Engineered retrovirii also have great potential for curing genetic diseases, and possibly other viral diseases. Their most important property is that they insert their genetic material into the host genome, where it will remain forever. All descendents of this cell will also contain the same genes. For example, a custom retrovirus could contain a special gene for insulin, and only infect cells in the pancreas that normally secrete insulin. They could then insert a functional copy of the insulin gene into the genome, and the cell would begin producing insulin. This would cure a few types of diabetes (in theory)