Myotonic dystrophy is a hereditary muscle degenerative disease characterized by limb muscular atrophy and muscle weakness, which primarily affects locomotion. Most affect walking and upper limb activity. Many patients or family members do not understand, why several generations of family members are fine, how come I got myotonic dystrophy that? In fact, this is a very professional problem, not only involves the genetic disease inheritance mode, but also involves the genetic probability of the problem, I strive to explain clearly in brief language. 1, myotonic dystrophy is a genetic disease, according to the type of different will have different ways of inheritance, most of the X-linked recessive inheritance, autosomal dominant inheritance, autosomal recessive inheritance of these three ways. Pseudohypertrophic dystrophy is X-linked recessive and is a “male-to-female” type of disease, with males developing the disease and females carrying the gene. If a woman carries the gene, there is a 50% chance that the gene will be passed on to the next generation of boys, and a 50% chance that the gene will be carried by the next generation of women. This would explain the phenomenon that many families have both sick and normal males in the next generation. However, the patient may also have a new mutation in the gene and not carry the disease-causing gene in the family. 2, autosomal inheritance patients have no genetic history in the family, parents are not sick, the offspring of the disease for two reasons: first, the offspring of the disease-causing gene mutation is the patient’s personal gene mutation, not from the family inheritance; second, there is a disease-causing gene in the family, but it is a recessive inheritance, has not been revealed until the patient’s parents have carried the disease-causing gene, the patient was received by the disease-causing genes of the two parents, resulting in a pure combination of The incidence of the disease is 25%. Therefore, myotonic dystrophy is a genetic disease, not necessarily a family history, because there is a certain chance that genetic diseases will be passed on to the next generation. The lack of gene expression in the family that carries the causative gene and the new mutation of the gene are the main reasons why some patients with myotonic dystrophy do not have a family history.