Molecular characterization of glycogen synthase 1 and its tissue expression profile with type II hexokinase and muscle-type phosphofructokinase in horses

Evaluation of cardiac phenotype in horses with type 1 polysaccharide storage myopathy

BACKGROUND

Type 1 polysaccharide storage myopathy (PSSM1), an equine glycogen storage disorder caused by a gain of function mutation (R309H) in the gene encoding glycogen synthase (GYS1), is associated with the accumulation of amylase-resistant alpha-crystalline polysaccharide inclusions within skeletal muscle. Several glycogenoses in humans have a cardiac phenotype, and reports exist of horses with PSSM and polysaccharide inclusions in cardiac muscle.

HYPOTHESIS/OBJECTIVES

To investigate the hypothesis that horses with PSSM1 display a cardiac phenotype. Our objectives were to compare plasma cardiac troponin I (cTnI) concentration and the incidence of cardiac arrhythmias in PSSM1 homozygotes, heterozygotes, and control horses.

METHODS

One hundred and twenty-five Belgian and Percheron horses under the same management were genotyped for the R309H GYS1 mutation. From these, 8 age-, breed-, and sex-matched cohorts of each genotype were identified. Plasma cTnI concentration and incidence of cardiac arrhythmias (determined by 24-hour Holter ECG) were compared between the groups.

RESULTS

Although some PSSM1-affected horses had mildly increased plasma cTnI concentrations, there was no significant difference in cTnI concentrations between groups. There were no significant differences in the incidence of ectopic beats, cardiac conduction intervals or mean heart rate between groups.

CONCLUSIONS AND CLINICAL IMPORTANCE

We found no evidence of clinically relevant cardiac myocyte injury or arrhythmias in horses with PSSM1. Additional study is required to determine whether myocardial function may be compromised in this disorder.

Molecular cloning and expression of bottlenose dolphin CD34

In terrestrial mammals, the surface molecule CD34 is used as a marker to identify hematopoietic progenitor cells. To clarify whether CD34 expression can be used to confirm the undifferentiated state of hematopoietic-like cells isolated from the bone marrow of bottlenose dolphin, Tursiops truncates, we determined in this study the sequence of dolphin CD34 cDNA and analyzed its mRNA expression. Dolphin CD34 cDNA can be expressed as two forms, one that encodes a full-length version and a variant, truncated version of the gene. Both forms were detected in bone marrow mononuclear cells and in various tissues using RT-PCR. The truncated form was not detected in peripheral blood mononuclear cells, and neither form was detected in polymorphonuclear leukocytes. This is the first report on CD34 in marine mammals and our results suggest that dolphin CD34 may be a useful marker to identify hematopoietic progenitor cells.