X-linked inheritance patterns result from mutations located on the X chromosome. Females have two X chromosomes of which only one carries a mutation in X-linked dominant disorders. This usually results in expression of the disease and women with a single mutation have the disorder caused by the mutation. Half of their offspring, male and female, will inherit the mutation. Men, with only one X chromosome, will always have the condition if they inherit the one with the mutation. Men would transmit it to all of their offspring. Without a modifying normal gene on a second X chromosome, X-linked dominant conditions are frequently lethal in such males. The result is a vertical transmission pattern, usually from female to female.
