 1; ACNINV1) that encodes a 78 kDa type I single pass transmembrane protein, is highly glycosylated [49], and plays a crucial role in maintaining the stability of GSC and regulating intracellular protein trafficking [50].