X-Linked Disorders:

Hemophilia A is a bleeding disorder that can be caused by various pathogenic changes in the coagulation factor VIII gene, F8, of the X chromosome. These changes cause a deficiency in factor VIII clotting activity and although the DNA changes are different from each other, they are attributed to a similar presentation. The clinical signs of this disorder include prolonged or excessive bleeding after procedures and episodes of spontaneous bleeding, such as joint bleeds or deep-muscle hematomas (10). 

• The most common of these changes are inversions of intron 22, which is the reversal of the order of the DNA sequence, and occurs in 40-50% of Hemophilia A patients (9). 

• An inversion of intron 1 occurs in 5-7% of Hemophilia A patients (9). 

• Hemophilia A can also be acquired through a new genetic change rather than passed down from two carrier parents, meaning that it is caused by a de novo pathogenic change in an individual’s DNA.

Because Acquired Hemophilia A is very rare, there is often a delay in diagnosis due to a lack of family history of the disorder (11).

Written by Abigail Sayers; Images by Abigail Sayers unless otherwise noted

Reviewed and Edited by Rachel Baer, MSc, and Andy McCarty, MS, LGC, CGC

Learn More About Genetics:

• Sample Types

• Prenatal and Fetal Testing

• Aneuploidies

• Cytogenetics

Learn More About the X Chromosome:

• The X Chromosome

• X and Y Chromosomal Aneuploidies

• DMD and BMD

• Red-Green Color Blindness

• Alport Syndrome

• Fabry Disease

• Fragile X Syndrome

• Charcot-Marie-Tooth (CMT)