Please note: Disease penetrance and incidence in breeds can vary according to populations and geographical regions. Some diseases for that breed may not be relevant to the population in that country. For relevance of a particular disease we recommend you consult your breed club or feline health professional. It is recommended that if the disease is considered not relevant to your population then you screen for all potential diseases if importing a stallion or semen for breeding purposes.
1red Scale 1 a very low degree of severity, It is a trait and so is tested based on preference, not for usually health concerns.
2red Scale 2 has a low degree of severity, as it generally poses no health concerns.
3red Scale 3 has a moderate degree of severity, as it is not a fatal disease, thought it can decrease the quality of life.
4red Scale 4 has a high degree of severity due to the affects on affected horses, often results in a decreased quality of life and life span.
5red Scale 5 has an extreme degree of severity. It can cause significant decrease of quality of life and immediate death.

Equine Disease
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Hyperkalemic Periodic Paralysis



Category: Metabolic / Muscular

Mode of Inheritance:
Autosomal Dominant (incomplete penetrance)

Severity:
4red

Description:
Hyperkalemic periodic paralysis (HYPP) is an inherited disease of the muscle which is caused by a genetic defect. In the muscle of affected horses, a point mutation exists in the sodium channel gene and is passed on to offspring.
Sodium channels are "pores" in the muscle cell membrane which control contraction of the muscle fibers. When the defective sodium channel gene is present, the channel becomes "leaky" and makes the muscle overly excitable and contract involuntarily. The channel becomes "leaky" when potassium levels fluctuate in the blood. This may occur with fasting followed by consumption of a high potassium feed such as alfalfa. Hyperkalemia, which is an excessive amount of potassium in the blood, causes the muscles in the horse to contract more readily than normal. This makes the horse susceptible to sporadic episodes of muscle tremors or paralysis.
HYPP is characterized by sporadic attacks of muscle tremors (shaking or trembling), weakness and/or collapse. Attacks can also be accompanied by loud breathing noises resulting from paralysis of the muscles of the upper airway. Occasionally, sudden death can occur following a severe paralytic attack, presumably from heart failure or respiratory muscle paralysis

Reference:
1. Spier, SJ, Carlson, GP, Holliday, TA, et al. Hyperkalemic periodic paralysis in horses. J Am Vet Med Assoc. 1990; 197: 1009-1017.
2. Cox, JH and DeBowes, RM. Episodic weakness caused by hyperkalemic periodic paralysis in horses. Comp Cont Educ Pract Vet (Equine) 1990; 12:83-89.
3. Naylor, JM, Robinson, JA, and Bertone, J. Familial incidence of hyperkalemic periodic paralysis in Quarter Horses. J Am Vet Med Assoc. 1992; 3:340-343.
4. Rudolf, JA, Spier, SJ, Byrns, G, and Hoffman, EP. Linkage of hyperkalemic periodic paralysis in Quarter Horses to the horse adult skeletal muscle sodium channel gene. Animal Genetics 1992: 23: 241-250.
5. Spier, SJ, Carlson, GP. Hyperkalemic periodic paralysis in certain registered Quarter Horses. The Quarter Horse Journal 1992, pp. 68-69, 120.
6. Zhou, J, Spier, JS, Beech, J, and Hoffman, EP. Pathophysiology of sodium channelopathies: correlation of normal/mutant mRNA ratios with clinical phenotype in dominantly inherited periodic paralysis. Human Molecular Genetics 1994; 3: 1599-1603.
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Lethal White Overo

Pasted Graphic

Category: Intestinal

Mode of Inheritance:
Autosomal Dominant

Severity:
5red

Description:
Lethal White Overo (LWO) syndrome occurs when a horse is homozygous (OO) for the frame overo gene. This genetic disorder causes the intestinal system not to develop properly (involving aganglionosis of the bowel). The foal will die within the first 72 hours after birth when its first meals cannot be digested properly. The lethal white foal will be born almost pure white.
This genetic abnormality is caused by a mutation of the EDNRB protein. Horses that do not have LWO syndrome can still be carriers of the LWO gene. When they are carriers of this gene, they are said to be heterozygous (
nO) for the LWO gene and may pass it on to offspring. The heterozygous LWO gene in a horse occurs when the diploid (one copy from mother and one from father) of the LWO gene contains one frame overo copy and one non-frame overo copy and is often referred to as positive for frame overo.
Reference:
1. Vonderfecht, SL; Bowling AT, Cohen M (January 1983). "Congenital intestinal megacolon in white foals". Veterinary Pathology (The American College of Veterinary Pathologists) 20 (1): 65–70. PMID 6849219.
2. McCabe L, Griffin LD, Kinzer A, Chandler M, Beckwith JB, McCabe ER (July 1990). "Overo lethal white foal syndrome: equine model of aganglionic megacolon (Hirschsprung disease)". Am. J. Med. Genet.
36 (3): 336–40. PMID 2363434.
3. Vrotsos, PD; Santschi EM, Mickelson JR (2001).
"The Impact of the Mutation Causing Overo Lethal White Syndrome on White Patterning in Horses" (PDF). Proceedings of the Annual Convention of the AAEP 2001 (American Association of Equine Practitioners) 47: 381–91.Retrieved 2008-09-05
4. "Lethal White Overo (LWO)". Animal Genetics, Inc.. http://www.horsetesting.com/LWO.htm. Retrieved May 21, 2010.

