Various expression patterns of alpha1 and alpha2 genes in IgA deficiency

IgA deficiency (IgAD) is the most common immunodeficiency, however the pathogenesis in most cases of IgAD is unknown. There are 2 subclasses of IgA, IgA1 and IgA2, and its heavy chains are encoded by 2 different genes, the alpha1 and alpha2 genes. To investigate the molecular pathogenesis of IgA deficiency, it is important to evaluate each of the expressions of IgA1 and IgA2 separately.

In this study, we report on the reverse transcriptase (RT)-PCR method in which alpha1 and alpha2 mRNAs can be separately evaluated. This method is based on electrophoretic separation using the difference of 39 bases between alpha1 and alpha2 mRNAs. Three selective, 5 partial and 2 secondary IgAD patients were examined.

In the 3 selective IgAD patients, no alpha1 or alpha2 mRNA expression was detected. In the 5 partial IgAD patients, various alpha1 and alpha2 mRNA expression patterns were found. One of the partial IgAD patients showed only alpha2 gene expression, but not alpha1 gene expression, and was found to show an alpha1 gene deletion together with gamma 2 and epsilon gene deletions. His plasma IgA2 level was within the normal range.

Patients with an alpha1 gene deletion can be considered as having partial IgAD. Using this method, we identified the second case of alpha1 gene deletion in Japan, and classified IgAD patients on the basis of alpha1 and alpha2 expression.