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Condition report · Metabolic

Glycogen Storage Disease

Whole genome sequencing distinguishes GSD type Ia (G6PC) from type Ib (SLC37A4). This distinction is critical because type Ib patients develop neutropenia treatable with empagliflozin, a repurposed SGLT2 inhibitor that has transformed type Ib management.

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About this condition

A group of rare genetic metabolic disorders caused by enzyme deficiencies that affect the body's ability to store or break down glycogen, leading to its abnormal accumulation in various tissues like the liver and muscles, and resulting in a range of health issues.

Glycogen storage disease type I (GSD-I, von Gierke disease) is an autosomal recessive disorder of glucose metabolism caused by deficiency of either glucose-6-phosphatase-α (type Ia, G6PC gene, chromosome 17q21.31, ~80% of cases) or the glucose-6-phosphate translocase (type Ib, SLC37A4 gene, chromosome 11q23.3, ~20%). Both subtypes prevent the final step of hepatic glycogenolysis and gluconeogenesis (the dephosphorylation of glucose-6-phosphate to free glucose), causing severe fasting hypoglycemia, hepatomegaly, hyperlipidemia, hyperuricemia, and lactic acidosis. GSD-I affects approximately 1 in 100,000 births.

GSD-I presents in infancy with hepatomegaly (massive glycogen accumulation), severe fasting hypoglycemia (symptomatic within 3-4 hours of fasting), lactic acidosis, hyperlipidemia (triglycerides often >1,000 mg/dL), and hyperuricemia. Long-term complications include hepatic adenomas (developing in 50-75% of patients by adulthood, with malignant transformation risk), gout, nephrolithiasis, progressive renal disease, and osteoporosis. Dietary management prevents hypoglycemia and reduces metabolic derangements. It relies on a continuous glucose supply through frequent meals, uncooked cornstarch (which provides sustained glucose release), and nocturnal gastric drip feeding.

The critical phenotypic distinction between types Ia and Ib is that type Ib patients develop neutropenia and neutrophil dysfunction, causing recurrent bacterial infections, oral ulcers, and inflammatory bowel disease (IBD-like), in addition to the metabolic phenotype shared with type Ia. Empagliflozin, an SGLT2 inhibitor repurposed from diabetes treatment, has dramatically improved neutropenia and IBD symptoms in GSD type Ib by reducing intracellular glucose-6-phosphate accumulation in neutrophils. This gene-specific therapy makes molecular genotyping essential: type Ia patients do not develop neutropenia and do not benefit from empagliflozin.

Empagliflozin, a diabetes drug repurposed for GSD type Ib, has transformed management of the neutropenia and IBD-like colitis that type Ib patients develop. This therapy is only indicated for type Ib (SLC37A4), not type Ia (G6PC).

The 13 conditions we analyse

Glycogen Storage Disease Type I

Autosomal recessive

Caused by variants in G6PC1 (type Ia) or SLC37A4 (type Ib), which cause low blood sugar between meals, an enlarged liver and, in type Ib, low neutrophil counts and infections.

What a diagnosis changes

Knowing allows frequent feeds with slow-release starch, and in type Ib treatment of neutropenia, which prevents dangerous low blood sugar.

Genes analysed

Also known as

G6P deficiency; glycogen storage disease due to G6P deficiency; glycogen storage disease due to glucose-6-phosphatase deficiency; glycogen storage disease type 1; glycogenosis type 1; glycogenosis type I; GSD due to G6P deficiency; GSD type 1; GSD type I; GSD1; hepatorenal glycogenosis; von Gierke disease; von Gierke's disease

Specific forms also covered

  • Glycogen Storage Disease Due To Glucose-6-Phosphatase Deficiency Type Ia

    Autosomal recessive

    Glycogenosis due to glucose-6-phosphatase deficiency (G6P) type a, or glycogen storage disease (GSD) type 1a, is a type of glycogenosis due to G6P deficiency.

