by azhefa. » Fri Sep 11, 2020 6:46 am
ββββββββββββββββββββββββββββββββββββββββββββββthese are the different genetic diseases that can be passed on to foals. some are 'sleepers' and only show up after a certain time while others are clear from birth. some of the diseases are also dominant and can affect a horse even if it's heterozygous positive while others are recessive and can be carried as heterozygous positive. these recessive diseases can be very dangerous as the host is unaware and can pass on this disease and possibly breed with another carrier to produce a homozygous foal that shows the disease.
Β© credit to animalgenetics.us for the info
Hyperkalemic Periodic Paralysis Disease (HYPP);
a muscular disease caused by an inherited genetic mutation and has been traced back to one horse named 'impressive' and has the alternative name, 'impressive syndrome', named after this horse. symptoms of HYPP may include muscle twitching, unpredictable paralysis attacks which can lead to sudden death, and respiratory noises. severity of attacks varies from unnoticeable to collapse or sudden death. the cause of death is usually respiratory failure and/or cardiac arrest. this is a dominant disorder and will affect the horse even if heterozygous. only a percentage of quarter horses are affected by this.
Hereditary Equine Regional Dermal Asthenia (HERDA);
also known as hyperelastosis cutis [HC], it's a genetic skin disease predominantly found in the american quarter horse. researchers believe that the origin of this genetic disorder may be the poco bueno's sire line. the symptom of this disorder is a lack of adhesion within the layers of skin due to a genetic defect in the collagen that holds the skin in place. this defect causes the outer layer of skin to split or separate from the deeper layers, sometimes tearing off completely. this is a recessive disorder so only homozygous carriers are affected, but it can be carried as a recessive trait and passed to foals.
Polysaccharide Storage Myopathy (PSSM1);
a dominant autosomal hereditary condition that can cause a genetic form of tying-up with muscle damage and inability to move. one form of PSSM1 is in part a result of a single base pair substitution in GYS1 gene, thereby changing the amino acid sequence of the glycogen synthase enzyme. at least 20 breeds have been identified with type 1 PSSM. the prevalence of the GYS1 mutation in belgians is as much as 50% of and 8% of the quarter horse-related breeds.
Glycogen Branching Enzyme Deficiency (GBED);
a fatal condition caused by the bodies' inability to properly store sugar. this inherited disorder prevents the body from producing the enzyme needed to branch the glycogen structure, preventing the horse from being able to adequately store the sugars. this means that the horse will not be able to store enough energy to fuel important organs, such as the muscles and brain. foals born which are affected by GBED suffer from a range of symptoms associated with this lack of fuel, such as low energy, weakness and difficulty rising. other symptoms include low body temperature, contracted muscles, seizures, and sudden death. unfortunately, GBED is always fatal; most affected foals will die before the age of 8 weeks. GBED often causes the fetus to be aborted in utero. research suggests that as many as 3% of aborted quarter horse foals were homozygous for the GBED mutation. studies show that the mutation responsible for GBED is carried by as many as 10% of quarter horse, paint horse breeds and related breeds. GBED is an autosomal recessive trait, meaning a foal can only be affected if the foal inherits the disease from both parents. horses that are carriers of the GBED have one copy of the mutation but do not have any symptoms associated with the disorder.
Malignant Hyperthermia (MH);
a genetic muscle disorder that affects quarter horses and related breeds. horses with the MH mutation may not show any physical signs of the disorder until triggered by exposure to anesthesia or extreme exercise or stress. symptoms can include high temperature, increased heart rate, high blood pressure, sweating, acidosis, and muscle rigidity. symptoms develop rapidly, and if not treated quickly, this condition can be fatal.
Junctional Epidermolysis Bullosa (JEB1 and JEB2);
an inherited disease also known as Red Foot Disease or Hairless Foal Syndrome. variations of the disorder affect belgian draft horses, american saddlebred horses and relatives of these breeds. this inherited disorder is caused by a mutation that inhibits the body's ability to produce certain proteins responsible for holding the skin onto the body. affected horses are typically born alive with little symptoms. however, after 4 to 5 days of age the foal begins to develop lesions at the pressure points. these lesions quickly grow larger, creating patches all over the foal's body. because the same protein responsible for skin adhesion is also involved in the hoof attachment, the foal also beings to lose the hoof wall and the hoof may detach. oral ulcers are also seen with JEB, as well as foals being born with front teeth. foals often die from infections, or are euthanized within 3-8 days from birth for humane reasons. it is an autosomal recessive trait, meaning a foal can only be affected if the foal inherits the disease from both parents. parents that are carriers do not have any symptoms associated with JEB. however, they can still pass on a copy of the defective gene to their offspring.
