Muscle phosphorylase kinase deficiency: a neutral metabolic variant or a disease?

TY - JOUR

T1 - Muscle phosphorylase kinase deficiency

T2 - a neutral metabolic variant or a disease?

AU - Preisler, N

AU - Orngreen, M C

AU - Echaniz-Laguna, A

AU - Laforet, P

AU - Lonsdorfer-Wolf, E

AU - Doutreleau, S

AU - Geny, B

AU - Akman, H O

AU - Dimauro, S

AU - Vissing, J

PY - 2012/1/24

Y1 - 2012/1/24

N2 - Objective: To examine metabolism during exercise in 2 patients with muscle phosphorylase kinase (PHK) deficiency and to further define the phenotype of this rare glycogen storage disease (GSD). Methods: Patient 1 (39 years old) had mild exercise-induced forearm pain, and EMG showed a myopathic pattern. Patient 2 (69 years old) had raised levels of creatine kinase (CK) for more than 6 months after statin treatment. Both patients had increased glycogen levels in muscle and PHK activity <11% of normal. Two novel pathogenic nonsense mutations were found in the PHKA1 gene. The metabolic response to anaerobic forearm exercise and aerobic cycle exercise was studied in the patients and 5 healthy subjects. Results: Ischemic exercise showed a normal 5-fold increase in plasma lactate (peak 5.7 and 6.9 mmol/L) but an exaggerated 5-fold increase in ammonia (peak 197 and 171 μmol/L; control peak range 60-113 μmol/L). An incremental exercise test to exhaustion revealed a blunted lactate response (5.4 and 4.8 mmol/L) vs that for control subjects (9.6 mmol/L; range 7.1-14.3 mmol/L). Fat and carbohydrate oxidation rates at 70% of peak oxygen consumption were normal. None of the patients developed a second wind phenomenon or improved their work capacity with an IV glucose infusion. Conclusion: Our findings demonstrate that muscle PHK deficiency may present as an almost asymptomatic condition, despite a mild impairment of muscle glycogenolysis, raised CK levels, and glycogen accumulation in muscle. The relative preservation of glycogenolysis is probably explained by an alternative activation of myophosphorylase by AMP and Pi at high exercise intensities.

AB - Objective: To examine metabolism during exercise in 2 patients with muscle phosphorylase kinase (PHK) deficiency and to further define the phenotype of this rare glycogen storage disease (GSD). Methods: Patient 1 (39 years old) had mild exercise-induced forearm pain, and EMG showed a myopathic pattern. Patient 2 (69 years old) had raised levels of creatine kinase (CK) for more than 6 months after statin treatment. Both patients had increased glycogen levels in muscle and PHK activity <11% of normal. Two novel pathogenic nonsense mutations were found in the PHKA1 gene. The metabolic response to anaerobic forearm exercise and aerobic cycle exercise was studied in the patients and 5 healthy subjects. Results: Ischemic exercise showed a normal 5-fold increase in plasma lactate (peak 5.7 and 6.9 mmol/L) but an exaggerated 5-fold increase in ammonia (peak 197 and 171 μmol/L; control peak range 60-113 μmol/L). An incremental exercise test to exhaustion revealed a blunted lactate response (5.4 and 4.8 mmol/L) vs that for control subjects (9.6 mmol/L; range 7.1-14.3 mmol/L). Fat and carbohydrate oxidation rates at 70% of peak oxygen consumption were normal. None of the patients developed a second wind phenomenon or improved their work capacity with an IV glucose infusion. Conclusion: Our findings demonstrate that muscle PHK deficiency may present as an almost asymptomatic condition, despite a mild impairment of muscle glycogenolysis, raised CK levels, and glycogen accumulation in muscle. The relative preservation of glycogenolysis is probably explained by an alternative activation of myophosphorylase by AMP and Pi at high exercise intensities.

U2 - 10.1212/wnl.0b013e31824365f9

DO - 10.1212/wnl.0b013e31824365f9

M3 - Journal article

C2 - 22238410

SN - 0028-3878

VL - 78

SP - 265

EP - 268

JO - Neurology

JF - Neurology

IS - 4

ER -