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Glycogen Storage Disease Type VI.

Source

GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2020.
2009 Apr 23 [updated 2019 Nov 27].

Author information

1
Connecticut Children’s Medical Center, Hartford, Connecticut
2
University of Connecticut; Connecticut Children’s Medical Center, Hartford, Connecticut

Excerpt

CLINICAL CHARACTERISTICS:

Glycogen storage disease type VI (GSD VI) is a disorder of glycogenolysis caused by deficiency of hepatic glycogen phosphorylase. This critical enzyme catalyzes the rate-limiting step in glycogen degradation, and deficiency of the enzyme in the untreated child is characterized by hepatomegaly, poor growth, ketotic hypoglycemia, elevated hepatic transaminases, hyperlipidemia, and low prealbumin level. GSD VI is usually a relatively mild disorder that presents in infancy and childhood; rare cases of more severe disease manifesting with recurrent hypoglycemia and marked hepatomegaly have been described. More common complications in the setting of suboptimal metabolic control include short stature, delayed puberty, osteopenia, and osteoporosis. Hepatic fibrosis commonly develops in GSD VI, but cirrhosis and hypertrophic cardiomyopathy are rare. Clinical and biochemical abnormalities may decrease with age, but ketosis and hypoglycemia can continue to occur.

DIAGNOSIS/TESTING:

The diagnosis of GSD VI is established in a proband with typical clinical findings and/or biallelic pathogenic variants in PYGL identified by molecular genetic testing.

MANAGEMENT:

Treatment of manifestations: Some individuals with GSD VI may not require any treatment, but treatment with cornstarch and protein improves growth, stamina, and ameliorates biochemical abnormalities including hypoglycemia and ketosis. Even in those with no hypoglycemia, a bedtime dose of cornstarch improves energy and prevents ketosis. Surveillance: Monitoring of blood glucose and blood ketone levels at least several times per month during times of stress including illness, intense activity, periods of rapid growth, or any time at which intake of food is reduced. Annual liver ultrasound examinations should start at age five years. Bone density exam is recommended when puberty is complete. Agents/circumstances to avoid: Excessive amounts of simple sugars; glucagon administration as a rescue therapy for hypoglycemia; growth hormone therapy for short stature; contact sports when hepatomegaly is present. Evaluation of relatives at risk: If the family-specific pathogenic variants are known, it is appropriate to offer molecular genetic testing to at-risk sibs so that early treatment and avoidance of factors that exacerbate disease can be initiated.

GENETIC COUNSELING:

GSD VI is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk relatives and prenatal diagnosis for pregnancies at increased risk are possible if the pathogenic variants in the family are known.

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