The Usher syndromes (USH) are a large group of inherited disorders which combine simultaneously both the hearing impairment and progressive loss of vision (similar to "Retinitis Pigmentosa" [RP]). Type 1 (USH1) is characterized by a congenital (present at birth), severe to profound and preverbal deafness, absent vestibular deterioration (balance) function and early onset of an RP-like retinal deterioration (typically by age 5 or 6 years and almost always before age 10 years.) Type II (USH2) has a milder (post-verbal) hearing loss, apparently present from birth, and a later onset (or detection) of an RP-like retinal degeneration (typically between ages 10-20 years). Balance functions are normal and stable, but the hearing impairment deteriorates very slowly, by some estimates an average of about 1 decibel (Db) per decade.
Although still controversial, the existence of at least a third type (USH3), distinguished from USH2 by the rapid and progressive nature of its hearing loss, has been suggested. USH3 seems to account for about 40% of Usher syndrome patients from eastern Finland; there is good genetics evidence that the gene for USH3 is located on a different chromosome than the locations of USH1 and USH2.
There may even be a rare Usher Syndrome Type IV, not yet well characterized.

All forms of RP and Rp-related disorders, like the Usher syndromes, are genetic, that is, caused by altered genes. However, the Usher syndromes are always autosomal recessive, that is, they occur with equal frequency and probability among males and females. Furthermore, an affected individual inherits one copy of the Usher gene from his mother and one copy from his father. Thus he has two Usher genes and no "normal" copy, and he (or she) is affected. In the usual situation each parent has one normal gene and one Usher gene, the effect of the normal copy predominates over the effect of the of the recessive copy so each parent functions with normal vision and normal hearing but genetically is a "carrier." within their genetic (and reproductive material).
When two carriers marry, there is one chance out of four at each conception/pregnancy that the child will inherit two Usher genes and be affected: 2 chances out of 4 that the child will inherit one Usher copy and normal copy and thus be a normal-functioning but genetic carrier just like each normal parent; and 1 chance out of 4 that the child will inherit a normal gene from mother and a normal gene from father and thus have two normal genes and function normally.