- Elevated circulating creatine kinase activity (HP:0003236): The activity of creatine kinase in the blood circulation is above the upper limit of normal. Evidence: IEA. (OMIM:612933)
- Juvenile onset (HP:0003621): Onset of signs or symptoms of disease between the age of 5 and 15 years. Evidence: IEA. (OMIM:612933)
- Muscle stiffness (HP:0003552): A condition in which muscles cannot be moved quickly without accompanying pain or spasm. Evidence: IEA. (OMIM:612933)
- Rhabdomyolysis (HP:0003201): Breakdown of muscle fibers that leads to the release of muscle fiber contents (myoglobin) into the bloodstream. Evidence: IEA. (OMIM:612933)
- Increased circulating pyruvate concentration (HP:0003542): The concentration of pyruvate in the blood circulation is above the upper limit of normal. Evidence: IEA. (OMIM:612933)
- Renal insufficiency (HP:0000083): A reduction in the level of performance of the kidneys in areas of function comprising the concentration of urine, removal of wastes, the maintenance of electrolyte balance, homeostasis of blood pressure, and calcium metabolism. Evidence: IEA. (OMIM:612933)
- Rigidity (HP:0002063): Continuous involuntary sustained muscle contraction. When an affected muscle is passively stretched, the degree of resistance remains constant regardless of the rate at which the muscle is stretched. This feature helps to distinguish rigidity from muscle spasticity. Evidence: IEA. (OMIM:612933)
- Increased circulating lactate concentration (HP:0002151): Abnormally increased level of blood lactate (2-hydroxypropanoic acid). Lactate is produced from pyruvate by lactate dehydrogenase during normal metabolism. The terms lactate and lactic acid are often used interchangeably but lactate (the component measured in blood) is strictly a weak base whereas lactic acid is the corresponding acid. Lactic acidosis is often used clinically to describe elevated lactate but should be reserved for cases where there is a corresponding acidosis (pH below 7.35). Evidence: IEA. (OMIM:612933)
- Muscle spasm (HP:0003394): Sudden and involuntary contractions of one or more muscles. Evidence: IEA. (OMIM:612933)
- Myoglobinuria (HP:0002913): Presence of myoglobin in the urine. Evidence: IEA. (OMIM:612933)
- Autosomal recessive inheritance (HP:0000007): A mode of inheritance that is observed for traits related to a gene encoded on one of the autosomes (i.e., the human chromosomes 1-22) in which a trait manifests in individuals with two pathogenic alleles, either homozygotes (two copies of the same mutant allele) or compound heterozygotes (whereby each copy of a gene has a distinct mutant allele). Evidence: IEA. (OMIM:612933)
- Myalgia (HP:0003326): Pain in muscle. Evidence: IEA. (OMIM:612933)
- Exercise intolerance (HP:0003546): A functional motor deficit where individuals whose responses to the challenges of exercise fail to achieve levels considered normal for their age and gender. Evidence: IEA. (OMIM:612933)
These phenotypes are associated with the disease glycogen storage disease due to lactate dehydrogenase M-subunit deficiency (OMIM:612933).