If you and your brother have same symptoms then you can go for a genetic teating to confirm the disease or otherwise. If you see a good neuromuscular expert, they can tell you by clinically examining (if you are symptomatic) whether you are having the same pattern of muscle weakness as your brother. But the gold standard is genetic testing.
At present there are no definite therapies for nonakas myopathy.
Next Steps
Get a genetic testing done if you also have symptoms..