Semin Reprod Med 2001; 19(2): 183-192
DOI: 10.1055/s-2001-15398
Copyright © 2001 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel.: +1(212) 584-4662

Skewed X Inactivation in X-Linked Disorders

Ignatia B. Van den Veyver1
  • Departments of Obstetrics and Gynecology and of Molecular and Human Genetics, Divisions of Maternal-Fetal Medicine and of Reproductive Genetics, Baylor College of Medicine, Houston, Texas
Further Information

Publication History

Publication Date:
31 December 2001 (online)


X chromosome inactivation is a process by which the dosage of proteins transcribed from genes on the X chromosome is equalized between males (XY) and females (XX) through the silencing of most genes on one of the two X chromosomes in females. Although the choice of which of the two X's is inactivated is entirely random, not all women have a 50:50 ratio of cells with one or the other X chromosomes active. A number of different mechanisms lead to extremely skewed ratios and this can result in expression of the phenotype of X-linked recessive disorders in females. Nonrandom X inactivation patterns are also associated with selective female survival in male-lethal X-linked dominant disorders or with variable severity of the phenotype in women carrying X-linked dominant mutations. These features are important for the study and gene identification of X-linked disorders and for counseling of affected families.