Allergists focus on traditional medical issues of acuity, life and death. IgG issues most often arise in the evaluation of chronic illness that often presents as refractory mental problems - like ADHD.
Let's face the naming thing squarely, head on. ADHD and ADD labels provide more confusion than understanding, more complexity than common sense. Why, because they describe symptoms that remain on the surface.
Each one of these 4 neurotransmitters in this list is associated with a link that will take you further down the ADHD neuronal/glial communication path.