Many patients ask the question: I am the only patient in my family for several generations, and my parents are healthy, so why is my disease genetic? There are several modes of inheritance in humans. These include autosomal dominant, autosomal recessive, X-dominant, X-recessive, and mitochondrial inheritance. Moreover, today, after decades of family planning, many families have only 1 child, and genetic diseases in the form of epidemics are more common. Autosomal dominant inheritance is not related to the birth of a male child. If one of the parents is sick, the probability of the child getting the disease is 50%, and in case of a large family, there are basically sick people from generation to generation. However, if the gene that causes the disease is incompletely episodic, meaning that some people carry the mutated gene but do not develop the disease, such as in PKD (seizure-triggered dystonia), which is a typical example, and DRD (dopa-responsive dystonia), which is also common. One of the parents carries the mutation but does not develop the disease, but it is passed on to the child, who develops the disease, manifesting as epidemic, or some of the siblings have the disease. Autosomal recessive inheritance is also not associated with the birth of male children. However, unlike dominant inheritance, where both parents are normal, but each parent carries a mutation, and the parents pass both mutations to the child, the child will develop the disease, whereas if only one mutation is passed, the child will not develop the disease. In this type of inheritance, special care should be taken not to marry inbred. X-linked inheritance, on the other hand, is related to gender. X-linked inheritance is more common in the X-recessive mode, where the boy gets the disease and the girl does not. The most common examples are DMD and BMD, two types of myotonic dystrophy. In families, the disease often manifests itself as a grandfather or uncle having the disease and a grandson or nephew having the disease. While the mother and grandmother of the child are normal and the father is normal. There is also a special type of inheritance, mitochondrial inheritance, which is a matrilineal inheritance, regardless of the boy or girl, the mitochondrial genes come from the mother (many studies have shown that the child’s intelligence depends on the mother’s intelligence, which makes sense from this point of view), but the most important thing to look at is the proportion of mitochondria with mutations to all mitochondria, not to say that as long as there are mutations will get the disease, but It does not mean that if there is a mutation, the disease will occur, but the number of mutations has to reach the level of pathogenicity. There is also a case where both parents are normal, but during pregnancy, the child’s genes mutate on their own, that is, the newborn mutation, but this mutation can cause disease if it is passed on to the next generation. After all, every genetic disease has a first ancestor from whom the mutation starts, and we call the first person who produces the mutation the “founder”, and the mutation is passed down from him to the next generation. This is just a brief introduction to the way of inheritance. I would like to tell you that even if the whole family has been normal for many generations and there is only one patient, he/she may still have some kind of genetic disease. For eugenics, you can consult your doctor about the specifics of each disease, what kind of situation you can have a child directly without prenatal diagnosis, and what kind of situation you must have prenatal diagnosis in order to avoid passing the disease to the next generation!