Researchers at EquiSeq have developed tests for genetic variants that predispose a horse to Polysaccharide Storage Myopathy type 2 (PSSM2) or Myofibrillar Myopathy (MFM), a subtype of PSSM2. These tests identify horses at risk for developing PSSM2/MFM before they show any symptoms.
A muscle biopsy test shows abnormalities in muscle in PSSM2/MFM and other adult-onset myopathies. A horse that has a negative muscle biopsy result when it is young and relatively free of symptoms may have a positive muscle biopsy result later in life. A genetic test will always give the same result throughout the life of a horse.
No. There are horses with a diagnosis of PSSM2/MFM that do not carry copies of the variants (P2, P3, or P4) identified in these tests. Researchers at EquiSeq are searching for other variants (in different genes) that predispose to PSSM2/MFM.
No. The variants identified in these tests have incomplete penetrance. This means that some horses with one copy of the variants (n/P2, n/P3, or n/P4) will not show any symptoms, even when well past the usual age of onset. Horses with two copies of the variants (P2/P2, P3/P3, or P4/P4) appear to be more strongly affected.
The PSSM2/MFM variants were identified in horses from a group selected for having symptoms of exercise intolerance. Researchers at EquiSeq are working to validate the tests in a large unselected sample before preparing a scientific manuscript for submission to peer-reviewed journals.
EquiSeq cannot disclose the genes associated with a predisposition to PSSM2/MFM prior to publication in a scientific journal.