Coeliac disease
People of African, Japanese and Chinese descent are rarely diagnosed; this reflects a much lower prevalence of the genetic risk factors, such as HLA-B8. People of Indian ancestry seem to have a similar risk to those of Western Caucasian ancestry. Population studies also indicate that a large proportion of coeliacs remain undiagnosed; this is due, in part, to many clinicians being unfamiliar with the condition and also due to the fact it can be asymptomatic. Coeliac disease is slightly more common in women than in men. A large multicentre study in the U.S. found a prevalence of 0.75% in not-at-risk groups, rising to 1.8% in symptomatic people, 2.6% in second-degree relatives (like grandparents, aunt or uncle, grandchildren, etc.) of a person with coeliac disease and 4.5% in first-degree relatives (siblings, parents or children). This profile is similar to the prevalence in Europe. Other populations at increased risk for coeliac disease, with prevalence rates ranging from 5% to 10%, include individuals with Down and Turner syndromes, type 1 diabetes, and autoimmune thyroid disease, including both hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid).