A number of theories have been proposed to explain the origins and pathogenesis of IH: placenta, metastatic, progenitor cell (a hemangioma-derived multipotential stem cell, based on expression of the stem cell marker CD133), extrinsic factor (hypoxic environment), neural crest/pericyte stem cell theory (pericyte-like stem cell tumors derived from neural crest, capable of adipocyte differentiation), and metastatic niche theory5. The gene discussed is PROM1; the disease is isolated hemihyperplasia.