HBD

HBD (unknown acronym meaning) is a disease from the MegaMan Battle Network series. Two known cases of it are revealed by the series: Hub Hikari and Mamoru. The first case "died", and the latter survived thanks to advanced technology. Symptoms include severe chest pain, and being unable to breathe. It is so rare, the only place they could've tested Mamoru for HBD was at Seaside Hospital. There are no curing medications as a bacterium or virus could not have caused Mamoru or Hub Hikari to have such severe chest pain; it is likely a hereditary disease/disorder. The only treatment and possible cure is surgery, but the procedures name is never revealed.

Trivia

 * HBD in real life is in fact short for Hemoglobin subunit delta, a protein that in humans is encoded by the HBD gene.
 * The meaning of "HBD" was never revealed, but there are speculations that HBD stands for "Heart Beat Disorder".