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Genetic Health

Quarter Horse Genetic Health Panel Checker

Enter each parent's panel status and see foal risk per condition.

What this tool does

The AQHA genetic health panel screens for the heritable diseases that run in Quarter Horse and western performance lines. Enter each parent’s status for the seven conditions below and this checker shows the risk to their foals, whether a foal could be affected or a carrier, in plain language, with the correct dominant or recessive model for each disease and what to do about it.

Education, not a diagnosis

This does not test any horse. It estimates risk from the results you enter. Order the actual panel from an accredited lab and consult your veterinarian for management decisions.

HYPP · Hyperkalemic Periodic Paralysis

SCN4A · dominant

A sodium-channel mutation, traced to the stallion Impressive, that causes episodes of muscle trembling, weakness and paralysis. One copy (N/H) can be symptomatic; H/H is more severe.

Test needed

At least one parent has not been tested for HYPP. Test both parents (UC Davis VGL, Etalon, or Animal Genetics) before relying on a risk estimate.

What to do: Because one copy can cause disease, the goal is to breed away from the H allele. Never breed H/H, and avoid N/H × N/H (which risks H/H foals). Affected horses are managed with a low-potassium diet.

HERDA · Hereditary Equine Regional Dermal Asthenia

PPIB · recessive

A recessive collagen defect that makes the skin along the back split, tear and fail to heal, usually surfacing when a horse goes into training. Only homozygotes are affected.

Test needed

At least one parent has not been tested for HERDA. Test both parents (UC Davis VGL, Etalon, or Animal Genetics) before relying on a risk estimate.

What to do: Carriers (N/Hrd) are healthy and can be bred, just never carrier × carrier, which risks 25% affected foals. Breeding a carrier to a tested-clear horse produces no affected foals.

GBED · Glycogen Branching Enzyme Deficiency

GBE1 · recessive · lethal

A recessive, invariably fatal defect in glycogen storage. Affected foals are aborted, stillborn, or weak and die (or are euthanized) within a few months of birth.

Test needed

At least one parent has not been tested for GBED. Test both parents (UC Davis VGL, Etalon, or Animal Genetics) before relying on a risk estimate.

What to do: Never breed carrier × carrier: 25% of such foals are lost. Carriers (N/G) are otherwise normal and safe to breed to a tested-clear mate.

PSSM1 · Type 1 Polysaccharide Storage Myopathy

GYS1 · dominant

A dominant mutation causing abnormal sugar storage in muscle, leading to tying-up, stiffness and muscle damage. A single copy causes the trait; it is worsened by co-inherited MH.

Test needed

At least one parent has not been tested for PSSM1. Test both parents (UC Davis VGL, Etalon, or Animal Genetics) before relying on a risk estimate.

What to do: Select against the allele, any positive horse passes it to about half its foals. Affected horses are managed with a low-starch, high-fat diet and consistent exercise.

MH · Malignant Hyperthermia

RYR1 · dominant

A dominant mutation causing a dangerous rise in body temperature and metabolic crisis under anesthesia, stress or hard work. One copy confers susceptibility, and it aggravates PSSM1.

Test needed

At least one parent has not been tested for MH. Test both parents (UC Davis VGL, Etalon, or Animal Genetics) before relying on a risk estimate.

What to do: Select against it, and critically, flag any positive horse to your veterinarian, anesthesia and stress can trigger a fatal episode that is preventable if known in advance.

MYHM · Myosin-Heavy-Chain Myopathy (IMM)

MYH1 · dominant

The MYH1 (My) variant underlies immune-mediated myositis and non-exertional rhabdomyolysis, rapid topline/muscle wasting, often after an infection or vaccination. N/My can be affected; My/My is more severe. Expression is variable.

Test needed

At least one parent has not been tested for MYHM. Test both parents (UC Davis VGL, Etalon, or Animal Genetics) before relying on a risk estimate.

What to do: Avoid producing My/My, and manage positive horses by minimizing immune triggers. Formerly called the IMM test; UC Davis now reports it as MYHM. It is the 6th panel condition beyond the AQHA 5-panel.

OLWS · Overo Lethal White Syndrome (Frame)

EDNRB · recessive · lethal

The frame-overo (O) allele. One copy (N/O) gives the frame coat pattern and a healthy horse; two copies (O/O) produce an all-white foal that dies of intestinal aganglionosis within days.

Test needed

At least one parent has not been tested for OLWS. Test both parents (UC Davis VGL, Etalon, or Animal Genetics) before relying on a risk estimate.

What to do: Never breed frame carrier × frame carrier, 25% of foals are O/O and lost. Test any frame or minimally-marked horse before pairing it with another possible carrier. Relevant to paint-bred Quarter Horse lines.

How to use it

  1. Find each parent's results. Use the DNA panel results for the stallion and mare (from UC Davis VGL, Etalon, Animal Genetics, or on file with AQHA).
  2. Set the status per condition. For each of the seven conditions, choose Clear, Carrier / one copy, two copies, or Untested for both parents.
  3. Read the foal risk. The checker shows the chance a foal is affected or a carrier, in plain language, with what it means and what to do.

Frequently asked questions

What is the AQHA genetic health panel?

It is a set of DNA tests for heritable diseases in Quarter Horses and related breeds. The classic 5-panel covers HYPP, HERDA, GBED, PSSM1 and MH; the 6-panel adds MYHM (formerly the IMM test). AQHA requires panel results on file for breeding stallions.

What is the difference between a dominant and a recessive condition?

For a dominant condition (HYPP, PSSM1, MH, MYHM) a single copy of the mutation can cause disease, so any positive parent can pass it to about half its foals. For a recessive condition (HERDA, GBED, OLWS) a foal must inherit two copies to be affected; a carrier with one copy is healthy but can pass it on. The checker applies the correct model for each.

Is it safe to breed a carrier?

For recessive conditions, yes, a carrier bred to a tested-clear horse produces no affected foals, though about half will be carriers themselves. The rule is never to breed carrier to carrier, which risks 25% affected foals. For dominant conditions and lethals, the safest path is to select against the allele; this checker spells out the odds for each pairing.

Which conditions are lethal?

GBED and OLWS (overo lethal white) are lethal, affected foals do not survive. That is why carrier-to-carrier pairings for these genes are especially important to avoid. The others range from manageable (HYPP, PSSM1, MYHM with diet and care) to potentially life-threatening under anesthesia or stress (MH).

Does this replace a DNA test?

No. This is education and a risk estimate from the statuses you enter. Order the actual panel from an accredited lab such as the UC Davis Veterinary Genetics Laboratory, then enter each parent's confirmed result. Talk to your veterinarian about managing any positive horse.

Sources

Related: the coat color calculator (which also flags OLWS) and the foaling date calculator.