Penicillin is the classic antibiotic, a frontline resistance to many bacterial infections. Unfortunately, penicillin is reportedly the cause of many allergic reactions. Researchers have found a genetic linkage to the penicillin allergy that is creating a higher risk of predisposition to this allergic effect. The gene associated with this allergy is a variation to a gene complex on an immune system gene. The gene complex that is affected is called the histocompatibility complex gene HLA-B. This gene complex was already known to have linkage with bad responses to other drugs, including some HIV medication and allergic reaction to gout medication. In order to identify this gene as the source, researchers looked over 600,000 peoples electronic health records and utilized several genetic tools to identify similarities in the sample. Ultimately, they found that a specific "hot spot" on chromosome 6 was a constant, and this region held a variation of the HLA-B gene identified as HLA-B*55:01. Comparing there findings to over 1 million European samples through the use of the genetic testing site, 23 and me, they found the same genetic link of the HLA-B gene complex. Researchers say there is still a lot more evidence to come to light to fully understand the genetic linkage to penicillin allergy, but this is a good start.