Understanding
the 5-panel Genetics
| The 5-panel is a test for
five different genetic diseases found in quarter horses and other stock
horse breeds. The diseases tested for in the 5-panel are HERDA, GBED, HYPP,PSSM1,
and MH. Starting in 2014 any AQHA stallion breeding 25 or more mares must
be 5-panel tested through AQHA/UC Davis before their 2015 foals can be
registered. Starting in 2015 ALL AQHA stallions must be 5-panel tested
before their 2016 foals can be registered.
While HERDA and GBED are
recessive disorders and a carrier horse will be as normal as any other
horse, PSSM1, HYPP, and MH are dominant disorders and a horse that carries
only one copy can show symptoms of the disease. Thus testing N/N for PSSM1,
HYPP, and MH should be a must while HERDA and GBED can be managed with
responsible breeding (testing stallion and mare and never breed a carrier
to a carrier). |
| HERDA |
Hereditary Equine Regional
Dermal Asthenia. Also known as Hyperelastosis Cutis, HC is a genetic skin
disease predominantly found in the American Quarter Horse.
This disease is traced back
to Poco Bueno and King, thus found in Cutting/Working Cow bred horses that
go back to these stallions. Famous carriers are horses like Doc O'Lena,
Smart Little Lena, High Brow Cat and many of their offspring.
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. Areas under the saddle seem to be most prone
to these lesions, often leaving permanent scars and preventing the horse
from being ridden.
The disorder is recessive,
which means that a horse must 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. Offspring
born with one copy of the defective gene and one non-defective copy are
considered a carrier and have a 50% chance of passing the defective gene
on, but are in no way affected by carrying the gene. They are just like
any other horse. |
| HERDA N/N |
Horse tested negative for
the gene mutation that causes HERDA and will not pass on the defective
gene to its offspring |
| HERDA Hrd/N |
Both the normal and mutant
copies of the gene detected. Horse is a carrier for the HERDA mutation
and can pass on a copy of the defective gene to its offspring 50% of the
time. A carrier does not show symptoms of the disease. |
| HERDA Hrd/Hrd |
The horse carries two copies
of the HERDA mutation and is homozygous for HERDA. The horse is affected
with the HERDA genetic disorder. |
| note |
HERDA is found predominately
in cutting / working cow horse bred horses, for two reasons: it does go
back to cutting champion Poco Bueno, a bloodline found in most cutting
bred horses, and it is rumored that a carrier horse does have more flexible
tendons than a non-carrier, thus some breeders not only tolerate a carrier
but specifically look for one. Because a carrier is a healthy horse and
produces healthy offspring if not bred to another carrier, this may be
a good practice to keep the gene pool more diversified.
It is said that 90% of NCHA
performers with $400K+ earnings are carriers. |
| GBED |
Glycogen Branching Enzyme
Deficiency (GBED) is a fatal condition caused by the bodies' inability
to properly store sugar. In a normal horse, the body stores sugar as energy
by converting glucose to glycogen. 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 foetus 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. |
| GBED N/N |
Horse tested negative for
the gene mutation that causes GBED and will not pass on the defective gene
to its offspring. |
| GBED N/Gb |
Both the normal and mutant
copies of the gene detected. Horse is a carrier for the GBED mutation,
and can pass on a copy of the defective gene to its offspring 50% of the
time. A carrier does not show symptoms of the disease. |
| GBED Gb/Gb |
The horse carries two copies
of the GBED mutation and is homozygous for GBED. The horse is affected
with the GBED genetic disorder. |
| HYPP |
Equine Hyperkalemic Periodic
Paralysis Disease (HYPP) is a muscular disease caused by an inherited genetic
mutation. HYPP 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.
HYPP is a dominant disorder
meaning both homozygous positive (HH) and heterozygous (nH) horses will
be affected. Only homozygous negative (nn) horses are not affected
by HYPP. If a horse tests HYPP positive, he has the disease and should
not be bred. |
| HYPP N/N |
Horse tested negative for
the gene mutation that causes HYPP and will not pass on the defective gene
to its offspring |
| HYPP H/N |
Both the normal and HYPP
alleles were detected. Horse tested heterozygous for HYPP. The horse is
affected with the HYPP genetic disorder and there is a 50% chance this
horse will pass a HYPP allele to its offspring. |
| HYPP H/H |
Positive for dominant HYPP
gene, indicates the animal carries two inherited copies. Homozygous HYPP
horses are genetically bound to pass the gene to 100% of their progeny
when bred and all foals will be HYPP horses. AQHA no longer allows the
registration of HYPP H/H horses. |
| note |
HYPP is found predominately
in halter bred horses, for two reasons: it does go back to halter champion
Impressive, a bloodline found in most halter bred horses, and it seems
as if a carrier horse does have better (thicker) muscleing than a non-carrier,
thus breeders tolerate the disease and do not cull carriers. |
| PSSM |
Polysaccharide Storage Myopathy
or PSSM (PSSM1) is an inherited muscle disease that affects many and diverse
breeds of horses. The clinical characteristics of PSSM vary between breeds,
from muscle pain, cramping and cell damage with exercise, to progressive
muscle atrophy.
There are no "carriers"
of PSSM. PSSM is a dominant disorder. Which means a horse only has to carry
one copy of the disease to be affected. If the horse tests PSSM positive,
he has the disease and should not be bred. |
| PSSM N/N |
Horse tested negative for
PSSM and does not carry the PSSM gene mutations. The horse will not pass
on the defective mutations to its offspring. |
| PSSM P1/N |
Both the normal and PSSM
alleles were detected. Horse tested heterozygous for PSSM. The horse is
affected with the PSSM genetic disorder and there is a 50% chance that
this horse will pass a PSSM allele to its offspring. |
| PSSM P1/P1 |
Positive for the dominant
PSSM gene mutations, indicates the animal carries two inherited copies.
Homozygous PSSM horses are genetically bound to pass the gene to 100% of
their progeny when bred meaning all foals will be have at least one copy
of the dominant PSSM gene mutation. |
| MH |
Malignant Hyperthermia or
MH is 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.
MH is inherited as an autosomal
dominant trait, so the disorder can be passed on even if only one parent
has the defective gene. The mutation can be present along with PSSM and
if a horse also has PSSM, the symptoms associated with MH can be more severe.
Therefore, testing for both PSSM and MH is recommended for Quarter Horse
breeds.
Although this condition
is rare, testing for MH is recommended in case a horse must undergo anesthesia.
Horses that are known to have the MH mutation can be given medication prior
to administering anesthesia to help reduce the severity of the symptoms.
MH is another dominant disorder and horses testing positve for it should
not be bred. |
| MH N/N |
Horse tested negative for
MH and does not carry the MH gene mutation. The horse will not pass on
the defective gene to its offspring. |
| MH N/MH |
Both the normal and MH alleles
were detected. Horse tested heterozygous for MH. The horse is affected
with the MH disorder and there is a 50% chance this horse will pass a MH
allele to its offspring. |
| MH MH/MH |
Positive for dominant MH
mutation, indicates the animal carries two inherited copies. Homozygous
MH horses are genetically bound to pass the gene to 100% of their progeny
when bred and all foals will be MH horses. |
This article was in part
copied from www.animalgenetics.us and relieved of some of the more scientific
explanations to make it easier to understand. Please refer to their original
article online.
And we are still learning
more about these diseases. |
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