The Horse’s Karyotype Notice the absence of a Y- chromosome. It is a female horse.
Intro:• The horse has 32 pairs of chromosomes as compared to our 23• Some of the chromosomes correspond to ours or have similar functions (ex: the horse’s 27th chromosome is equivalent to our 21st)• Some disorders are fatal due to complications with internal organs and/or their functions, while others don’t have much effect of the horse’s usefulness• Since the horse’s genome hasn’t been extensively researched and explored, many generic disorders haven’t been pinned to a specific chromosome yet.
Overo Lethal White Syndrome• Lethal white overo (LWO), Overo lethal white syndrome (OLWS)• Caused by an autosomal recessive gene, this disorder is fatal 100% of the time. It causes a defective large intestine, which is narrow in one part causing a blockage. There is no treatment. OLWS foals are either euthanized or die of colic in the first few days of life, they cannot pass stool.• All breeds with white and patterned coats are at risk including thoroughbreds, quarter horses, and, predominantly, the paint horse breed. The disorder can only be prevented through careful and responsible breeding.• All horses in breeding programs that are suspected of being carriers should be tested for the gene. Carrier horses usually have a certain coat pattern called the frame, which is a sought after color. more info back to table of contents
More Info • Although a horse may have the frame pattern, he may not carry the OLWS gene • Not all white foals born are OLWS foals, some just have a white coat • Many carrier horse areA horse with the frame pattern. He is a bred either intentionallycarrier of the lethal white gene. or accidentally because the frame coat is a very popular coat back to table of contents
Glycogen Branching Enzyme Deficiency• Glycogen Branching Enzyme Deficiency (GBED)• This disorder is caused by a recessive, mutated gene. Foals affected with the disorder are missing the enzyme that turns glucose into glycogen, the fuel for the muscles, heart and brain. Therefore it is fatal; no fuel, no foal. Many of the affected foals are stillborn or miscarried. Some are born alive, but none have survived past 3 months. There is no treatment.• It is present mostly in quarter horse and paint horse breeds. The gene is present in approximately 10% of all quarter horses. The only prevention is carefully planned and responsible breeding. Have all horses that are being bred tested for the gene. back to the table of contents
Lavender Foal Syndrome• Coat Color Dilution Lethal (CCDL), Lavender Foal Syndrome (LFS)• This disorder is most commonly found in Egyptian Arabians. It is present in approximately 10% of all Egyptian Arabians, although it has been reported in other breeds. The foals generally have a complicated birth, and cannot stand. Their coat is usually pale, and can look pink, silver, or lavender (hence the name). It is thought to be caused by a brain lesion.• Currently, the inheritance pattern has not been established, but research points towards the condition being autosomal recessive. There is no treatment, all foals die within a few days. Prevention consists of careful breeding and testing for the gene and carrier horses. back to table of contents
Severe Combined Immunodeficiency Disorder• Severe Combined Immunodeficiency Disorder (SCID)• This disorder causes foals to be born without an immune system and without the means to build up one. Affected foals will die within 4 to 6 months without any intervention. Few cases have been corrected with bone marrow transplants, however this is expensive and not always effective. For most affected foals, the condition is fatal.• It is an autosomal recessive disorder found mostly in Arabian horses and related breeds. Between 15 and 28% of Arabian horses are carriers. back to table of contents
Junctional Epidermolysis Bullosa• Junctional Epidermolysis Bullosa (JEB)• Caused by a recessive mutation, this disorder results in the absence of a protein that keeps the hoof wall and skin structure intact.• It usually occurs in Belgian horses and other draft breeds. Foals will die within 7-14 days because of infection in sores on the skin from pressure points or because of the disconnection of the hoof wall.• Unfortunately, there is no cure. Prevention includes: having draft horses in the breeding stock tested, and not breeding two carrier horses together. back to the table of contents
