Aetiology

In adults, pernicious anaemia is an auto-immune disorder.

Auto-antibodies to gastric parietal cells are present in 90% of cases but are not pathognomonic as they may occur:

• in other disorders, for example, Addison's disease; iron deficiency anaemia
• in normal relatives of those with PA
• in 16% of randomly selected women over 60 years

Auto-antibodies to intrinsic factor are more specific. They are found in the serum in 55% of cases and in gastric juice in 80%. They are of two types:

• blocking antibody - directed towards the combining site for vitamin B12 on IF
• binding antibody - reacts with an antigenic determinant on IF distinct from the B12 combining site; the reaction may be with free IF or with IF-B12 complex in the terminal ileum to inhibit absorption.

In children pernicious anaemia may occur very rarely due to congenitally absent or abnormal intrinsic factor.