X-linked dominant

X-linked dominant is mode of inheritance in which a gene on the X chromosome is dominant. [ [http://www.lpch.org/DiseaseHealthInfo/HealthLibrary/genetics/xdomin.html X-linked Dominant: Incontinentia pigmenti - Lucile Packard Children's Hospital] ] Females can be more frequently affected than males since they have two X chromosomes that could potentially carry the abnormal gene, whereas a male has only one. However, the Lyon hypothesis states that X-inactivation renders only one copy of the X chromosome active in each cell hence on average one would expect only one half of the cells to express the abnormal gene. The chance of passing on an X-linked dominant disorder differs between men and women.

As a disease inheritance pattern, it is less common than X-linked recessive.

Inheritance

Females usually have two X chromosomes, while most males have one X and one Y chromosome. If a child has inherited the mutation from the X chromosome of one of their parents they will have the condition. A woman with an X-linked dominant disorder has a 50% chance of having an affected daughter or son with each pregnancy. The sons of a man with an X-linked dominant disorder will not be affected (since they inherit their only X chromosome from their mother), but his daughters will all inherit the condition.

Some X-linked dominant conditions such as Aicardi Syndrome are fatal to boys, therefore only girls with these conditions survive. Similarly, individuals with Klinefelter's Syndrome are referred to as "47,XXY Males".

See also

*Hypophosphatemia
*Rett syndrome
*Sex linkage

References