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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.
[3] [14] Additionally, hearing loss is not as common as in type 2. [3] Rarely, cleft lip has been reported in this form of Waardenburg syndrome. [15] Type 4 can also be caused by a mutation in SOX10 (the same gene as in type 2E), in which it is known as type 4C; hearing loss is very common and severe in this type. [16]
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]
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 ...
Usually, individuals with this condition have cerebellar ataxia, areflexia, high-arched feet, optic nerve wasting/degeneration, sensorineural deafness. [5]These symptoms have variable onset, but they generally begin episodically after having a fever-causing infection such as the common cold, manifesting mainly as sudden-onset ataxic episodes and encephalopathy.
Whether a horse visually appears to have the frame pattern or not, testing horses of frame or "overo" lineage is highly recommended. The statistical likelihood of producing a living, frame-patterned foal by crossing two frames is 50%, the same odds of producing a living, frame-patterned foal from a frame-to-nonframe breeding which carries no ...
Other causes of congenital hearing loss that are not hereditary in nature include prenatal infections, illnesses, toxins consumed by the mother during pregnancy or other conditions occurring at the time of birth or shortly thereafter. These conditions typically cause sensorineural hearing loss ranging from mild to profound in degree. [3]