Genetic Disorders

Question 1

what disorders are common in arabians

Answer 1

• severe combined immunodeficiency
• cerebellar abiotrophy
• lavender foal syndrome

Question 2

what are common disorders for friesian

Answer 2

• dwarfism
• hydrocephalus

Question 3

what are common disorders are there for belgian american saddlebred

Answer 3

• junctional epidermolysis bullosa

Question 4

what is common in paint

Answer 4

• overo lethal white foal syndrome

Question 5

what is common in rocky mountian horses

Answer 5

• multiple congenital ocular anomalies

Question 6

what is common in appaloosa

Answer 6

• congenital stationary night blindness

Question 7

what is common in quater horses

Answer 7

• glycogen branching ezymes disorders

Question 8

what is common in warmbloods

Answer 8

• warmbloof fragile foal syndrome

Question 9

indications that a condition might have a genetic aetiology

Answer 9

1. occurrence restricted to a single breed or related breeds ( in some cases, this disorder may affect only some horses within a particular breed, with the affected horses carrying a common phenotype. This is seen in the case of OLWFS, MCOA,CSNB, and LFS which occur in occur in conjuction with particular colour genotypes)
2. common ancestor ( HYPP and impressive, hereditary equine regional dermal asthenia and the stallion poco bueno GBED and the stallion king P- 234) = as with occurence within a breed, possibility of common usage and environmental factors must be taken into account when looking at a common ancestor
3. underlying biochemical aetiology ( PSSM, GBED/GSD)
4. similar disorder with known genetic basis occurs in other species ( SCID, dwarfism, polydactyly and HERDA)

Question 10

what is HERDA

Answer 10

• hereditary equine regional dermal arthenia - stock horses affected
• also called hyperelastosis cutis (HC)
• presents as skin peeling off, particularly over the shoulders and along the dorsal midline
• usually appears during training
• affected horses are typically euthanized although it is possible to extend lifespans of minimally affected horses if they are kept indoors and not subjected to any sort of physical trauma
• due to a missense mutation in the cyclophilin B gene (PPIB) that regulates the three dimensional structure of collagen; which is essential for dermal integrity
• mutation has been traced by a single stallion, POCO bueno (1944-1969)
• first identified as a genetic disorder in 1971, causative mutation identified in 2007

Question 11

what is JEB

Answer 11

• junctional epidermolysis bullosa ( draft horses, especially belgians, and ameriacan saddlebreds affected)
• presents as extensive erosive ulcerative lesions on distal extremities, lips, and over joints; skin and hooves slough off
• two breed - specific mutations have been identified : frameshift in LAMC2 in draft breeds causing pre mature stop codons and a large deletion in LAMA3 (american saddlebreed) - genocopies
• these genes code for laminitis, involved in connecting epidermal and dermal layers of the skin
• affected foals die or are euthenized

Question 12

what is GBED

Answer 12

• glycogen branching enzyme disorder (also glycogen storage disorder) - effects stock horses
• presents as hypoglycemic seizures, progressive muscle weakness, respiratory failures and sudden death; also identified as cause of late-term abortions
• caused by nonsense mutation in glycogen branching enzyme 1 (GBE1) that disrupts glycogen metabolism
• traced to King P-234 (1932-1958)

Question 13

what is OLWFS

Answer 13

• overo lethal white foal syndrome (paint/stock horses affected)
• presents as ileocolonic aganglionosis creating a fatal colic
• caused by a missence mutation in the endothelin B receptor gene (EDNRB) that regulates development of neural crest cells into enteric ganglia and melanocytes

Question 14

What is Dominant white

Answer 14

• characteristic of camarillo white, franches montagne and american white horses
• sporatic appearance in thoroughbreds, american quarter horses, icelandic horses shetland ponies and arabian horses
• characterized by phenotypic and allelic heterogeneity with the conidtion resulting from 27 mutations identified in the KIT gene that stimulates signaling pathways for cell growth, division, survival and migration
• some of the alleles are embryonic lethals; some combinations of alleles create heterozygous lethality

