Recent research has highlighted important differences between men and women in a wide range of areas of medicine, including heart disease, human immunodeficiency virus, depression, responses to pain and pain therapies, and drug pharmacodynamics (1). The influences of sex and gender are proposed to play a role in mediating these observed differences. Furthermore, an emphasis has been placed on the clarification of the terms sex and gender when describing the differences between men and women (2). In a report from the Institute of Medicine, sex is defined as "the classification of living things, generally as male or female according to their reproductive organs and functions assigned by the chromosomal complement," and gender as "a person's self-representation as male or female, or how that person is responded to by social institutions on the basis of the individual's gender presentation. Gender is shaped by environment and experience" (2). In other words, it is proposed that the term sex should be used to describe differences that are "primarily biological in origin and may be genetic or phenotypic," and the term gender should be used when "referring to social and cultural influences based on sex" (1). To avoid confusion in the review to follow, when appropriate, the authors have preferentially used either the terms gender or sex from the original references.This recognition and emphasis of the broad differences between men and women have made it important to consider a recent expert opinion "that not only may physicians need to make diagnostic and treatment decisions based on the sex of the patient, but they will also need to respond to gender differences in how women and men approach their physicians, their own health, and how they communicate their health concerns" (1). Although the general idea that men and women may have different manifestations and sequelae of the same disease may be intuitive, additional knowledge of the specific details in disease differences can assist in diagnostic and treatment issues and also provide hypotheses to test in the research arena.Ankylosing spondylitis (AS) is one such disease that has demonstrated distinct prevalence and clinical differences between men and women. With the recent treatment advances and the hope of halting the progression of the disease now a possibility, early recognition of the disease with its dependency on understanding the differences between men and women with AS will become increasingly important in the near future.The pathogenesis of AS in terms of both susceptibility and severity may be affected by both sex and gender factors. However, the exact pathogenesis of AS is still unknown and delineating the roles that either sex or gender factors play in the differences between men and women with AS is still problematic. The differences could be due to sex (i.e., genetic, hormonal, other phenotypic differences) or gender (i.e., society-or culture-related differences in physical activity, delay in diagnosis, environmental influences, infections, smoking, e...
