Rare disorders & disability entitlements help please

My husband is in the process of being diagnosed with a rare neuromuscular disorder. His neurologist has narrowed it down to 2 possible genetic disorders. His bloods have been sent to a genetic research team in london & could take up to 12 months to come back with a diagnosis. As it stands he may be the only person in the country with these disorders according to his specialist. He is currently receiving illness benefit but has to go see an independent doctor for the social welfare dept to assess him. I'm wondering what the doctor will be looking for as its not an everyday illness so how can he be assessed? He is applying for disability benefit but the form needs a diagnosis & it could be a year before his genetic tests come back so does he need to wait for those results or can he apply without? Our lives have been turned upside down with my husband being sick & unlikely to be able to work again so any information would be very helpful as stress exasperates his symptoms due to the effect of cortisol on his body. I have also emailed the muscular dystrophy assoc of Ireland but haven't gotten a reply yet so any other organizations that would deal with genetic neuromuscular disorders would be helpful. Thanks