Based on a message I received, it still seems that there is some confusion on FQ damage susceptibility and MTHFR Mutations. I received a message from a person who, evidently from what they read on 
Facebook, garnered that the MTHFR mutations are the reason for floxing and despite my attempts to enlighten them, they still did not accept it. There is a lot of misinformation floating around. MTHFR can be just one piece to the puzzle of FQ damage. According to Dr. Ben Lynch, probably the foremost expert on MTHFR mutations, the rate of one MTHFR mutation in the standard population is a whopping 50% and the likelihood of having 2 copies is between 10% and 20%. Those of Italian and Mexican ancestry can have a much larger rate of MTHFR mutations.
In most health issues where MTHFR is involved there are likely other issues at play. Personally I have seen genetic information on some severely affected FQ folks that do not have any MTHFR mutations. Some of these individuals got their genetics tested only to be disappointed when they did not have the MTHFR variation. I know many are desperate to find the one ‘smoking gun’ that explains floxing. What is more apropos is that it is likely that several paths can lead to similar symptomatology. This is not to say that there are not some similarities, genetic or otherwise. We all must remember that elements of floxing are as unique as our individual physiologies and treatments must be tailored to the person.
Actually people with neuromuscular diseases, like me are also more susceptible to fluoroquinolone toxicity.I think every person with neuromuscular disease will have serious side effects if he takes a quinolone. Even in some websites the relation between tendinitis and NMD is clearly stated. I m sure my dr never gave a second thought about this while prescribing. In many people neuromuscular diseases dont show any sympoms which makes the patient go to the dr and drs just dismiss the symptoms as normal. In my case i had weakness closing the mouth and more frequent choking due to aspiration while drinking water, nasal twang in voice due to weak palate muscles and very excessssive sweating and less stamina in sports no matter how hard i worked on improving my stamina. Then i took this avelox for sinus infection and then my world came down, was down for almost a year.
Thank you for your insight. I do agree with you that anyone with a neuromuscular disease should be overly cautious and do everything they can to avoid taking a quinolone. Mitochondrial dysfunction and susceptibility plays an important role. It is vitally important that we get a black box warning for mitochondrial toxicity on all quinolones.