Leopard complex
Secondary characteristics associated with the leopard complex include a white sclera around the eye, striped hooves and mottled skin.
[3] A number of factors, each separately, genetically controlled, interact to produce familiar patterns such as "snowflake," "leopard," and "fewspot".
A DNA test can now identify the Lp gene, though a combination of pedigree knowledge and coat characteristics also help.
While both heterozygous and homozygous Lp horses possess the aforementioned characteristics, heterozygotes and homozygotes differ significantly in the presence of true spots.
True leopard spots are produced only by the Lp gene, and directly reflect the underlying coat color (bay, black, gray, cremello, red dun, and so on).
[2] Even horses with extensive white usually retain dark colored regions just above the hooves, on the knees and hocks, stifles and elbows, hips and points of shoulder, the tail, mane, and the bony parts of the face.
[7] The leopard complex allele contains a 1378 bp long terminal repeat insertion of retroviral DNA which disrupts transcription of TRMP1.
This finding represents evidence for the presence of leopard complex spotting in prehistoric wild horse populations.
The ancient origin of the allele may explain the presence of spotted horse paintings in paleolithic cave art.
Horses with CSNB may be hesitant to enter dimly-lit places - such as indoor arenas, dark stalls, or trailers - and be apprehensive when in such conditions, which may interfere with handling or riding.
It is thought that these cells fail to undergo the basic chemical reaction for nerve impulse transmission, which involves shuttling of calcium (Ca2+).
However, one study used ERG findings to diagnose all the homozygous Lp subjects with CSNB, while all heterozygotes and non-Lp horses were free from the disorder.
[8] The gene to which Lp has now been localized encodes a protein that channels calcium ions, a key factor in the transmission of nerve impulses.
This protein, which is found in the retina and the skin, existed in fractional percentages of the normal levels in homozygous Lp/Lp horses.
[16] Up to 80% of all uveitis cases are found in Appaloosas, with physical characteristics including light colored coat patterns, little pigment around the eyelids and sparse hair in the mane and tail denoting more at-risk individuals.
[4][8] The existence of leopard-spotted coats among Asian breeds such as the Karabair and Mongolian Altai has been recorded since ancient times, and suggests that the gene is very old.
