Skewed Inactivation of X Chromosome: A Cause of Hemophilia Manifestation in Carrier Females

Abstract

Hemophilia is an X-linked recessive hereditary disorder that classically affects males due to the presence of only one X chromosome in males. Females are usually carriers due to the presence of counterpart X chromosome, but many times manifestations of hemophilia are seen in heterozygous carrier females. This is a result of skewed lionization, in which more normal X chromosomes are converted to bar body, and more abnormal chromosomes remain active in body cells, causing the dominant manifestation of the disease. The severity of manifestations is directly proportional to the level of the clotting factor in the blood. The disease can be severe enough to cause life-threatening bleeding, especially during delivery. Physicians usually reluctant to assume hemophilia in the differential diagnosis of the bleeding disorders in women but manifesting carrier females with hemophilia are not uncommon. Our review of the literature will give an opportunity to understand this issue more precisely as well as will discuss the disease manifestations and its updated management.

Keywords: bar body; clotting disorder; hemophilia; lyonization.

Figure 1. Pedigree: X-linked recessive inheritance

Rectangle: male; circle: female; filled rectangle: affected male; dotted circle: affected female. Female 2 (II) passed hemophiliac X to her son 1 (III).

Figure 2. X chromosome inactivation pattern in hemophilia carrier females