Glycogen Storage Disease Type VII, or GSD VII, is a genetic disorder where the body cannot break down stored sugar called glycogen properly. This causes glycogen to accumulate in muscles, leading to various issues.

People with GSD VII experience muscle cramps, struggle with exercise, and may have muscle breakdown, which can harm kidneys. Additionally, they might develop a type of anemia caused by abnormal breakdown of red blood cells. There are four known types of GSD VII:

  • Classical Form: This is the most common type and involves muscle cramps, pain, and difficulty with exercise. Some individuals might feel sick after intense physical activity. A heart condition called hypertrophic cardiomyopathy can also occur, though it’s not common.
  • Severe Infantile Form: Infants with this rare form have weak muscles, heart and breathing issues, joint problems, and may develop cataracts. Sadly, they often do not survive beyond early childhood and could have intellectual disabilities.
  • Late-Onset Form: In this type, muscle cramps and exercise difficulties appear later in life, sometimes starting in childhood.
  • Hemolytic Form: This form causes anemia without muscle symptoms.

Currently, there’s no cure for GSD VII. Individuals with this condition must be cautious about exercising too much, as it can cause muscle breakdown and kidney problems. Managing exercise frequency and intensity is essential to maintain their health.

GSD VII is caused by pathogenic (disease-causing) variants in the PFKM gene and exhibits autosomal recessive inheritance. This means that both parents must be carriers to have a 25% chance to have a child with the condition. The risk of being a carrier is based on a person’s ancestry or ethnic background. For example, individuals of Ashkenazi Jewish descent have a 1 in 250 chance to be a carrier. 

Other names for this condition are glycogenosis 7, muscle phosphofructokinase deficiency, PFKM deficiency, phosphofructokinase deficiency, and Tarui disease.

Resources:  

Association for Glycogen Storage Disease

Medline Plus

Revised October 2023