Whether its due to hereditary, or some unknown source, you are by all means unable to perform any type of magic. You can still know and learn magic, but you will be unable to apply it in practice.
FLAW. This is a flaw feat. At your DM's discretion, you may take this feat at level 1. If you do, you may also gain a feat, or increase two of ability scores by +1 (or one by +2).