AGRICULTURE, ARE DUBBED THE PARKINSON'S BELT. >> Reporter: ACROSS THE COUNTRY, BOXING CLASSES ARE PACKED. >> I COME ALMOST EVERY SINGLE DAY. SOMETIMES TWICE A DAY. IN A FITNESS CLASS NOBODY HOPES TO HAFTED JOINT FOR PEOPLE LIVING WITH PARKINSON'S. SELECT THE WORD GOT OUT ABOUT WHAT WE WERE DOING. WE HAD HUNDREDS OF FIGHTERS. IN IT CAUSES TREMORS AND MUSCLE STIFFNESS. MANY PATIENTS AND A IN WHEELCHAIRS. THE FASTEST GROWING NEUROLOGICAL DISEASE IN THE WORLD. 90,000 AMERICANS WILL RECEIVE A DIAGNOSIS THIS YEAR. NEARLY 1 MILLION ARE LIVING WITH IT. >> I WAS TOLD IT IS SLOW-MOVING BUT IT WILL NOT GO AWAY. >> Reporter: CHILDREN CLOSE TO THE FACTORIES PLAYED IN A CLOUD OF SMOG AND COAL DUST. WE HAD NO IDEA WHAT IT WAS. WE WERE JUST HAVING FUN. IN THOSE CHILDREN ARE SENIOR CITIZENS AND MANY HAVE PARKINSON'S. THIS AREA IS A HOTSPOT ACCORDING TO A STUDY. THE NUMBER OF PEOPLE WITH PARKINSON'S IS THE HIGHEST IN THE COUNTRY. SOME PLACES MORE THAN QUADRUPLED THE NATIONAL AVERAGE. SOME SCIENTISTS ARE CALLING IT THE PARKINSON'S BELT. REGIONS IN THE U.S. WITH HIGH RATES OF THE DISEASE. WHY PEOPLE GET IT IS A BIG MYSTERY. REDHEADS COULD BE MORE LIKELY TO GET IT WHILE OTHERS SHOW THAT SMOKERS ARE LESS SO. RESEARCHERS DON'T KNOW WHY BUT THEY THINK ENVIRONMENTAL FACTORS PLAY A BIG ROLE IN WHO GETS IT. WHICH AND HOW MUCH, AND STILL IS UNCLEAR. >> IF IT WAS DUE TO CHANCE, YOU WOULD NOT EXPECT TO SEE PARTS OF THE COUNTRY TO HAVE HIGHER RATES THAN OTHER PARTS. IN A PROFESSOR OF NEUROLOGY. HE BELIEVES CHEMICALS USED IN MANUFACTURING AND AGRICULTURE TRIGGER THE DISEASE. EVEN IF THE FACTORIES AND FARMS ARE LONG GONE. >> HIGH LEVELS OF POLLUTION AND CONTAMINATED WITH A CHEMICAL USE FOR DRY-CLEANING. >> Reporter: THE EPA HAS PROPOSED A RULE TO BAN IT. IN PICTURE, UNDERTAKEN RESEARCH TO THE FACTORS THOUGHT TO CONTRIBUTE. >> WHAT EVERYBODY IS WORKING ON, TRYING TO FIND OUT WHAT IS CAUSING THE DISEASE? >> Reporter: HE HAS INTIMATE KNOWLEDGE OF SYMPTOMS. HE WAS DIAGNOSED IN 2021. HE WAS RESEARCHING A CHEMICAL USED IN THE SIDES -- PESTICIDES. >> I WAS CARELESS AND EXPOSED MYSELF IN ODD WAYS. -- BAD WAYS. MY GUESS IS THAT MAKING A MODEL PARKINSON'S DISEASE LED TO ME GETTING IT. >> Reporter: IN CALIFORNIA, PARKINSON'S ALLEY. WIDELY USED PESTICIDES ARE LINKED TO PARKINSON'S. >> CLEAR-CUT SHOWING THE EXACT USE OF PESTICIDES FOR HOW MANY POUNDS PER ACRE. HOW MANY GOT TREATED WITH WHAT PESTICIDES AND THE SYMPTOMS OF PARKINSON'S. >> Reporter: GENETICS ACCOUNT FOR A QUARTER TO A THIRD OF THE REASON PEOPLE GET IT. >> 70% IS UNEXPLAINED AND PRESUMABLY ENVIRONMENTAL. >> Reporter: THE HOPE IS THAT LEARNING COULD HELP PREVENT AND TREAT IT. THERE IS NO CURE. DOCTORS HAVE BEEN MASKING THE SYMPTOMS FOR DECADES. IT DOES NOT TREAT OR STOP THE PROGRESS. EVENTUALLY THEY STOP WORKING. FOR NOW, EXERCISE IS KEY TO SLOW THE PROGRESSION OF THE DIAGNOSIS. >> I DO IT EVERY DAY. I DO NOT FEAR FOR MY SCHEDULE. I FEEL IT IS REALLY HELPFUL. >> YOU ARE NOT ALONE HERE. EVERYBODY HAS PARKINSON'S. IT HAS BECOME A