Fibroblasts were generated from skin biopsies collected by K.A.R. and L.A.W. in patients previously described (28 (link)) and expanded by culturing in Dulbecco’s modified Eagle’s medium + 10% fetal bovine serum for 2 to 3 weeks. Two control lines, 162D and 165D, were from healthy siblings of NF1 patients. Line 13 was generated from fibroblast line GM00498 (Coriell). Fibroblast lines were reprogrammed with nonintegrative plasmids as previously described (37 (link)). Clonal colonies displaying iPSC morphology were manually selected and subsequently cultured on a Matrigel substrate (BD Biosciences) with mTeSR1 medium (Stem Cell Technologies). To determine pluripotency, teratomas were generated via three subcutaneous injections of 100,000 dissociated iPSCs in mTeSR1/30% Matrigel into nonobese diabetic mice/severe combined immunodeficient mice (Jackson Laboratory). After 2 to 3 months, tumors were surgically removed and sections were hematoxylin and eosin–stained by the Gladstone Histology Core at UCSF. All experiments were conducted with lines between passages 10 and 30.