    G6PC1

Includes 4 related subtypes ↓
  • glycogen storage disease due to glucose-6-phosphatase deficiency type IA
  • glycogen storage disease Ib
  • glycogen storage disease Id
  • glycogen storage disease type 1 due to SLC37A4 mutation
MONDO:0002413Orphanet 364MedGen 6640

Glycogen Storage Disease Type III

Autosomal recessive

Caused by variants in AGL, which cause low blood sugar, an enlarged liver and, in many people, muscle and heart muscle weakness.

What a diagnosis changes

Knowing allows a high-protein diet with regular feeds and monitoring of liver, heart and muscles.

Genes analysed

Also known as

AGL glycogen storage disease; amylo-1,6-glucosidase deficiency; Cori disease; Cori-Forbes disease; Forbes disease; GDE deficiency; glycogen storage disease caused by mutation in AGL; glycogen storage disease type 3; glycogenosis due to glycogen debranching enzyme deficiency; glycogenosis type 3; glycogenosis type III; GSD due to glycogen debranching enzyme deficiency; GSD type 3; GSD3; GSDIII; limit dextrinosis

MONDO:0009291OMIM 232400Orphanet 366MedGen 6641

Glycogen Storage Disease Type IV

Autosomal recessive

Caused by variants in GBE1, ranging from progressive liver disease in childhood to adult polyglucosan body disease affecting nerves and bladder.

What a diagnosis changes

Knowing guides liver and neurological monitoring and, in severe liver forms, transplant planning.

Genes analysed

Also known as

amylopectinosis; Andersen disease; Andersen Disease (GSD IV); Andersen's disease; GBE1 glycogen storage disease; glycogen storage disease caused by mutation in GBE1; glycogen storage disease IV; glycogen storage disease type 4; glycogenosis due to glycogen branching enzyme deficiency; glycogenosis type 4; glycogenosis type IV; GSD due to glycogen branching enzyme deficiency; GSD IV; GSD type 4; GSD type IV; GSD4

Includes 8 related subtypes ↓
  • adult polyglucosan body disease
  • glycogen storage disease due to glycogen branching enzyme deficiency, adult neuromuscular form
  • glycogen storage disease due to glycogen branching enzyme deficiency, childhood combined hepatic and myopathic form
  • glycogen storage disease due to glycogen branching enzyme deficiency, childhood neuromuscular form
  • glycogen storage disease due to glycogen branching enzyme deficiency, congenital neuromuscular form
  • glycogen storage disease due to glycogen branching enzyme deficiency, fatal perinatal neuromuscular form
  • glycogen storage disease due to glycogen branching enzyme deficiency, non progressive hepatic form
  • glycogen storage disease due to glycogen branching enzyme deficiency, progressive hepatic form
MONDO:0009292OMIM 232500Orphanet 367MedGen 6642

Glycogen Storage Disease Type VI

Autosomal recessive

Caused by variants in PYGL, which usually cause an enlarged liver and mild low blood sugar during fasting in childhood.

What a diagnosis changes

Knowing allows avoidance of prolonged fasting and dietary management.

Genes analysed

Also known as

glycogen storage disease 6; glycogen storage disease caused by mutation in PYGL; glycogen storage disease type 6; glycogenosis due to liver glycogen phosphorylase deficiency; glycogenosis type 6; glycogenosis type VI; GSD due to liver glycogen phosphorylase deficiency; GSD type 6; GSD type VI; GSD6; hepatic glycogen phosphorylase deficiency; hepatic phosphorylase deficiency; hers disease; liver glycogen phosphorylase deficiency; PYGL glycogen storage disease

MONDO:0009294OMIM 232700Orphanet 369MedGen 6643

Glycogen Storage Disease Type IX

Caused by variants in PHKA2, PHKB, PHKG2 or PHKA1, which can cause an enlarged liver, low blood sugar during fasting or, in the PHKA1 form, exercise-related muscle symptoms.

What a diagnosis changes

Knowing allows avoidance of prolonged fasting, dietary management and liver monitoring, especially in the PHKG2 form.

