A4: Most important genetic diseases in horses

Question 1

how does genetic disease occur?

Answer 1

Caused by:
a mutation in one gene (monogenic disorder),
by mutations in multiple genes
(multifactorial inheritance disorder),
by a combination of gene mutations and environmental factors,
or by damage to chromosomes (changes in the number or structure of entire chromosomes, the structures that carry genes)

Question 2

List x8
H H H M L E G S

Answer 2

Hemophilia,
LWO,
Melanomas,
HYPP,
SCID,
EPSM,
HERDA,
GBED.
HWSD - autosomal recessive!!!!!!!!

Question 3

Describe Hemophilia disease

Answer 3

Lethal factor, gene mutation,
WW (white) + OO (ovaro white spotting),
Transmitted via X-linked mode if inheritance,
causes prolonged bleeding time in males,
can form hematomas when traumatised.

Question 4

Describe Lethal White Ovaro (LWO)

Answer 4

Also known as Hirschsprung Disease,
autosomal recessive inheritance (TC –> AG mutation in endothelium B receptor gene),
foals born after full gestation appear healthy,
foals have all white coloured coat and blue eyes,
however internally colon is non-functioning, signs of colic develop and homozygous foals die within a few hours.
Seen in American Paint Horses, Pinto, Quarter Horse and TB.
requires molecular diagnosis.

Question 5

Describe Melanomatosis of Grey Horses

Answer 5

Disorder of melanocyte migration,
tumor that results from the abnormal growth of melanocytes/
Occurs in most breeds of grey colour,
Relatively benign melanomas in grey horses of 15+ years,
Around eyes, vagina, anus and on skin, under dock of tail.
tumors can be malignant or benign.
if tumor becomes large it can cause weight loss or colic,
can restrict movement depending on location,
Clinical diagnosis is needed

Question 6

Describe Hyperkalemic Periodic Paralysis (HYPP)

Answer 6

Muscle of affected horse has a point mutation in the Na channel gene.
Autosomal dominant trait in both males + females.
Homozygous horses are affected more than heterozygous.
Na- channel function is disturbed in skeletal muscle.
Can cause: hyperkaliemia,, lameness, muscle weakness, paralysis, muscle twitching + possible death due to cardiac failure.
Occurs mainly in quarter horse, paint & appaloosa breeds,
Molecular genetic diagnosis (DNA test).

Question 7

Describe the Severe Combined Immunodeficiency (SCID)

Answer 7

Frameshift mutation in DNA-dependent protein kinases genes - condition develops when both alleles are mutated.
Autosomal recessive inheritance.
Poor T & B-lymphocyte function = immunodeficiency, death of young foals (1-8 weeks) due to 2 degree infection after colostrum protection ceases.
Occurs in Arab horses (2-25% may be carriers).
Molecular genetic diagnosis

Question 8

Describe Equine Polysaccharides Storage Myopathy (EPSM/PSSM)

Answer 8

Metabolic muscular condition → tying up.
Also related to glycogen storage disorder.
Seen in Quarter horses.
Hereditary Equine Regional D.

Question 9

Describe Hereditary Equine Regional Dermal Asthenia (HERDA)

Answer 9

AKA: Hyper elastosis cutis (HC),
Autosomal recessive,
Collagen defect → layers of skin are not firmly together.

Question 10

Describe Glycogen Branching Enzyme Deficiency (GBED)

Answer 10

No glycogen storage → cardiac & skeletal muscles cannot function = death.
Occurs in foals homozygous for lethal GBED allele.
Diagnosed by DNA blood test.

Question 11

common genetic disease of freisians

Answer 11

dwarfism
autosomal recessive

Question 12

common genetic disease of dales and fell pont

Answer 12

foal immunodeficiency syndrome
autosomal recessive