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Horse Genetic Testing Explained
Genetic test results appear on many sale listings — here's what each code means, how inheritance works, and what to look for as a buyer or breeder.
Results are reported as two-letter combinations like N/N (two normal copies), N/H (one abnormal copy), or H/H (two abnormal copies). The exact notation varies by test — each guide below explains what the letters mean for that condition.
Hyperkalemic Periodic Paralysis
A dominant muscle disorder linked to the Quarter Horse sire Impressive. Even a single copy causes episodes of weakness and trembling.
Hereditary Equine Regional Dermal Asthenia
A recessive connective tissue disease causing fragile skin. Carriers are healthy; two copies produces a painful, life-limiting condition.
Glycogen Branching Enzyme Deficiency
A recessive lethal disease in Quarter Horse-related breeds. Carrier horses are completely healthy but can produce affected foals.
Polysaccharide Storage Myopathy Type 1
A dominant muscle disorder causing tying-up and muscle pain. Manageable with low-starch diet and consistent exercise.
Malignant Hyperthermia
A recessive mutation that can cause a life-threatening reaction to certain anesthetic agents. Critical to know before any surgical procedure.
Overo Lethal White Syndrome
A Paint Horse mutation where two copies produce foals born with a non-functional gut. Single-copy (Frame Overo) horses are perfectly healthy.
These guides are for general education only. Always consult a veterinarian or equine geneticist before making purchasing or breeding decisions based on genetic results.
Browse horses with genetic test results
Equimeta listings display verified genetic test data directly on the sale ad — no digging required.