Genetic testing alone is not adequate to make the diagnosis of a neuromuscular disorder. A complete work-up needs to be done which includes a muscle biopsy, CPK and complete physical examination.
I have had two parents contact me recently about the diagnosis of muscular dystrophy given their children when only genetic tests were done. Both of the physicians who made the diagnosis were geneticists, who apparently had not had neuromuscular training. When the doctors were asked about doing muscle biopsies they both said "No". My guess is that they did not have the training to do these and probably did not have labs where the muscle tissue could be processed.
No diagnosis of a potentially fatal disorder or any other disorder should be made just in a genetics lab. A great deal can go wrong, including human error or lab equipment problems. Fortunately, one of the mothers agreed to take her child to Mayo Clinic, the only place I will send neuromuscular patients in the U.S. I have not heard from the other parent, but am afraid she is not willing to challenge the doctor, even though it is not because of the expense involved in making the trip to Mayo Clinic. Yes, we have many more genetic tests than we did in the past, but a complete physical examination, the blood test, CPK, and a muscle biopsy are still necessary before a specific diagnosis should ever be made when there is muscle weakness and signs of a neuromuscular disorder.