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Glycogen Branching Enzyme Deficiency

GBED

Category:
Metabolic

Mode of Inheritance:
Autosomal Recessive

Severity:
5red

Description:
Glycogen branching enzyme deficiency (GBED) occurs in newborn foals. This fatal disease is seen in Quarter Horses and related breeds. The foals lack the enzyme necessary to store glycogen (sugars) in its branched form and therefore cannot store sugar molecules. This disease is fatal as the heart muscle, brain and skeletal muscles are unable to function.The clinical presentation of this disease is variable. Late term abortion or stillbirth is described for GBED. Recent research suggests that at least 3% of abortions in Quarter horses are due to GBED. Some foals are born alive but are often weak and require warming and assistance to nurse after birth. These foals may appear healthy for a time but eventually the may develop seizures, become too weak to stand, or in some cases, they die suddenly. Owners may note that GBED foals are less active than other foals. In spite of aggressive treatment, all known cases of GBED have been euthanized or died by 18 weeks of age.

Reference:
1. Valberg SJ, Mickelson JR, Ward TL, Rush B, Kinde H, Hiraragi H, Nahey D, and Fyfe J. Glycogen branching enzyme activity in Quarter Horse foals. J Veterinary Internal Medicine 2001;15:572-580.
2. Render JA, Common RS, Kennedy FA, Jones MZ, Fyfe JC: Amylopectinosis in fetal and neonatal Quarter Horses. Veterinary Pathology 1999: 36(2):157-60.
3. Sponseller BT, Valberg SJ, Ward T, Williams AJ. And Mickelson JR. Muscular weakness and recumbency in a quarter horse colt due to glycogen branching enzyme deficiency. Equine Vet Educ 2003;14:182-188.
4. Tay SKH, Akman HO, Chung W, Pike MG, Hays AP, Anyane-Yeboa K, Shanske S, Tanji K. Mickelson J R, Valberg SJ , DiMauro S. Fatal Neonatal Presentation of Glycogen Storage Disease Type IV Neuromusc Disorders 2004 ;4:253-260.
5. Valberg SJ, Mickelson JR, Ward TL, Rush B, Kinde H, Hiraragi H, Nahey D, and Fife J. 2001. Glycogen branching enzyme activity in Quarter Horse foals. J Vet Intern Med. 15:572-580.
6. Wagner ML, Valberg SJ, Ames EG, Bauer MM, Wiseman JA, M. Penedo MCT, Kinde H, Abbitt B, and Mickelson JR. Allele frequency and likely impact of the glycogen branching enzyme deficiency gene in Quarter Horse and Paint Horse population s. Animal Genetics, submitted
7. Ward TL, Valberg SJ, Lear T, Guerin G, Milenkovic D, Swinburne J, Binns MM, Raudsepp T, Skow L, Chowdhary BP, and Mickelson JR. Genetic mapping of GBE1 and its association with glycogen storage disease IV in American Quarter Horses. Cytogenet Genome Res 2003; 102:201-206.
8. Ward TL, Valberg SJ, Adelson DL, Abbey CA, Binns MM, and Mickelson JR. (2004). Glycogen branching enzyme ( GBE1 ) mutation causing equine glycogen storage disease IV. Mamm Genome 15, 570-577.
9. Ward TL, Valberg SJ , Adelson DL, Abby CA 3 , and James R Mickelson JR Glycogen Branching Enzyme (GBE1) Mutation Causing Fatal Glycogen Storage Disease IV in American Quarter Horse Foals Mammalian Genome 2004;15:570-577.
10. Wagner ML, Valberg SJ, Ames EG, Bauer MM, Wiseman JA, Penedo CT, Kinde H,  Abbitt B, and Mickelson JR. Allele Frequency and Likely Impact of the Glycogen Branching Enzyme Deficiency Gene in Quarter Horse and Paint Horse Populations. J Vet Int Med 2006; Sep-Oct;20(5):1207-11


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Junctional Epidermolysis Bullosa

