Hello, I understand your concern because it is a little bit difficult to understand exactly from which diagnose some symptoms come. Well at first to know, it is that they both are autoimmune disease, that means that your body attacks his cells ( create antibody anti some specific cell in the organism). And the diagnose it is confirm from these antibodies, in this case they are called autoantibodies. Antisynthetase has antibody anti Aminoacyl-tRNA synthase ( a enzyme), and sclerodermia, depending of what kind of, has different antibodies. Both of these disease have some symptoms that can overlapping, or the same, because they both touch lungs and fingers like Reynaud phenomen. But just to remember, sclerodermia attacks the skin first ( so symptoms which are correlated with skin as : redness, swelling, tenderness, itching are due to this) and another thing to remember in sklerodermia it is that usually touch the skin of face, neck fingers and foot. Symptoms that are more specific for antisynthtase they are correlate with muscles( weakness) but also you can have arthritis. As they both are autoimmune disease, both of them cause fatigues and weight loss. I hope that my answer is helpful to you! Best regards! Dr Eniola