We read with interest the article by Weinreich and colleagues.1 They showed that transgenic mice born to mothers aged 8 months or older had a significantly lower frequency of murine ankylosing enthesopathy than mice born to younger mothers. They speculated that an age related increase in maternal antibody levels resulted in increasing protection of offspring against a ubiquitous, potentially arthritogenic, micro-organism. In humans, as in the mouse model, environmental factors must influence the development of ankylosing spondylitis (AS). We sought evidence that the age of conception in women with AS influenced the risk of their offspring developing disease.

We collected data from …