Picture 1

Category:
Cutaneous

Mode of Inheritance:
Autosomal Recessive

Severity:
4red

Description:
Junctional epidermolysis bullosa (JEB) is an inherited disease that causes moderate to severe blistering of the skin and mouth epithelia, and sloughing of hooves in newborn foals. This condition is also known as red foot disease. Affected foals are typically born alive, but soon develop skin lesions at pressure points. The condition worsens with time and the foal eventually succumbs from severe infection or has to be euthanized.
JEB in Belgian Draft horses has been shown to be the result of a specific mutation in a gene that affects the production of normal and healthy skin. To date, this mutation has been found only in Belgian Draft horses and derivatives of that breed.
Reference:
F. Spirito et. al., J Invest Dermatol 119:684-691, 2002.
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HERDA (Hereditary equine regional dermal asthenia)

HERDA

Category:
Cutaneous

Mode of Inheritance:
Autosomal Recessive

Severity:
3red

Description:
Hereditary equine regional dermal asthenia (HERDA) is a genetic skin disease predominantly found in the Quarter Horse. Within the breed, the disease is prevalent in particular lines of cutting horses. HERDA is characterized by hyperextensible skin, scarring, and severe lesions along the back of affected horses. Affected foals rarely show symptoms at birth. The condition typically occurs by the age of two, most notably when the horse is first being broke to saddle. There is no cure, and the majority of diagnosed horses are euthanized because they are unable to be ridden and are inappropriate for future breeding.
Reference:
1. Hardy MH, Fisher KR, Vrablic OE, et al. (August 1988). "An inherited connective tissue disease in the horse". Laboratory Investigation 59 (2): 253–62. PMID 3404977.
2. Brounts SH, Rashmir-Raven AM, Black SS (August 2001). "Zonal dermal separation: a distinctive histopathological lesion associated with hyperelastosis cutis in a Quarter Horse". Veterinary Dermatology
12 (4): 219–24. PMID 11493407.
3. White SD, Affolter VK, Bannasch DL, et al. (August 2004). "Hereditary equine regional dermal asthenia ("hyperelastosis cutis") in 50 horses: clinical, histological, immunohistological and ultrastructural findings". Veterinary Dermatology
15 (4): 207–17
4. Tryon RC, White SD, Bannasch DL (July 2007). "Homozygosity mapping approach identifies a missense mutation in equine cyclophilin B (PPIB) associated with HERDA in the American Quarter Horse". Genomics
90 (1): 93–102

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Severe Combined Immuno-Deficiency (SCID)

Category:
Immunologiocal

Mode of Inheritance:
Autosomal Recessive

Severity:
5red

Description:
SCID disorders, which occur in humans, dogs, and mice as well as horses, are characterized by a lack of both humoral and cellular-mediated immunity. In the horse, SCID was first reported in Arabian foals in 1973. In 1980, Perryman and Torbeck showed that SCID in Arabian horses was inherited as an autosomal recessive condition.
The critical defense molecules of the immune system are immunoglobulins and receptors on the T cells. The body normally generates a wide variety of these molecules which then recognize intruders, foreign and potentially hazardous agents such as bacteria and viruses. The specific mutation in SCID resides in one of the critical components of the system, an enzyme called DNA-protein kinase catalytic subunit, DNA-PKcs, which is responsible for the generation of the variety of the immune defense molecules.

Reference:
1. McGuire TC and Poppie MJ. Hypogammaglobulinemia and thymic hypoplasia in horses: A primary combined immunodeficiency disorder. Infection and Immunity 8: 272-277, 1973.
2. Perryman LE and Torbeck RE. Combined immunodeficiency of Arabian horses: confirmation of autosomal recessive mode of inheritance. J Am Vet Med Assoc 76: 1250-1251, 1980.
3. Poppie MJ and McGuire TC. Combined immunodeficiency in foals in Arabian breeding: evaluation of mode of inheritance and estimation of prevalence of affected foals and carrier mares and stallions. J Am Vet Med Assoc 170: 31-33, 1977.
4. Shin EK, Perryman L, Meek K. A kinase negative mutation of DNA-PKcs in equine SCID results in defective coding and signal joint formation. The Journal of Immunology Vol. 158, No. 08 Issue of 04-15-97 pp 3565-3569
5. Studdert MJ. Primary, severe, combined immunodeficiency disease of Arabian foals. Aust Vet J 54: 411-417, 1978.
6. Weiler R, Leber R, Moore BB, VanDyk LF, Perryman LE, Meek K. Equine severe combined immunodeficiency: A defect in V(D)J recombination and DNA-dependent protein kinase activity. Proc Natl Acad Sci USA, 92: 1148-2249.


