b able " ▁diagn osis ▁is ▁made ▁when ▁no ▁gen etic ▁diagn osis ▁can ▁be ▁made , ▁but ▁the ▁patient ▁has ▁all ▁other ▁characteristics ▁of ▁a ▁particular ▁disease ; ▁the ▁chance ▁of ▁the ▁same ▁diagn osis ▁being ▁made ▁ 2 0 ▁years ▁later ▁is ▁estimated ▁to ▁be ▁ 8 5 - 9 7 %. ▁Finally , ▁a ▁" possible " ▁diagn osis ▁is ▁made ▁when ▁the ▁patient ▁has ▁only ▁some ▁of ▁the ▁characteristics ▁of ▁a ▁disease ▁which ▁are ▁present , ▁but ▁not ▁all . ▁ ▁Class ifications ▁ ▁There ▁are ▁many ▁forms ▁of ▁P ID . ▁The ▁International ▁Union ▁of ▁Im mun ological ▁Soci eties ▁recogn izes ▁nine ▁classes ▁of ▁primary ▁imm un ode fic ien cies , ▁total ing ▁over ▁ 1 2 0 ▁conditions . ▁A ▁ 2 0 1 4 ▁update ▁of ▁the ▁classification ▁guide ▁added ▁a ▁ 9 th ▁category ▁and ▁added ▁ 3 0 ▁new ▁gene ▁defect s ▁from ▁the ▁prior ▁ 2 0 0 9 ▁version . ▁, ▁there ▁are ▁approximately ▁ 4 3 0 ▁forms ▁of ▁P ID ▁that ▁have ▁been ▁identified . ▁ ▁D ifferent ▁forms ▁of ▁P ID ▁have ▁different ▁mechan isms . ▁R ough ▁categor izations ▁of ▁conditions ▁divide ▁them ▁into ▁hum oral ▁imm unity ▁dis orders , ▁T - cell ▁and ▁B - cell ▁dis orders , ▁ph ag oc yt ic ▁dis orders , ▁and ▁complement ▁dis orders . ▁ ▁Most ▁forms ▁of ▁P ID ▁are ▁very ▁rare . ▁Ig A ▁def ic iency ▁is ▁an ▁exception , ▁and ▁is ▁present