Recognized causes are Chemicals (eg, benzene, inorganic arsenic) Medications (eg, antineoplastic drugs, antibiotics, nonsteroidal anti-inflammatory drugs, antiseizure medications, acetazolamide, gold salts, penicillamine, quinacrine) or toxins Hepatitis (seronegative for hepatitis viruses) Pregnancy Radiation Viruses (Epstein-Barr virus and cytomegalovirus) Inherited disorders of bone marrow failure due to genetic mutations (eg, Fanconi anemia, Shwachman-Diamond syndrome, dyskeratosis congenita) The precise mechanism remains unclear, but in the majority of acquired cases, the mechanism involves an immune attack on the hematopoietic stem cell.