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Polysaccharide Storage Myopathy

polusacharidosis horses

Category:
Muscular

Mode of Inheritance:
Autosomal Recessive

Severity:
4red

Description:
Equine Polysaccharide Storage Myopathy is a muscle disease most commonly associated with heavy horse breeds. Common heavy horse breeds include the Clydesdale, Shire, Belgian Draft or Belgian, Suffolk Punch and Percheron. EPSM may also occur in the American Quarter Horse and other light horse breeds or draft mules and horses that have draft lineage. The Quarter Horse community calls the condition PSSM (Polysaccharide Storage Myopathy). EPSM may, less commonly, be found in most other breeds including Standardbred, Arab and Thoroughbred.

EPSM is a genetic predisposition to fail to digest grains properly in the horse. The result leads to damage to muscle tissue during exertion. It is estimated by DNA testing that approximately two-thirds of all draft horses have the predisposition for EPSM. A biopsy can determine whether the horse has EPSM.
EPSM can be fatal to affected horses. Symptoms include; Muscle wasting, especially in the rear quarters, Muscle weakness, Gait abnormality, Work intolerance, Poor performance,
Rhabdomyolysis ("Tying Up", Shivers and tremors
Reference:
  • 1. Larcher T, Herszberg B, Molon-Noblot S, Guigand L, Chaffaux S, Guerin G, Cherel Y: Polysaccharide Storage Myopathy in Cob Normand Draft Horses. Veterinary Pathology 2008 , 45:154-158. PubMed Abstract
  • 2.Valberg SJ, Cardinet GH 3rd, Carlson GP, DiMauro S: Polysaccharide storage myopathy associated with recurrent exertional rhabdomyolysis in horses. Neuromuscular Disorders 1992 , 2:351-359. PubMed Abstract
  • 3. Valberg SJ, Macleay JM, Billstrom JA, Hower-Moritz MA, Mickelson JR: Skeletal muscle metabolic response to exercise in horses with 'tying-up' due to polysaccharide storage myopathy. Equine veterinary Journal 1999 , 31:43-47. PubMed Abstract sfx_links.asp
  • 4. Quiroz-Rothe E, Novales M, Aguilera-Tejero E, Rivero JL: Polysaccharide storage myopathy in the M. longissimus lumborum of showjumpers and dressage horses with back pain. Equine veterinary Journal 2002 , 34:171-176. PubMed Abstract
  • 5. Valentine BA, Cooper BJ: Incidence of polysaccharide storage myopathy: necropsy study of 225 horses. Veterinay Pathology 2005 , 42:823-827.
  • 6. McCue ME, Ribeiro WP, Valberg SJ: Prevalence of polysaccharide storage myopathy in horses with neuromuscular disorders. Equine veterinary Journal Supplement 2006 , 36:340-344. PubMed Abstract
  • 7. McCue ME, Valberg SJ: Estimated prevalence of polysaccharide storage myopathy among overtly healthy Quarter Horses in the United States. Journal of American Veterinary Medecine Association 2007 , 231(Sept 1):746-750.
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Cerebellar Abiotrophy



Category:
Neurological

Mode of Inheritance:
Autosomal Recessive

Severity:
3red

Description:
Foals affected with CA appear normal at birth. Around six weeks of age (although sometimes as late as four months), the disease causes the death of neurons in the cerebellum of affected foals, leading to head tremor (intention tremor) and a lack of balance equilibrium (ataxia), among other neurological deficits. Affected horses may show exaggerated action of the forelegs, a wide-based stance, and be unable to rise from a reclining position. They tend to startle easily and often fall due to ataxia. The neurological problems may not be apparent to owners and frequently thought to be a consequence of a fall rather than CA. Symptoms of CA vary in severity. Some foals show very severe symptoms, including the exaggerated gaits and a dramatic lack of balance. Others have little more than the head tremor, which may only manifest itself during goal-directed movement. Regardless of the severity of the symptoms, CA foals are often euthanized or restricted to life as pasture pets, as they are never coordinated enough to be ridden safely. Affected horses are also a danger to themselves because the condition predisposes them to accidents and injury. Veterinarians can perform a series of neurological tests to determine if symptoms are consistent with CA.

Reference:
1. DeBowes RM, Leipold HW, Turner-Beatty M. Equine Cerebellar abiotrophy.Vet Clin North Am Equine Pract. 1987 Aug;3(2):345-52.
2. Gerber H, Gaillard C, Fatzer R, Marti E, Pfistner B, Sustronck B, Ueltschi G, Meier HP, Herholz C, Straub R, Geissbuhler U, Gerber V (1995). "Cerebellar abiotrophy in pure-bred arabians" (in German). Pferdeheilkunde 11: 423–43.

3. Penedo, M. Cecilia T. and Leah Brault. "Progress Toward Identifying the Gene Responsible for Equine Cerebellar Abiotrophy (CA)." Genetics, Research Review, 2006, Center for Equine Health, University of California, Davis. Accessed January 13, 2007
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