Researchers extensively studied how the various USH proteins bond together to form functional networks in the hair cells and photoreceptors.
They think they completely know these networks for USH 1, USH 2 and USH 3 and with that all associated proteins as well.
These networks contain only one protein which at this moment is not an USH protein. This is PDZD7, which forms a part of the networks of USH2 proteins. Mutations in this protein seem to cause only deafness. Whirlin is suspected to be able to compensate the functioning of PDZD7 in the eye but not in the ear. The fact is that these two proteins are very much alike.
Based on the similarity of the development of the disease it is thought that possibly four other genes may be associated with USH: PDZD7, HARS/USH3B, CEP250 and C2orf71. The interpretation may sometimes vary in different laboratories, e.g. some literature accepts USH 3B as USH gene and some literature only speaks of a possible association.
For USH 1E, 1H and 1K genomic regions have been defined, but genes with causal mutations have never been found in these regions. Expectations are that additional genetic analysis will show that these people still have mutations in one of the already known USH 1 genes.
In the Netherlands, people preferably take the work of Dr José Millán from Valencia, Spain, as a basis. He is the authority in the area of USH genetics in Europe. For a complete list of the presently known USH genes and mutations, please look here. This list comes from the publicly accessible on-line platform OMIM (Mendelian Inheritance in Man).
The Usher protein network. Red: associated with Usher Syndrome, Blue: associated with isolated RP and Black: associated with isolated deafness. Credits Erwin van Wijk