Two copies causes Phenylketonuria. But there is zero chance that you're learning about your own Phenylketonuria from a Promethease report. Unless Phenylketonuria is detected at birth and a strict phenylalanine-restricted diet is followed, severe medical problems would have occurred.
It is more likely that you've been affected by this being an ambiguous flip but something about your data is behaving differently than from most other users. firstname.lastname@example.org would like to hear from you so that we can understand and resolve this source of confusion.