Glycogen storage disease type IV

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Glycogen storage disease type IV (GSD IV) is an inherited disorder caused by the buildup of a complex sugar called glycogen in the body's cells. The accumulated glycogen is structurally abnormal and impairs the function of certain organs and tissues, especially the liver and muscles. There are five types of GSD IV, which are distinguished by their severity, signs, and symptoms.

The fatal perinatal neuromuscular type is the most severe form of GSD IV, with signs developing before birth. Excess fluid may build up around the fetus (polyhydramnios) and in the fetus' body. Affected fetuses have a condition called fetal akinesia deformation sequence, which causes a decrease in fetal movement and can lead to joint stiffness (arthrogryposis) after birth. Infants with the fatal perinatal neuromuscular type of GSD IV have very low muscle tone (severe hypotonia) and muscle wasting (atrophy). These infants usually do not survive past the newborn period due to weakened heart and breathing muscles.

The congenital muscular type of GSD IV is usually not evident before birth but develops in early infancy. Affected infants have severe hypotonia, which affects the muscles needed for breathing. These babies often have dilated cardiomyopathy, which enlarges and weakens the heart (cardiac) muscle, preventing the heart from pumping blood efficiently. Infants with the congenital muscular type of GSD IV typically survive only a few months.

The progressive hepatic type is the most common form of GSD IV. Within the first months of life, affected infants have difficulty gaining weight and growing at the expected rate (faltering weight) and develop an enlarged liver (hepatomegaly). Children with this type develop a form of liver disease called cirrhosis that often is irreversible. High blood pressure in the vein that supplies blood to the liver (portal hypertension) and an abnormal buildup of fluid in the abdominal cavity (ascites) can also occur. By age 1 or 2, affected children develop hypotonia. Children with the progressive hepatic type of GSD IV often die of liver failure in early childhood.

The non-progressive hepatic type of GSD IV has many of the same features as the progressive hepatic type, but the liver disease is not as severe. In the non-progressive hepatic type, hepatomegaly and liver disease are usually evident in early childhood, but affected individuals typically do not develop cirrhosis. People with this type of the disorder can also have hypotonia and muscle weakness (myopathy). Most individuals with this type survive into adulthood, although life expectancy varies depending on the severity of the signs and symptoms.

The childhood neuromuscular type of GSD IV develops in late childhood and is characterized by myopathy and dilated cardiomyopathy. The severity of this type of GSD IV varies greatly; some people have only mild muscle weakness while others have severe cardiomyopathy and die in early adulthood.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the GBE1 gene cause GSD IV. The GBE1 gene provides instructions for making the glycogen branching enzyme. This enzyme is involved in the production of glycogen, which is a major source of stored energy in the body. GBE1 gene mutations that cause GSD IV lead to a shortage (deficiency) of the glycogen branching enzyme. As a result, glycogen is not formed properly. Abnormal glycogen molecules called polyglucosan bodies accumulate in cells, leading to damage and cell death. Polyglucosan bodies accumulate in cells throughout the body, but liver cells and muscle cells are most severely affected in GSD IV. Glycogen accumulation in the liver leads to hepatomegaly and interferes with liver functioning. The inability of muscle cells to break down glycogen for energy leads to muscle weakness and wasting.

Generally, the severity of the disorder is linked to the amount of functional glycogen branching enzyme that is produced. Individuals with the fatal perinatal neuromuscular type tend to produce less than 5 percent of usable enzyme, while those with the childhood neuromuscular type may have around 20 percent of enzyme function. The other types of GSD IV are usually associated with between 5 and 20 percent of working enzyme. These estimates, however, vary among the different types.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

GSD IV is estimated to occur in 1 in 600,000 to 800,000 individuals worldwide. Type IV accounts for roughly 3 percent of all cases of glycogen storage disease.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormal cardiomyocyte morphology · Very frequent (99-80%)

Any structural anomaly of cardiomyocytes, which are terminally differentiated muscle cells in the heart that are interconnected end to end by gap junctions, which allows coordinated contraction of heart tissue.

Abnormal muscle glycogen content · Very frequent (99-80%)

Any anomaly in the amount of glycogen in muscle tissue.

Abnormal neuron branching · Very frequent (99-80%)

Abnormality of the structure and branching of the dendrites of a neuron.

Decreased liver function · Very frequent (99-80%)

Reduced ability of the liver to perform its functions.

Generalized abnormality of skin · Very frequent (99-80%)

An abnormality of the skin that is not localized to any one particular region.

Hepatomegaly · Very frequent (99-80%)

Abnormally increased size of the liver.

Dilated cardiomyopathy · Frequent (79-30%)

Dilated cardiomyopathy (DCM) is defined by the presence of left ventricular dilatation and left ventricular systolic dysfunction in the absence of abnormal loading conditions (hypertension, valve disease) or coronary artery disease sufficient to cause global systolic impairment. Right ventricular dilation and dysfunction may be present but are not necessary for the diagnosis.

Elevated circulating hepatic transaminase concentration · Frequent (79-30%)

Elevations of the levels of SGOT and SGPT in the serum. SGOT (serum glutamic oxaloacetic transaminase) and SGPT (serum glutamic pyruvic transaminase) are transaminases primarily found in the liver and heart and are released into the bloodstream as the result of liver or heart damage. SGOT and SGPT are used clinically mainly as markers of liver damage.

Other findings in the same source

From: Orphanet

Additional reported features include Failure to thrive (Frequent (79-30%)); Generalized hypotonia (Frequent (79-30%)); Hypoalbuminemia (Frequent (79-30%)); Motor delay (Frequent (79-30%)); Myopathy (Frequent (79-30%)); Ascites (Occasional (29-5%)); Cirrhosis (Occasional (29-5%)); Congestive heart failure (Occasional (29-5%)); Esophageal varix (Occasional (29-5%)); Fetal akinesia sequence (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Glycogen storage disease type IV is Metabolic Medicine, with a metabolic specialist / clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with metabolic specialist / clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Is a biochemical or molecular result needed to clarify the diagnosis?
• Does this condition require an individual plan for illness or reduced food intake?
• Should nutrition advice come from a specialist metabolic dietitian?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Glycogen storage disease type IV. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.