Discrepancy between the FontStyle enumeration and the available FontStyles of the CheckBox.Text FontStyles

The FontStyle enumeration is comprised of: Bold, Italic, Regular, Strikeout and Underline. Notwithstanding, when selecting a FontStyle of a CheckBox.Text font, the only available FontStyles are: Regular, Italic, Bold and BoldItalic. 1. Why does this discrepancy exist? 2. How can I enumerate the four above mentioned CheckBox.Text FontStyles?