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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.
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 ...
A white horse has mostly pink skin under its hair coat, and may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white (W) genes, are rare. Most horses that are commonly referred to as "white" are actually "gray" horses whose hair coats are completely white. Gray horses may be born of any ...
Horses heterozygous for the Ile118Lys mutation on the equine EDNRB gene—carriers of lethal white syndrome—usually exhibit a white-spotting pattern called "frame", or "frame overo". [5] [7] [9] [13] Frame is characterized by jagged, sharply defined, horizontally oriented white patches that run along the horse's neck, shoulder, flank, and ...
Individuals with this condition usually start showing signs of nyctalopia (also known as night-blindness) during their early childhood, increase in sensitivity to blue light, progressive decrease of visual acuity in both eyes, cataract, peripheral vision loss, vitreous liquefaction and detachment, clumped pigment deposits of the fundus, either peripheral or central retinoschisis, cystic ...