Congenital Stationary Night Blindness (CSNB);
a condition making it difficult or even impossible to see in relatively low light. research has now shown that CSNB is a recessive disorder that is directly linked to the leopard complex in appaloosa horses. homozygous positive horses with the leopard complex will have CSNB.
Hoof Wall Separation Disease (HWSD);
a condition that has been identified in connemara ponies and horses that have been crossed with connemara ponies. it is an autosomal recessive disorder that causes the hoof wall to easily break and crack. all four feet will be affected by the disease. damage can be seen in affected ponies as young 2-3 weeks of age. in rare cases some affected ponies develop less severe form of the disease. this is due to the fact that the mutation is not fully penetrant. in very few case the disease can be managed but in other case the ponies must be euthanized. studies estimate that in the general population the percent of horses carrying a single copy of the disorder is around 15%.
Immune Mediated Myositis (IMM);
an incomplete dominant autoimmune disorder which causes muscular atrophy and stiffness in quarter horses. horses with two copies of the mutation associated with IMM are more likely to develop symptoms than horses with a single copy, although environmental factors can play a role. IMM typically affects horses younger than eight years old and older than seventeen years old. IMM episodes typically last several days to several weeks and can be fatal if mismanaged.
Lethal White Syndrome (LWS);
it occurs when a horse inherits two copies of the mutated gene, one from both parents. whereas horses with just one copy of the gene will live normally and exhibit the desirable pattern. a horse with two copies of the mutated gene will suffer intestinal abnormalities caused by undeveloped nerves of the foal's digestive system. these animals die within the first 72 hours of being born and are typically euthanized sooner for humane reasons.
Lavender Foal Syndrome (LFS);
also known as Coat Color Dilution Lethal (CCDL), is a recessive genetic disorder. affected foals often have a difficult delivery, problems standing at birth and usually have episodes where they rigidly extend their limbs, neck and back. These episodes tend to resemble a seizure, although the affected foal does not seem normal between episodes. all affected foals are usually euthanized within days or weeks of birth. studies show that the prevalence of carriers in the Egyptian Arabian population is around 10%. arabian bloodlines are affected.
Squamous Cell Carcinoma (SCC);
the most common cancer affecting the equine eye. at an increased risk of developing this disease are appaloosas, paints, pintos, haο¬ingers, belgians, shires, clydesdales, and any horse lacing pigment in or around the eye.
Severe Combined Immunodeficiency (SCID);
an inherited disease seen in pure and part-bred arab horses. animals with this inherited condition have an enhanced susceptibility to infection and first show signs of disease at between two days and eight weeks of age. clinical diagnosis of the disease is not straightforward as the symptoms, such as raised temperature, respiratory complications and diarrhea, are typical of new-born foals with a range of infections. foals affected by SCID always die from the disorder within the first six months of life. this happens regardless of the level of veterinary care. the disorder is recessive, which means that a horse must be homozygous positive or have two copies of the defective gene to suffer from the disease. consequently both the sire and the dam must possess at least one copy of the mutated gene in order for the offspring to be afflicted.
Cerebellar Abiotrophy (CA);
also referred to as cerebellar cortical abiotrophy (CCA), is a genetic neurological disease in certain species of animals. to date, CA is known to affect breeds of dogs and horses. the disorder manifests itself when Purkinje cells, the neurons that affect balance and coordination, are present in the cerebellum of the brain. horses affected with CA tend to startle easily and often fall. common symptoms include head tremor, a lack of balance and other neurological issues. affected horses may develop a wide-based stance of the forelegs and difficulty rising from a reclining position. in horses, CA is believed to be linked to an autosomal recessive gene. this means that it is not sex-linked and the allele has to be carried and passed on by both parents in order for an affected animal to be born. horses that only carry one copy of the gene may pass it on to their offspring, despite being perfectly healthy themselves and having no symptoms of the disease. because the disorder is recessive, the allele for CA may pass through multiple generations before it is expressed. CA is sometimes confused with Wobbler's syndrome, Equine Protozoal Myeloencephalitis (EPM) and injury-related problems, such as a concussion. it is a condition known to affect arabian horses as well as miniature horses, the gotland pony and possibly the oldenburg. in most cases, foals appear normal at birth, and symptoms generally become noticeable after four months. there have been reported cases where the condition was observed shortly after birth, while others report symptoms developing after the first year.
