All our characteristics are programmed at the moment of conception, not at birth!

Also, the normal movement of the heavenly bodies has meant that all the constellations are now a whole 'sign' out since the system was set up in ancient Babylon, so you may find astrology not too reliable a guide here.
Perhaps a more relevant question would be: How many other scanners/gifted people are there in your natural family (so excluding in-laws)?