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Infantile glycogen storage myopathy in a girl with phosphorylase kinase deficiency
Insights
This study identifies a glycogen storage disorder in a child with hypotonia, caused by a variant form of phosphorylase kinase. This genetic condition may be X-linked recessive, impacting muscle glycogen metabolism.
Area of Science:
- Biochemistry
- Genetics
- Pediatric Neurology
Background:
- Hypotonia in infants can stem from various metabolic myopathies.
- Glycogen storage diseases (GSDs) affect muscle energy metabolism.
- Understanding enzyme deficiencies is crucial for diagnosing neuromuscular disorders.
Observation:
- A 19-month-old girl presented with moderate hypotonia.
- Skeletal muscle analysis revealed excess glycogen accumulation.
- Histochemical and electron microscopy showed abnormal muscle fiber content.
Findings:
- Biochemical assays indicated decreased activity of phosphorylase 'a' and active phosphorylase kinase.
- Total phosphorylase and phosphorylase kinase activities were normal.
- The phosphorylase reaction required 5' AMP activation, suggesting a variant phosphorylase kinase.
Implications:
- The findings suggest a specific variant of phosphorylase kinase causing a glycogen storage myopathy.
- This condition is potentially inherited as an X-linked recessive trait.
- Further research can clarify the genetic basis and therapeutic strategies for this myopathy.
Abstract:
A 19-month-old girl with moderate hypotonia was studied. Histochemical and electronmicroscopic findings revealed that many skeletal muscle fibers contained an excess amount of glycogen. The phosphorylase reaction was normalized only after activation with 5' AMP. Biochemical studies showed an increased glycogen content and decreased activities of phosphorylase "a" and an active form of phosphorylase kinase, whereas activities of total phosphorylase, total phosphorylase kinase, and cyclic AMP-dependent protein kinase were all in the normal range. Thus, phosphorylase kinase in the patient's muscle seemed to be a variant form, which was activated partially under the physiologic condition. This condition may be inherited as an X-linked recessive trait.