Question 15

what is LFS

Answer 15

• lavender foal syndrome - arabian horses effected
• also called coat colour dilution lethal (CCDL)
• neonates present with neurological abnormalitites such as tetanic seizures, recumbency and inability to stand along with a pale pink or lavender coat colour
• causation mutation is a deletion in the myosin V gene (MYO5A) that creates a premature stop codon; myosin Va is involved in organelle transport and membrane trafficking in brain and skin

Question 16

what is SCID

Answer 16

• severe combined immunodeficiency - Arabian horses affected
• affected foals lack the ability to create antibodies and typically succumb to infectious disease after passive immnity acquired from the dam ceases to be effective
• causative mutation is frameshift in DNA - dependent protein kinases (DNA PKcs) that play a cruicial role in formation in antibodies

Question 17

what is FIS

Answer 17

• fatal immunodeficiency syndrome (fell and dale ponies effected) - also identified in gypsy vanner horses
• fell pony syndrome
• genocopy of SCID
• immunocomprimised foals succumb to disease after passively aquired antibiodies cease to provide effective protection
• causative mutation is missense mutation in sodium/ myosin -ninositol transporter (SLC5A3) necessary for erythropoiesis and formation of B and T lymphocytes

Question 18

what is hydrocephalus

Answer 18

• friesian horses affected
• presents as an accumulation of cerebrospinal fluid within the ventricle system of the brain that results in pre-natal or neonatal death
• causative mutation in nonsense mutation ( B3GALNT2)

Question 19

what is NFS

Answer 19

• naked foal syndrome (also hairless or hairlessness
• akhal teke horses affected
• caused by a nonsense mutation in the suppression of tumorigenicity 14 (ST14) gene that is essential for development of hair follicles
• affected foals are usually euthenized although horses have been kept alive for as long as 5 years
• no sun exposure and vitamine D suppliment provided

Question 20

what is WFFS

Answer 20

• warmblood fragile foal syndrome
• warmblood breeds effected mostly
• presents as neonates with fragile skin, lacerations of the mucous membranes, hyperextensible joints ; affected foals usually die or are euthenized shortly after birth - may be aborted
• causative mutation is missense mutation in procollagen - lysine PLOD1 that is involved in crosslinking collagen molecules

Question 21

what is HYPP

Answer 21

• Hyperkalemic periodic paralysis (stock horses effected)
• impressive syndrome
• presents as muscle fasciculations, swaying and staggering that may progress to collapse and flaccid recumbancy ; horses can suffer laryngeal collapse and cardiac arrest
• the phenotype of heterozygotes ranges from very midly or virtually unnoticeable to extremely effected ; due to an autosomal incompletely dominant mutaition
• traced back to impressive 1969-1995 identified 1992

Question 22

what is PSSM1

Answer 22

• polysaccharide storage myopathy
• confers susceptibility to exertional rhabdomyolysis
• autosomal dominant mode of inheritance
• horses identified as having the mutation can be managed to reduced incidence and severity of episodes of exertional rhabdomyyolysis

Question 23

what is CA

Answer 23

• cerebellar abiotrophy - affects arabians and related breeds
• autosomal recessive mode of inheritance
• neurodegenerative disorder that manifests dats to months after birth as uncoordinated limb movement, head tremours and difficulty standing

Question 24

what is dwarfisms

Answer 24

• friesians, miniature horses, shetland ponies
• mutation causing dwarfism in breed specific
• all mutations thus far have identified are autosomal recessive
• the different mutations in Friedan horses, miiature horses and shetland ponies are genocopies

Question 25

what is hoof wall separation

Answer 25

• affects connemara ponies
• autosomal recessive mode of inheritance

Question 26

what is congenital lordosis

Answer 26

• affects american saddlbreds
• lordosis may result from degeneration as a result of aging (phenocopy) or the presence of an autosomal recessive mutation in homozygous state
• the presence of major gene has been implicated but the causative mutation has not been identified

Question 27

what is DSLD

Answer 27

• degenerative suspensory ligament desmitis
• affects peruvian pasos and paso finos
• multiple genes implecated as conferring suscptability

Question 28

what is brachygnathism

Answer 28

• parrot mouth

Question 29

what is cryporchidims

Answer 29

• retained testicles
• polygenic inheritance determined in other species