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Last updated:
November 12, 2020
Years published: 1987, 1990, 199, 1996, 1998, 2006, 2007, 2020
NORD gratefully acknowledges Tina K. Truong, MMSc, NORD Editorial Intern from the Emory University Genetic Counseling Training Program and Cecelia A. Bellcross, PhD, MS, CGC, Associate Professor, Director, Genetic Counseling Training Program, Emory University School of Medicine, for assistance in the preparation of this report.
Summary
Glycogen storage diseases are a group of diseases where the body’s form of stored energy (glycogen) cannot be broken down into smaller pieces of sugars (glucose) for the body to use. People with glycogen storage disease type 7 (GSD7) usually have symptoms during childhood, but some people may have symptoms beginning as infants or later as adults. GSD7 symptoms are
GSD7 is caused by harmful changes (mutations) in the gene for muscle phosphofructokinase (PFKM) that leads to lowered activity (deficiency) in the phosphofructokinase enzyme, the protein that breaks down glycogen to glucose. The lack of this enzyme leads to a decreased amount of energy available to muscles during exercise. GSD7 is passed down in families in an autosomal recessive pattern of inheritance.
There is no specific cure or treatment for GSD7, but people with GSD7 are recommended to avoid heavy exercise and avoid eating meals with high amounts of carbohydrates.
Introduction
GSD7 was first described by Tarui et al. in 1965 in three Japanese siblings. The siblings were easily tired and were not able to keep pace with other people. They had muscle weakness and stiffness in muscles used in heavy exercise.
There are four types of GSD7:
Childhood (Classic) GSD7
This is the most common form of GSD7 and usually begins in childhood with symptoms including:
Other symptoms can include:
Symptoms usually go away after rest.
Infant GSD7
This rare type of GSD7 occurs in babies. Symptoms include:
Late-onset (adult) GSD7
This form of GSD7 happens in adults who experience only muscle weakness and pain. They may have some muscle weakness and tiredness in childhood.
Hemolytic GSD7
People with hemolytic GSD7 do not have muscle symptoms but have anemia due to break down of red blood cells.
GSD7 is caused by harmful changes (mutations) in the gene for muscle phosphofructokinase (PFKM). This leads to problems with the function of phosphofructokinase enzyme, the protein that breaks down glycogen to glucose. This lowered enzyme activity results in a decreased amount of energy for muscles to use during exercise. This leads to muscle pain and cramps.
GSD7 is inherited in an autosomal recessive manner. Recessive genetic conditions occur when an individual inherits a non-working gene from each parent. If an individual receives one working gene and one non-working gene for the disease, the person will be a carrier for the disease, but will usually not show symptoms. The chance for two carrier parents to both pass the non-working gene and, therefore, have an affected child is 25% with each pregnancy. The chance to have a child who is a carrier, like the parents, is 50% with each pregnancy. The chance for a child to receive working genes from both parents is 25%. The risk is the same for males and females.
GSD7 is a rare disease that is seen more often in individuals of Japanese and Ashkenazi (Eastern European) Jewish ancestry. GSD7 affects males and females in equal numbers. The condition is estimated to occur is less than 1/1,000,000 people.
GSD7 is diagnosed by measuring the amount of the phosphofructokinase enzyme in a sample of muscle tissue taken from a muscle biopsy. It can also be diagnosed by measuring the phosphofructokinase enzyme level in red blood cells.
Lab tests after exercise can also show high levels of other proteins in the blood including creatinine kinase, lactate dehydrogenase, and aspartate transaminase.
Molecular genetic testing from a blood test can confirm changes in the PFKM gene.
The diagnosis of GDS7 is supported by high levels of ammonia and low levels of lactate in muscle biopsy or in blood removed from the forearm before and after exercise (forearm exercise test).
Treatment
Heavy exercise should be avoided to prevent muscle pain and cramps. Eating simple sugars (carbohydrates) should also be avoided because this can make the exercise intolerance worse. Eating high amounts of protein during exercise may prevent symptoms.
Genetic counseling is recommended for individuals with GSD7 and their families.
Information on current clinical trials is posted on the Internet at https://clinicaltrials.gov/ All studies receiving U.S. Government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov
Some current clinical trials also are posted on the following page on the NORD website:
https://rarediseases.org/living-with-a-rare-disease/find-clinical-trials/
For information about clinical trials sponsored by private sources, contact: https://www.centerwatch.com/
For information about clinical trials conducted in Europe, contact: https://www.clinicaltrialsregister.eu/
TEXTBOOKS
Weinstein DA, Koeberl DD and Wolfsdorf JI . Type VII Glycogen Storage Disease. In: The NORD Guide to Rare Disorders, Philadelphia: Lippincott, Williams and Wilkins, 2003:456-7.
Chen Y-T. Glycogen storage diseases. In: Scriver CR, Beaudet AL, Sly WS, et al., eds. The metabolic and molecular basis of inherited diseases. New York: McGraw-Hill, 2001:1521-1551.
JOURNAL ARTICLES
Kanungo S, Wells K, Tribett T, El-Gharbawy A. Glycogen metabolism and glycogen storage disorders. Ann Transl Med. 2018;6(24):474 doi: 10.21037/atm.2018.10.59
Brüser A, Kirchberger J, Schöneberg T. Altered allosteric regulation of muscle 6-phosphofructokinase causes Tarui disease [published correction appears in Biochem Biophys Res Commun. 2013 Feb 8;431(2):367]. Biochem Biophys Res Commun.. 2012;427(1):133-137.
Toscano A, Musumeci O. Tarui disease and distal glycogenoses: clinical and genetic update. Acta Myol. 2007;26(2):105-107.
Ronquist G. Glycogenosis type VII (Tarui’s disease): diagnostic considerations and late sequelae. South Med J. 2002;95(12):1361-1362. doi:10.1097/00007611-200212000-00001
DiMauro S, Bruno C. Glycogen storage diseases of muscle. Curr Opin Neurol. 1998:11:477-484.
INTERNET
McKusick VA, ed. Online Mendelian Inheritance in Man (OMIM). Baltimore, MD: The Johns Hopkins University; Entry No. 232800; Last Update: 09/15/2016. https://www.omim.org/entry/232800 Accessed July 29, 2020.
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