Type 9 glycogenosis
Glycogenosis refers to a group of metabolic disorders due to the improper metabolism of glycogen. It involves certain enzymes that have become defective or deficient and therefore affected glycogen metabolism. The outcome is the excessive deposition of glycogen in cells. There are different types of glycogenosis and one of them is type 9 glycogenosis. This condition is caused by a deficiency in the enzyme phosphorylase b kinase. The enzyme is essential in the breakdown of glycogen. Without it, the process is interrupted resulting in symptoms characterizing type 9 glycogenosis. Some of the symptoms include hepatomegaly (enlarged liver), hypoglycemia, hyperlipidemia, slowed growth, and lack of muscle tone. The impairment involves both liver and muscle tissues. The deficiency of the enzyme is associated with mutations in PHKA1, PHKA2, PHKB, or PHKG2. These genes code for the subunits of phosphorylase b kinase. Thus, pathological mutation involving any of these genes would impair the function of phosphorylase b kinase and therefore could lead to type 9 glycogenosis.
Depending on the gene involved, type 9 glycogenosis may be inherited as X-linked recessive or autosomal recessive. X-linked inheritance of type 9 glycogenosis is associated with mutations in the PHKA1 or PHKA2 gene. Autosomal recessive inheritance of type 9 glycogenosis involves mutations in PHKB or PHKG2.
- phosphorylase kinase (PHK) deficiency
- glycogen storage disease type VII (GSD VII)