Fabry disease is inherited in a X-linked manner. This refers to the location of the gene for the enzyme alpha-galactosidase A, which is found on the X chromosome. The X and Y chromosomes, two of the 23 pairs of chromosomes in the human body, among many other functions determine the sex of an individual. Females have two X chromosomes. Males have one X chromosome and one Y chromosome.
Affected males pass their one affected X chromosome to all of their daughters. In this way, all daughters of affected males are considered "obligate carriers" of the gene for Fabry disease. This is assuming paternity is not of concern.
Whether or not a female is so-called "affected" by Fabry disease must be determined on an individual basis. Some females are as affected by the symptoms of Fabry disease as severely as a male with the classic form of the disease, while others may be seemingly asymptomatic or only experience mild symptoms, or an individual exhibit any variation of symptoms in between.
Researchers and treating physicians have learned in recent years, however, that females without symptoms is the exception rather than the rule. A very high percentage of females carrying the Fabry disease gene are affected and have significant disease symptoms warranting treatment with Enzyme Replacement Therapy.
Affected males do not pass the Fabry disease gene to any of their sons; sons receive their father's Y chromosome and therefore, a son cannot inherit Fabry disease from an affected father.
Every time a carrier female has a child, there is a 50% chance that she will pass her affected X chromosome to the child, and a 50% chance that she will pass her normal X chromosome to the child. This means that there is a 50% chance that every daughter born to a carrier female will inherit the affected X chromosome and will be a carrier (and possibly symptomatic/affected) for Fabry disease. There is a 50% chance that every son born to a carrier female will inherit his mother's affected X chromosome, and will therefore, be affected with Fabry disease.