False negative results for IgA EmA and tTG testing are a common cause of negative diagnostic errors in CD and may occur as a consequence of total IgA deficiency (IgA serological levels < 5 mg/dL) or in case patients had already been started on a GFD or immunosuppressants at the time of serological testing [74,75]. Here, CD79A is linked to selective IgA deficiency disease.