Equine Juvenile Epilepsy• Equine Juvenile Epilepsy (EJE), Juvenile Epilepsy Syndrome (JES), Juvenile Idiopathic Epilepsy (JIE)• This disorder causes seizures in young horses and is usually outgrown by 18 months of age. It is unclear what causes it, and how it is inherited. EJE is common in Arabian horses and related breeds.• Affected foals must be kept in safe enclosures to prevent harm if the foal were to have a seizure and fall to the ground. They are also given anti-seizure medication. It is usually not lethal unless the foal is seriously injured during a seizure.• There are no tests for the disorder, so therefore no means of prevention. EJE horses are perfectly normal once they mature. back to the table contents
Guttural Pouch Tympany• Guttural Pouch Tympany (GPT)• Thought to be in a polygenetic gene, this disorder causes the Eustachian tube (entrance to the windpipe) to act as a one way passage. As a result, air builds up behind the jawbone making it difficult for the horse to breathe. This can be fixed temporarily by the insertion of a catheter to allow air to escape. If this does not fix the problem, surgery is required, however the outlook is good.• GPT usually shows up in horses from six months to a year and a half, but it can come up at any point in life. Females are about four times as likely to inherit the disorder than males. Many breeds are affected including (but not limited to) Arabians, warmbloods, and Quarter Horses. Since the cause of the disorder and specific genes affected are unknown, there isn’t much prevention other than not breeding affected horses. back to table of contents
Hairless Foal Syndrome• Hairless Foal Syndrome (HFS), Naked Foal Syndrome (NFS)• HFS causes minimal keratin production resulting in a foal born with no hair. It is passed recessively. It is a rare occurrence for all breeds, but shows up more often in Ahal-Teke horses. Affected foals are born without any or little hair. Hoof and digestive problems are common in these horses. In Ahal-Teke horses, it is lethal because of the severity of the inhibited keratin production.• Affected horses of this breed and other light breeds usually die in the first two years of life because of laminitis (non hereditary condition of the hooves) or digestive problems. Draft horses with the disorder usually can make it to their late teens because they tend to have stronger hooves and are more hardy. These horses must be properly cared for: blanketed, turned out only at night, skin moisturizer, balanced diet, etc. back to table of contents
Equine Dwarfism• This disorder causes foals to be born extremely small in stature and generally out of proportion. There are four known types or variations of the gene – Type 1: Diastrophia: these foals have twisted legs and other extremities. It is the least severe form of equine dwarfism – Type 2: Achondroplasia: this form produces foals with short legs, necks, etc in comparison to their bodies – Type 3: Brachiocephalia: The foals affected have very compact bodies with short necks, large heads, and pot bellies. – Type 4: Hypochondrogenesis: These foals are underdeveloped and not carried to term. They are very small and have extreme deformities.• All types are recessively inherited. The disorder is most commonly found in miniature horses (proportional to normal horses), however type 1 has been found in Fresians.• Dwarfs foals with leg deformities can sometimes be casted to encourage normal leg growth. Braces and sometimes even surgery can correct more serious problems. back to the table of contents
Trisomy 27• This disorder is caused by nondisjunction of the 27th chromosome. Any horse can potentially be affected. Not many cases have occurred on record. One of them, a Standardbred colt. He was born with an abnormal personality, and was slow in picking up on social cues from other horses and seemed to violate the others’ “personal space”.• Many abnormalities in this colt were similar to those seen in children with Down syndrome (Trisomy 21). Other trisomies have occurred in horses including: 23, 26, 27, 28, 30, and 31. Although the colt was euthanized at 24 months, he showed no physical signs that he could not have led a somewhat normal life and matured into an adult. back to table of contents
