Exquisite resource page, thank you Pankaj Sah, very useful for clients and service providers. Now we just need something like this as a resource for researchers as well.
There really are few studies about deafblindness. Here in Brazil is Ahinsa institute that helps children with deafblindness and multiple sensory disability. This link find some searches applied to this in Portuguese language: http://www.ahimsa.org.br/eventos.html
A old research on deafblindness is the researcher Lev Vygotsky in the special school Zagorsky in Russia. This study inspired the movie "The Butterflies of Zagorsk".
In my opinion combined cases of ear and eye involvement -Succaka syndrome, etc. could be published in Neurology Journals, taken into account the hyghest nervous centrs in the brain and also in General Medical Journals -JAMA, the Lancet.