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Congenital stationary night blindness (CSNB) can be inherited in an X-linked, autosomal dominant, or autosomal recessive pattern, depending on the genes involved. Two forms of CSNB can also affect horses, one linked to the leopard complex of equine coat colors and the other found in certain horse breeds. Both are autosomal recessives.
Congenital stationary night blindness has been linked with the leopard complex since the 1970s. [14] The presence of CSNB in non-leopard breeds and horses suggested that the two conditions might be located on close, but separate genes.
Congenital stationary night blindness (CSNB) is usually diagnosed based on the owner's observations, but some horses have visibly abnormal eyes: poorly aligned eyes (dorsomedial strabismus) or involuntary eye movement (nystagmus). [8] In horses, CSNB has been linked with the leopard complex color pattern since the 1970s. [9]
Appaloosas that are homozygous for the leopard complex (LP) gene are also at risk for congenital stationary night blindness (CSNB). [105] This form of night blindness has been linked with the leopard complex since the 1970s, [106] and in 2007 a "significant association" between LP and CSNB was identified.
Congenital Stationary Night Blindness (CSNB2) is a heritable genetic condition that has been found in some Tennessee Walking Horses. It is a recessive missense mutation in the GRM6 gene and is believed to inhibit the ability of the ON-bipolar cell to uptake glutamate. [10]
Homozygous leopards are substantially more prone to congenital stationary night blindness. [9] Congenital stationary night blindness is present at birth and is characterized by impaired vision in dark conditions.
One result of the mapping of the horse genome was locating the mutation that creates the Leopard complex (Lp) spotting pattern seen in breeds such as the Appaloosa. [2] Horses homozygous for the Lp gene are also at risk for congenital stationary night blindness (CSNB). [6]
The complete form of congenital stationary night blindness is due to the absence of nyctalopin. [16] This absence is due to a mutation involving an 85 base pair deletion. [ 17 ] In humans, more than 30 mutations are found in the NYX gene and most of them have an impact either on the tertiary structure of the LRR domains of nyctalopin or to ...