is a rare autosomal recessive disorder that is a leading cause of
deaf-blindness. It is associated with a mutation in any one of 10 candidate
genes. Usher syndrome is incurable at present. In
this disease, deafness is associated with a defective inner ear, and the vision
loss is associated with retinitis pigmentosa (RP), a degeneration of the
retinal cells. Usher syndrome has three clinical subtypes, denoted as I, II and
III in decreasing order of severity. People with Usher I (
are born profoundly deaf, begin to lose their vision in the first decade of
life and have problems with balance in movement. Different subtypes of Usher I
can be caused by mutations in any one of several different genes that function
in the development and maintenance of inner ear structures and transmit sound
and motion signals to the brain eg: CDH23, MYO7A, PCDH15, USH1C, and USH1G.
People with Usher II are also born deaf, but do not seem to have noticeable
problems with balance; they also begin to lose their vision later. Different
subtypes of Usher syndrome type II (MIM: Not available) may be caused by
mutations in any of three different genes: USH2A, GPR98 and DFNB31. People with
Usher syndrome III are not born deaf, but experience a gradual loss of their
hearing and vision; they may or may not have balance difficulties. Mutations in
only one gene, the CLRN1 gene, have been linked to Usher syndrome type III (
In India, Usher
syndrome is the second most common cause of deafness.
the studies done in India to date, this database presently holds the relevant
data for Usher I only caused by mutations in MYO7A.