Hereditary Equine Regional Dermal Asthenia• Hereditary Equine Regional Dermal Asthenia (HERDA), Hyperelastosis Cutis (HC)• This connective tissue disorder causes skin in certain areas to be extremely thin and fragile making them prime candidates for infection and slow healing. Cornell and Mississippi State are working to find the affected gene and research how the gene is expressed.• Mild cases managed well on special diets and restricted turnout can sometimes be ridden with the right equipment. However this isn’t the case for most affected horses who are either euthanized or donated for research by age 4. Many carriers and affected horses are inbred and can be traced back to one quarter horse sire, Poco Bueno. Paint and Appaloosa horses are also affected by the disorder. The homozygous recessive disorder can be directly tested for and carriers should not be bred together. back to table of contents
Hyperkalemic Periodic Paralysis• Hyperkalemic Periodic Paralysis (HYPP)• An autosomal dominant muscle disorder, HYPP causes sudden, unexplained muscle twitches, collapse, and paralysis mainly in the Quarter Horse breed. The disease can be traced back to Impressive, a halter horse stud from the 70’s and 80’s. Heterozygous individuals are less likely to have attacks than homozygous HYPP horses, but it is still possible. The muscles of HYPP affected horses take less influence to contract, making them prone to collapse and/or seize randomly. These horses can die from an attack because the pharynx and larynx collapse or because the heart develops arrhythmia that cannot be stopped. Any kind of stress or heavy sedation can trigger an episode on affected horses. Blood or hair samples can be tested for the gene. The American Quarter Horse Association (AQHA) has taken active measures to prevent against the disorder. As of January 1st, 2007, they require that all foals in the bloodline of Impressive be tested for HYPP and any foal of any bloodline that tests homozygous positive cannot be registered. back to table of contents
Degenerative Suspensory Ligament Desmitis• Degenerative Suspensory Ligament Desmitis (DSLD), Equine Systemic Proteoglycan Accumulation (ESPA)• The condition causes the suspensory ligament to loose the ability to support the horse’s weight. More advanced cases show the pastern dropping towards the ground. In later stages, it can be very painful for the horse. If caught early on, the progression can be slowed with corrective shoeing and diet adjustments varying case to case.• It has appeared in the Quarter Horse, Saddlebred, Arabian, Paso Fino, and Thoroughbred. There has not been extensive research on the inheritance and prevention of the disorder, therefore the mode of inheritance and preventative measures are still widely unknown. back to table of contents
back to table of contents Works Cited:"Advanced Topics." The Equine Tapestry. 3 Nov. 2011. Web. Feb. 2012. <http://equinetapestry.com/category/advanced-topics/>."DSLD." Horseshoes.com. Web. 27 Feb. 2012. <http://www.horseshoes.com/anatomy/esad/information/dsld/dsld.htm>."Equine Genetic Disease: Whos At Risk?" TheHorse.com. Web. 27 Feb. 2012. <http://www.thehorse.com/ViewArticle.aspx?ID=6169>."Equine Medical Services." Genetic Disorders :. Web. 27 Feb. 2012. <http://www.equmed.com/?cat=5>."Genetics and Genetic Disorders." Welcome to ArabianHorses.org. Arabian Horse Association. Web. 27 Feb. 2012. <http://www.arabianhorses.org/education/genetic/default.asp>."Guttural Pouch TympanyBy: Dr. Melissa Mazan." Guttural Pouch Tympany. Web. 27 Feb. 2012. <http://www.petplace.com/horses/guttural-pouch-tympany/page1.aspx>."Horse Forum." HORSE FORUM. Copyright 2008 - Horse Grooming Supplies, 2008. Web. 2011. <http://www.horsegroomingsupplies.com/horse-forums/breeders-guide-to-equine-genetic-disorders- 367267.html>."Juvenille Epilesy." Genetic Disorders. Arabian Horse Association. Web. Feb. 2012. <http://www.arabianhorses.org/education/genetic/docs/Juvenile_Epilepsy.pdf>."Lethal Chart." Lethal Chart. Photobucket. Web. Feb. 2012. <http://i872.photobucket.com/albums/ab283/talkingmongo0se/Lethal-Breeding-Chart.png lethal>."Simple Dominant Breeding Chart." Simple Dominant Breeding Chart. Web. Feb. 2012. <http://i872.photobucket.com/albums/ab283/talkingmongo0se/Simple-Dominant-Breeding-Chart.png>."Simple Recessive Breeding Chart." Simple Recessive Breeding Chart. Photobucket. Web. Feb. 2012. <http://i872.photobucket.com/albums/ab283/talkingmongo0se/Simple-Recessive-Breeding-Chart.png recessive>.Thomas, Heather S. "Genetic Diseases in Quarter Horses and Related Breeds." The Equine Chronicle. Heather Smith Thomas, July-Aug. 2009. Web. Feb. 2012. <http://www.equinechronicle.com/health/genetic-diseases-in-quarter-horses-and-related-breeds.html>.