Significant reactions that were secondary to elevated levels of methemoglobinemia did not occur during the use of HDDCT, as they have been noted to occur at methemoglobin levels that are greater than 30% with life threatening reactions reported at levels of 50% or greater (arrhythmias; altered mental status, delirium, seizures, coma; profound acidosis) [91]. The gene discussed is HBG2; the disease is methemoglobinemia.