Some notes on fatal acquired multiple acyl-CoA dehydrogenase deficiency (MADD) in a two-year-old warmblood stallion and European tar spot (Rhytisma acerinum)

Large-scale study of blood markers in equine atypical myopathy reveals subclinical poisoning and advances in diagnostic and prognostic criteria

Equine atypical myopathy (AM) is a severe rhabdomyolysis syndrome primarily caused by hypoglycin A (HGA) and methylenecyclopropylglycine protoxins. This study aimed to refine diagnostic and prognostic criteria for AM while exploring apparently healthy cograzers. Blood samples from 263 horses, including AM cases (n= 95), cograzers (n= 73), colic horses (n= 19), and controls (n= 76), were analyzed for HGA, its toxic metabolite, and acylcarnitines profile. Diseased horses exhibited alterations in acylcarnitines that strongly distinguished them from controls and colic horses. Regression analyses identified distinct acylcarnitines profiles among groups, with cograzers showing intermediate alterations. Age and gelding status emerged as protective factors against AM. Furthermore, serum acylcarnitines profiling was valuable in predicting AM survival, with isovaleryl-/2-methylbutyrylcarnitine (i.e., C5 acylcarnitine) showing promise as both a diagnostic and prognostic marker. Subclinical alterations in cograzers underscore a novel aspect: the presence of subclinical cases of AM.

Rapid diagnosis of hypoglycin A intoxication in atypical myopathy of horses

Hypoglycin A (2-amino-3-(2-methylidenecyclopropyl)propanoic acid) is the plant toxin shown to cause atypical myopathy in horses. It is converted in vivo to methylenecyclopropyl acetic acid, which is transformed to a coenzyme A ester that subsequently blocks beta oxidation of fatty acids. Methylenecyclopropyl acetic acid is also conjugated with carnitine and glycine. Acute atypical myopathy may be diagnosed by quantifying the conjugates of methylenecyclopropyl acetic acid plus a selection of acyl conjugates in urine and serum. We describe a new mass spectrometric method for sample volumes of <0.5 mL. Samples were extracted with methanol containing 5 different internal standards. Extracts were analyzed by ultra-high-performance liquid chromatography-tandem mass spectrometry focusing on 11 metabolites. The total preparation time for a series of 20 samples was 100 min. Instrument run time was 14 min per sample. For the quantification of carnitine and glycine conjugates of methylenecyclopropyl acetic acid in urine, the coefficients of variation for intraday quantification were 2.9% and 3.0%, respectively. The respective values for interday were 9.3% and 8.0%. Methylenecyclopropyl acetyl carnitine was detected as high as 1.18 µmol/L in serum (median: 0.46 µmol/L) and 1.98 mmol/mol creatinine in urine (median: 0.79 mmol/mol creatinine) of diseased horses, while the glycine derivative accumulated up to 1.97 mmol/mol creatinine in urine but was undetectable in most serum samples. In serum samples from horses with atypical myopathy, the intraday coefficients of variation for C4-C8 carnitines and glycines were ≤4.5%. Measured concentrations exceeded those in healthy horses by ~10 to 1,400 times.