Hers Disease

National Organization for Rare Disorders, Inc.

Skip to the navigation


It is possible that the main title of the report Hers Disease is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.


  • Glycogen Storage Disease VI
  • Glycogenosis Type VI
  • Hepatophosphorylase Deficiency Glycogenosis
  • Liver Phosphorylase Deficiency
  • Phosphorylase Deficiency Glycogen Storage Disease

Disorder Subdivisions

  • None

General Discussion

Hers disease is a genetic metabolic disorder caused by a deficiency of the enzyme, liver phosphorylase. This enzyme is necessary to break down (metabolize) glycogen, a carbohydrate that is stored in the liver and muscle and used for energy. Deficiency of this enzyme results in the abnormal accumulation of glycogen in the body. Hers disease is one of a group of disorders known as the glycogen storage disorders. It is characterized by enlargement of the liver (hepatomegaly), moderately low blood sugar (hypoglycemia), elevated levels of acetone and other ketone bodies in the blood (ketosis), and moderate growth retardation. Symptoms are not always evident during childhood, and children are usually able to lead normal lives.


Although symptoms of Hers disease may not be apparent during childhood, some liver enlargement will be present. Many individuals will have no apparent symptoms (asymptomatic). In general, mild to moderately low blood sugar (hypoglycemia) may be present and can cause symptoms of faintness, weakness, hunger, and nervousness. Diminished muscle tone (hypotonia) and mild muscle weakness may occur in some cases.

Growth rate may be slowed, and enlargement of the liver may occur because of an excess accumulation of glycogen. Glycogen is the stored form of energy derived from carbohydrates. In many cases, the body can adapt to low blood sugar levels and is able to produce energy by other means. Therefore, symptoms may go unnoticed for long periods of time.

Liver enlargement often disappears by puberty and final adult height is often normal. Muscle strength and tone is usually normal by adulthood as well.


Hers disease is inherited as an autosomal recessive trait. The disorder is caused by a lack of the enzyme known as liver phosphorylase. Because of this enzyme deficiency, the stored form of energy derived from carbohydrates (glycogen) may accumulate in the liver.

Genetic diseases are determined by two genes, one received from the father and one from the mother. Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%.

Investigators have determined that Hers disease occurs as a result of disruptions or changes (mutations) of the liver glycogen phosphorylase gene (PYGL gene located on the long arm (q) of chromosome 14 (14q21-q22). The PYGL gene encodes for the liver phosphorylase enzyme. Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Pairs of human chromosomes are numbered from 1 through 22, with an additional 23rd pair of sex chromosomes which include one X and one Y chromosome in males and two X chromosomes in females. Each chromosome has a short arm designated "p" and a long arm designated "q". Chromosomes are further subdivided into many bands that are numbered. For example, "chromosome 14q21-q22" refers to bands 21-22 on the long arm of chromosome 14. The numbered bands specify the location of the thousands of genes that are present on each chromosome.

Affected Populations

The incidence of glycogen storage diseases is estimated to be between 1 in 20,000 and 1 in 25,000 persons in the United States. The incidence of Hers disease is unknown, although the disorder has a higher prevalence in the Mennonite population. Symptoms of Hers disease are usually not noticed until adulthood although the disorder may present in childhood.

Standard Therapies


A diagnosis of Hers disease is based on a test for activity of the liver phosphorylase enzyme. A small fragment of liver tissue is surgically removed (biopsy) and assayed for the activity of the enzyme. In persons with Hers disease, this enzyme activity will be reduced.


Because symptoms of Hers disease are generally mild, the disorder usually requires no treatment other than avoidance of prolonged fasting and monitoring by a physician. In individuals experiencing fasting hypoglycemia, a high carbohydrate diet and frequent feedings may be recommended.

Genetic counseling may be of benefit for affected individuals and their families. Other treatment is symptomatic and supportive.

Investigational Therapies

Information on current clinical trials is posted on the Internet at www.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

For information about clinical trials sponsored by private sources, contact:


Dr. Y.T. Chen at Duke University Medical Center, at the request of the Glycogen Storage Disease Association, is collecting DNA from patients with glycogen storage disease type I to form a DNA bank for GSDI. Interested patients may contact the Glycogen Storage Diseases Association for further information. The address and phone number of the organization are listed in the Resources section of this report.



The Merck Manual 17th ed: M. H. Beers and R. Berkow,: eds; Merck Research Laboratories, 1999. Pp. 2387-89.

Cecil Textbook of Medicine, 20th ed.: J. C. Barnett and F. Plum., Eds.: W.B. Saunders Co., 1996. Pp. 1082-83.


Mutations in the Liver Glycogen Phosphorylase Gene (PYGL) Underlying Glycogenesis Type VI. B. Burwinkel et al., Am J Hum Genet. (Apr 1998, 62 (4)). Pp. 785-91.

Identification of a Mutation in Liver Glycogen Phosphorylase in Glycogen Storage Disease VI. S. Chang et al., (May 1998, 7 (5)). Pp. 865-70.

Effect of Clonidine on the Height of a Child with Glycogen Storage Disease Type TYPE VI: A 13 Year Follow-up Study. T. Asami et al., Acta Paediatr Jpn., Oct 1996, 38 (5)). Pp. 524-28.


CLIMB (Children Living with Inherited Metabolic Diseases)

Climb Building

176 Nantwich Road

Crewe, CW2 6BG

United Kingdom

Tel: 4408452412173

Fax: 4408452412174

Email: enquiries@climb.org.uk

Internet: http://www.CLIMB.org.uk

Association for Glycogen Storage Disease

P.O. Box 896

Durant, IA 52747


Tel: (563)514-4022

Fax: (563)514-4022

Email: info@agsdus.org

Internet: http://www.agsdus.org

NIH/National Institute of Diabetes, Digestive & Kidney Diseases

Office of Communications & Public Liaison

Bldg 31, Rm 9A06

31 Center Drive, MSC 2560

Bethesda, MD 20892-2560

Tel: (301)496-3583

Email: NDDIC@info.niddk.nih.gov

Internet: http://www2.niddk.nih.gov/

Association for Glycogen Storage Disease (UK) Ltd

Old Hambledon Racecourse

Sheardley Lane, Droxford

Hampshire, SO32 3QY

United Kingdom

Tel: 03001232790

Email: info@agsd.org.uk

Internet: http://www.agsd.org.uk

Genetic and Rare Diseases (GARD) Information Center

PO Box 8126

Gaithersburg, MD 20898-8126

Tel: (301)251-4925

Fax: (301)251-4911

Tel: (888)205-2311

TDD: (888)205-3223

Internet: http://rarediseases.info.nih.gov/GARD/

Madisons Foundation

PO Box 241956

Los Angeles, CA 90024

Tel: (310)264-0826

Fax: (310)264-4766

Email: getinfo@madisonsfoundation.org

Internet: http://www.madisonsfoundation.org

For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders, Inc.® (NORD). Cigna members can access the complete report by logging into myCigna.com. For non-Cigna members, a copy of the complete report can be obtained for a small fee by visiting the NORD website. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational treatments (if available), and references from medical literature. For a full-text version of this topic, see http://www.rarediseases.org/search/rdblist.html.