Genes analysed

Also known as

glycogen storage disease 9; glycogen storage disease type 9; glycogenosis due to phosphorylase kinase deficiency; glycogenosis type 9; glycogenosis type IX; GSD IX; GSD type 9; GSD type IX; GSD9; GSDIX; phosphorylase kinase deficiency

Includes 4 related subtypes ↓
  • glycogen storage disease IXa1
  • glycogen storage disease IXa2
  • glycogen storage disease IXb
  • glycogen storage disease IXc
MONDO:0700291Orphanet 370MedGen 468559

Glycogen Storage Disease Type 0 (Liver Glycogen Synthase Deficiency)

Autosomal recessive

Caused by variants in GYS2, which cause low blood sugar and ketones after overnight fasting in childhood.

What a diagnosis changes

Knowing allows frequent protein-rich meals and bedtime starch to prevent low blood sugar.

Genes analysed

Also known as

glycogen storage disease 0, liver; glycogen storage disease due to glycogen synthase deficiency of liver; glycogen storage disease due to hepatic glycogen synthase deficiency; glycogen storage disease due to liver glycogen synthase deficiency; glycogen storage disease type 0, liver; glycogen storage disease type 0a; glycogen synthase deficiency; glycogenosis type 0a; GSD due to hepatic glycogen synthase deficiency; GSD type 0a; GSD0A; hepatic glycogen synthase deficiency; hypoglycemia with deficiency of glycogen synthetase in the liver; liver GSD 0

MONDO:0009414OMIM 240600Orphanet 2089MedGen 343430

Muscle Glycogen Synthase Deficiency

Autosomal recessive

Caused by variants in GYS1, which causes exercise intolerance and heart muscle disease with a risk of sudden cardiac arrest.

What a diagnosis changes

Knowing allows heart monitoring and advice on safe levels of exercise.

Genes analysed

Also known as

glycogen storage disease 0, muscle; glycogen storage disease due to glycogen synthase deficiency of heart; glycogen storage disease type 0, muscle; glycogen storage disease type 0b; glycogenosis due to muscle and heart glycogen synthase deficiency; glycogenosis type 0b; GSD due to muscle and heart glycogen synthase deficiency; GSD type 0b; GSD0B; heart glycogen storage disease due to glycogen synthase deficiency

MONDO:0012693OMIM 611556Orphanet 137625MedGen 409741

Fanconi-Bickel Syndrome

Autosomal recessive

Caused by variants in SLC2A2 (GLUT2), which cause liver glycogen storage, kidney tubule dysfunction, low blood sugar when fasting and poor growth.

What a diagnosis changes

Knowing allows frequent feeds, slow-release starch and replacement of minerals lost through the kidneys.

Genes analysed

Also known as

Bickel-Fanconi glycogenosis; Fanconi syndrome with intestinal malabsorption and galactose intolerance; Fanconi-Bickel disease; FBS; GLUT2 deficiency; glycogen storage disease 11; glycogen storage disease type 11; glycogen storage disease type XI; glycogen storage disease XI; glycogenosis due to GLUT2 deficiency; glycogenosis Fanconi EXACT; GSD due to GLUT2 deficiency; GSD type 11; GSD type XI; hepatic glycogenosis with amino aciduria and glucosuria; hepatorenal glycogenosis with renal Fanconi syndrome; pseudo-phlorizin diabetes

MONDO:0009216OMIM 227810Orphanet 2088MedGen 501176

Phosphoglycerate Kinase 1 Deficiency

X-linked recessive

Caused by variants in PGK1, which can cause exercise-related muscle cramps and muscle breakdown, haemolytic anaemia or neurological problems.

What a diagnosis changes

Knowing helps avoid strenuous exercise triggers and guides monitoring.

Genes analysed

Also known as

glycogen storage disease caused by mutation in PGK1; glycogenosis due to phosphoglycerate kinase 1 deficiency; GSD due to phosphoglycerate kinase 1 deficiency; PGK deficiency; PGK1 glycogen storage disease; phosphoglycerate kinase 1 deficiency, X-linked recessive; Phosphoglycerate Kinase Deficiency

MONDO:0010392OMIM 300653Orphanet 713MedGen 410166

Phosphoglycerate Mutase Deficiency

Autosomal recessive

Caused by variants in PGAM2, which cause exercise intolerance, muscle cramps and episodes of muscle breakdown.

