Companion X dominant disease is also known as X companion dominant disease, this disease is caused by the dominant causative agent located on the X chromosome, its characteristics are as follows: 1, regardless of men and women, as long as the existence of the causative gene will be onset of the disease, but because of the female has two X chromosomes, so the incidence of females is about twice as high as that of males. 2, the patient’s parents must be a person suffering from the same disease, except for the gene mutation. 3, it can be inherited for several generations. The disease can be inherited for several generations, but the normal woman of the patient will not have the fatal gene re-transmitted to her offspring.4. Male patients can pass the disease to their daughters and not to their sons, and female patients pass the disease to half of their sons and daughters.The accompanying X-chromosome dominantly inherited diseases include anti-vitamin D rickets, hereditary chronic nephritis, and so on.