This is an investigational study. Methionine restriction diet (Hominex®-2 Amino Acid-Modified Medical Food) has been approved by the FDA for nutrition support of children and adults with vitamin B6-nonresponsive homocystinuria. However, its use in this study is investigational. Temozolomide has been approved by the FDA for the treatment of brain tumors and is commercially available. The use of this combination is experimental. Forty-four participants will take part in this study.