Can you tell me if a disease is genetic, does that mean that everyone with that disease is related?

No,it is from a gene: No, it means that the cause of the disease is from a gene. Sometimes, however, there are spontaneous mutations in the gene. Certain conditions, such as neurofibromatosis, have a very high spontaneous mutation rate, so there will be no family history of the disease prior to the affected patient. Because it is an autosomal dominant disease, any child will have a 50% chance of having the disease.