A320 FLT CREW ENCOUNTERS SEVERE TURB AND LOSES ALT.

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IN CRUISE FLT; 80 MI SSE OF ZZZ1; I AM PF. WE STARTED TO EXPERIENCE LIGHT CHOP AND BEGAN TO FLY THROUGH HIGH THIN CLOUDS. I TURNED ON THE SEATBELT SIGN. I CONTACTED ATC AND ASKED ABOUT TURB. THE CTLR RESPONDED THAT WE WERE GOING AROUND THE SOUTHERN EDGE OF A SQUALL LINE AND WE SHOULD BE CLR OF TURB IN ABOUT 40 MI. OUR RADAR WAS CLR. HE HAD NO PLT RPTS OF TURB IN THE AREA. I THEN SLOWED THE ACFT TO .76 MACH AND MADE A PAX ANNOUNCEMENT THAT WE WERE FLYING OVER THE TOP OF AN AREA OF RAIN AND SHOULD EXPECT SOME TURB AND TO ASSURE THEY WERE SEATED WITH THEIR SEATBELT FASTENED. I THEN RECEIVED A CALL FROM OUR 'A' FLT ATTENDANT ASKING ABOUT TURB AND TOLD HER THAT IT SHOULD LAST ABOUT 10 MINS OR SO. AT THIS POINT TURB BEGAN TO INCREASE. WE ALSO ENTERED CLOUD TOPS. I TOLD HER EVERYONE SHOULD BE SEATED. SHORTLY AFTER THAT WE ENTERED THE AREA OF SEVERE TURB. WE WERE NOT ABLE TO HOLD ALT AND AIRSPD DROPPED QUICKLY. THE AUTOPLT DISCONNECTED (ON ITS OWN) AND I BEGAN TO HAND FLY THE ACFT. I BEGAN TO DSND BECAUSE WE BEGAN TO FEEL AN IMPENDING STALL. I TRIED TO FLY THE FLT DIRECTOR COMMANDS TO THE BEST OF MY ABILITY. THE CAPT CALLED ZZZ AND 'DECLARED AN EMER' SINCE WE WERE UNABLE TO HOLD ALT. WE LOST ABOUT 4000 FT IN ABOUT 40 SECONDS AND SHORTLY THEREAFTER WE WERE IN THE CLR. WE THEN LEVELED OFF AT FL320 AND RECEIVED CLRNC FROM ZZZ TO REMAIN AT FL320 AND TURN L 20 DEGS.