Adult Progressive Myoclonic Epilepsy

Has anyone been told by their epileptologist they have PME although genetic testing is negative ? Our son is 29 and has multiple forms of epilepsy starting at age 9 ( possibly was having at age 2 but undiagnosed according to doctors) , developed myoclonic epilepsy at age 12 and has progressed In severity and frequency since . He was born with some mental struggles in development as well as small and slow growth but he is now 5’8” but only weighs 92 pounds and had mentally gotten to a near age appropriate mental capacity until he turned 15 and suffered brain damage while hospitalized for EEG study and went into a severe gran mal and we were told he flatlined for a minute or two but his brain had been without oxygen too long and was temporarily paralyzed in the left side for a few months but regained movement eventually . He was a ball player and a nuisance to his big brothers until the age of 19 when he woke up and went to get out of bed and had lost the use of his legs for no apparent reason or injury. He has been confined to a wheelchair since ( now confined to bed) and two years ago went status epilepticus and when he woke on the 8th day he could walk and talk for two weeks. We had started physical therapy again and been referred to an epileptologist who said it could be what is referred to as a “brain reset” but unfortunately this wasn’t the case. Physical therapist stopped his sessions on the 3rd week due to being so out of control with his Myoclonics that it was unsafe to continue and he had already become bedridden this same week. Doctors tested for PME but all test are negative , muscle and nerve test are perfect, MRI normal and EEG of course showed multiple epilepsies as well as the myoclonic activity. In their words he is the healthiest sick person they’ve seen. We have had all types of blood work done as well as having our home tested for any leads , toxins or poisons but all normal . I also asked if it could be an allergy to any of my cleaning products or any foods but all cane back fine. The doctors have said the prognosis is grim but have no diagnosis other than epilepsy so we are being referred to Mayo for another opinion but our son can’t even travel 3 states away . Has anyone ever experienced this type of issue on any level ? We do have multiple epileptics on both sides but all test came back as no familial abnormality found. He had his first VNS ( 5th replacement just done) implanted at the same time he lost use of his legs but had also started Keppra 2000 mg on top of his Clonazepam, Lamictal, Zonisamide, and Epidiolex with no control at all and worsening each day. Any information is appreciative but we are running out of time as he is now showing dementia like moments at a higher occurrence along with speech impairment, more choking episodes with food or drink and is looking at possibility of requiring feeding tube. I apologize for the long read but we are desperate for advice .