What a diagnosis changes

Knowing helps avoid triggers of muscle breakdown and supports fast treatment to protect the kidneys.

Genes analysed

Also known as

glycogen storage disease caused by mutation in PGAM2; glycogen storage disease type 10; glycogen storage disease X; glycogenosis due to phosphoglycerate mutase deficiency; GSD due to phosphoglycerate mutase deficiency; GSD type 10; GSD10; GSDX; muscle phosphoglycerate mutase deficiency; myopathy due to phosphoglycerate mutase deficiency; PGAM deficiency; PGAM2 glycogen storage disease

MONDO:0009865OMIM 261670Orphanet 97234MedGen 120613

Muscle Beta-Enolase Deficiency

Autosomal recessive

Caused by variants in ENO3, which cause exercise intolerance, muscle pain and episodes of muscle breakdown.

What a diagnosis changes

Knowing helps avoid triggers of muscle breakdown.

Genes analysed

Also known as

glycogen storage disease 13; glycogen storage disease type 13; glycogen storage disease XIII; glycogenosis due to muscle beta-enolase deficiency; glycogenosis type 13; GSD due to muscle beta-enolase deficiency; GSD13; GSDXIII; muscle enolase deficiency; muscular enolase deficiency

MONDO:0013046OMIM 612932Orphanet 99849MedGen 442873

Lactate Dehydrogenase A Deficiency

Autosomal recessive

Caused by variants in LDHA, which cause exercise-related muscle breakdown and sometimes skin rashes.

What a diagnosis changes

Knowing helps avoid triggers of muscle breakdown and supports fast treatment.

Genes analysed

Also known as

glycogen storage disease caused by mutation in LDHA; glycogen storage disease type 11; glycogen storage disease XI; glycogenosis due to lactate dehydrogenase M-subunit deficiency; glycogenosis type 11; GSD 11; GSD due to lactate dehydrogenase M-subunit deficiency; GSD type 11; GSD XI; GSD11; lactate dehydrogenase deficiency type A; LDH-M subunit deficiency; LDHA glycogen storage disease

MONDO:0013047OMIM 612933Orphanet 284426MedGen 419152

Why whole genome sequencing

Type Ia vs. type Ib distinction determines whether neutropenia management and empagliflozin therapy are needed. This is a genotype-specific treatment decision that standard metabolic workup does not resolve.

Empagliflozin for type Ib neutropenia is a breakthrough, but is only indicated with confirmed SLC37A4 genotype

GSD type Ib patients accumulate 1,5-anhydroglucitol-6-phosphate (1,5-AG6P) in neutrophils, causing neutrophil dysfunction and neutropenia. Empagliflozin, by blocking renal glucose reabsorption, lowers circulating 1,5-AG levels and reduces neutrophil 1,5-AG6P accumulation, restoring neutrophil counts and function. Multiple case series demonstrate dramatic improvements in neutropenia, mucosal ulceration, and inflammatory bowel disease symptoms. This therapy is specific to the SLC37A4 translocase defect; G6PC-deficient (type Ia) patients do not accumulate 1,5-AG6P and do not benefit. Molecular genotyping identifies the appropriate candidates.

Hepatic adenomas develop in 50-75% of GSD-I patients: surveillance for malignant transformation requires lifelong imaging

Hepatocellular adenomas (HCA) are a major long-term complication of GSD-I, developing in the majority of patients by adulthood. While most HCA remain benign, malignant transformation to hepatocellular carcinoma (HCC) occurs, requiring regular hepatic imaging (ultrasound, MRI) and alpha-fetoprotein monitoring. Confirmed molecular GSD-I diagnosis ensures that the patient is enrolled in the appropriate hepatic surveillance protocol. Additionally, molecular diagnosis enables carrier testing for siblings and reproductive planning for affected adults.

Other metabolic conditions

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