This might open a can of worms... My dog breed is subject to a condition called cerebellar ataxia. In the last ten years or so, much data has been collected, and a test for a responsible gene devised. I was close to one of the first dogs studied to develop this research, and used homeopathy to attempt to relieve his symptoms. It seems, however, that this quickly becomes a physical issue unreachable by energetic means.
The question is about the relationship of miasmatic influences to genetic disorders. I have always felt that chronic disease, of course, can be inherited, but that expression of it in a given individual depends on that subject's particular strengths and weaknesses, and upon the combination of chronic factors inherited as well as the proximal insults which generate their own damage.
At some point, physical changes due to unaddressed chronic disease become genetically transmittable, and, as part of physiology they are relatively inaccessible by homeopathic treatment. If such changes create symptoms, though, the symptoms may still be accessible, such as inflammation from structural issues, or chronically poor organic or glandular function.
I think it's always worth a try, however, to treat for the "impossible", like dealing with mental symptoms, or growing new hip sockets, or regenerating the myelin sheath of the nerves. The body STILL works in mysterious ways, and we need to keep that belief in the backs of our minds.