Occipitoatlantoaxial Malformation (OAAM);
an autosomal recessive developmental skeletal defect which causes compression of the upper cervical cord. this malformation of the occipital bone of the skull results in a neurologic disorder caused when the first two cervical vertebrae (the atlas and axis), fuse to the base of the skull. this structural change creates pressure on the upper portion of the cervical spinal cord, damaging the tissue. the disease may progress with age from mild incoordination and weakness of the limbs to the inability to stand. depending on the severity of the disorder affected foals may be stillborn, show signs at birth or, in some cases, not show signs until a few weeks after birth. diagnosis of the malformed atlas and axis is generally confirmed with radiographs. affected foals are generally euthanized. in order for a foal to be affected, it must inherit a single copy from each parent. horses that have one copy of the mutated gene are not affected but are considered carriers and, if bred, have a 50% chance of passing on the mutated copy to its offspring. additional, yet unidentified, mutations may exist in arabian foals affected with OAAM.
Foal Immunodeficiency Syndrome (FIS);
a recessive genetic disease that primarily affects two relatively rare native UK pony breeds, the dales and the fell pony. FIS is caused by a single mutation in the sodium/myo-inositol cotransporter gene (SLC5A3). this gene plays a vital role in the regulatory response in many tissues including lymphoid tissues. as much as 10% of all fell ponies born each year suffer from FIS. this has put a strain on the long-term survival of this breed as well as the likely spread of FIS into other breeds. most recently animal genetics has found the mutation that causes FIS in approximately 9% of gypsy horse breeds in the US and europe. foals must have two copies of the mutated gene in order to be affected with FIS. therefore, each parent must be a carrier of the mutated gene in order to have an affected foal. affected foals appear healthy and normal at birth but begin to show signs of weakness, dull coat and anorexia at 2-3 weeks. the first clinical signs of this disease include diarrhea, nasal discharge, poor growth, pale gums and decreased appetite. vision may be affected, presumably due to secondary bacterial infections. mortality rate for foal affected by FIS is 100% despite intensive treatment. all FIS affected foals generally die or are euthanized before they reach the age of 3 months. FIS is an autosomal recessive trait, meaning a foal can only be affected if the foal inherits the disease from both parents. parents that are carriers do not have any symptoms associated with FIS.
Hydrocephalus (Friesian Horse);
a developmental disorder involving an accumulation of cerebrospinal fluid within the skull. this often results in foals born prematurely, stillbirth of affected foals and dystocia in dams. in friesian and other horse breeds, hydrocephalus is inherited as an autosomal recessive mode. hydrocephalus is primarily a result of years of inbreeding in the horse population and the widespread use of some influential ancestors. foals can only be affected by hydrocephalus if the foal inherits the disease from both parents. parents that are carriers do not have any symptoms associated with the disorder.
Dwarfism (Friesian Horse);
a genetic condition in friesian horses results in a disproportionate form of dwarfism. this form of dwarfism is characterized by abnormally short limbs while the size of the head and length of back are normal. affected foals also suffer from flexor tendon laxity. unlike normal foals that grow out of this as they mature, horses impacted by this form of dwarfism continue to be impacted by the condition often resulting in an abnormal gait. dwarfism in friesian horses is inherited as a simple autosomal recessive trait. this means that the disorder is not sex linked and all affected foals must inherit two copies of the defective gene (one from each parent). testing shows that roughly 12% of the friesian horse population carriers the mutated gene.
Naked Foal Syndrome (NFS);
it is inherited as a monogenic autosomal recessive trait where a foal can only be affected if the foal inherits the disease from both parents. parents that are carriers do not have any symptoms associated with NSF. horses affected by NFS are born hairless, and often die within days to months after birth. in most cases it is unclear as to the reason for these early deaths. in some rare cases hairless foals have survived up to 2.5 years. the first records of hairless akhal-teke foals date back to 1938, and since then the number of such foals has increased steadily. this disease affects the akhal-teke breed.
Warmblood Fragile Foal Syndrome (WFFS);
n inherited autosomal recessive disorder caused by a single mutation in PLOD1 gene. WFFS has been identified in a population of horses known as warmbloods. warmbloods are a group of mid-sized horse types often called sport horses and developed with the aim of competing in olympic equestrian sports. an affected WFFS foal is born with a two copies of the mutated LHl gene, one coming from each parent. the affected foal will display extreme skin fragility characterized by tearing, ulceration, etc. from contact with normal surroundings. small skin lesions can occur anywhere on the body, but are most noted on pressure points. in addition to skin wounds, lesions may also be found on the gums and other oral cavity mucous membranes. the limb joints are lax and hyperextensible. fetlocks are the most dramatically affected generally preventing a foal from standing normally. unfortunately there is no cure and all affected foals must be euthanized soon after birth.
