Glycogen Storage Disorders Panel, Sequencing

Last Literature Review: August 2021 Last Update:

Preferred molecular test to confirm or rule out a diagnosis of a GSD or related disorder following clinical and/or biochemical presentation

Glycogen storage diseases (GSDs) are a group of inborn errors of metabolism, typically caused by enzyme defects, resulting in a buildup of glycogen in the liver, muscles, and other organs. Specific clinical presentation and age of onset depends on the particular type of GSD; there are many types and subtypes, and other disorders may have overlapping phenotypes.

Disease Overview

Common clinical features of these disorders include:

  • Hepatomegaly
  • Poor growth or short stature
  • Hypoglycemia (marked by fatigue, irritability, headaches, pallor)
  • Muscle weakness and/or pain
  • Cardiomyopathy
  • Exercise intolerance
  • Liver disease (cirrhosis)

Testing Strategy

Depending on the type of GSD suspected, consideration may be given to laboratory workup that may include the following tests:

  • Serum creatine kinase
  • Blood glucose (fasting/nonfasting)
  • Cholesterol
  • Liver enzymes (eg, alanine transaminase [ALT] and aspartate transaminase [AST])
  • Triglycerides
  • Uric acid
  • Urine organic acids
  • Plasma acylcarnitines
  • Blood lactate
  • Imaging studies (magnetic resonance imaging [MRI] or ultrasound)
  • Tissue biopsy

Genetics

Etiology

Pathogenic germline variants in genes associated with GSDs or related disorders (see Genes Tested table)

Inheritance

Primarily autosomal recessive (AR); rarely autosomal dominant (AD) or X-linked (XL)

Penetrance

Variable, depending on the specific type of GSD

Test Interpretation

Clinical Sensitivity

Variable, depending on the specific type of GSD

Analytic Sensitivity:

For massively parallel sequencing:

Variant Class Analytic Sensitivity (PPA) Estimatea (%) Analytic Sensitivity (PPA) 95% Credibility Regiona (%)

SNVs

99.2

96.9-99.4

Deletions 1-10 bp

93.8

84.3-98.2

Deletions 11-44 bp

99.9

87.8-100

Insertions 1-10 bp

94.8

86.8-98.5

Insertions 11-23 bp

99.9

62.1-100

aGenes included on this test are a subset of a larger methods-based validation from which the PPA values are derived.

bp, base pairs; PPA, positive percent agreement; SNVs, single nucleotide variants

Results

Result Variant(s) Detected Clinical Significance

Positive

One or more pathogenic or likely pathogenic variants detected

Confirms a diagnosis of heritable GSD or related disorder

Specific diagnosis depends on the variant(s) detected

See note

One or more variants of uncertain significance detected

Unknown if variant(s) are disease-causing or benign

Negative

No pathogenic variants detected

Diagnosis of GSD or related disorder is less likely, though not excluded

Limitations

  • A negative result does not exclude a diagnosis of a GSD.
  • Diagnostic errors can occur due to rare sequence variations.
  • Interpretation of this test result may be impacted if this patient has had an allogeneic stem cell transplantation.
  • The following will not be evaluated:
    • Variants outside the coding regions and intron-exon boundaries of targeted gene(s)
    • Regulatory region and deep intronic variants, including GBE1 (NM_000158.4) intron 15
      • Includes an Ashkenazi Jewish founder mutation in GBE1 (HGMD ID: CX153579)
    • Noncoding transcripts
    • The following exons are not sequenced due to technical limitations of the assay:
      • ENO3 (NM_001374524) exon(s) 1
      • OXCT1 (NM_001364299) exon(s) 5
      • OXCT1 (NM_001364300) exon(s) 1
      • OXCT1 (NM_001364303) exon(s) 1
      • PFKM (NM_001354735) exon(s) 4
      • PFKM (NM_001354736) exon(s) 4
      • PFKM (NM_001354740) exon(s) 1
      • PFKM (NM_001354741) exon(s) 2
    • Large deletions/duplications in any of the tested genes
  • The following may not be detected:
    • Deletions/duplications/insertions of any size by massively parallel sequencing
    • Some variants due to technical limitations in the presence of pseudogenes, repetitive, or homologous regions
    • Low-level somatic variants

Genes Tested

Gene MIM # Disorder Inheritance

ACAT1

607809

Alpha-methylacetoacetic aciduria

AR

AGL

610860

GSD IIIa

AR

GSD IIIb

AR

ALDOA

103850

GSD XII

AR

ALDOB

612724

Hereditary fructose intolerance

AR

CPT2

600650

Carnitine palmitoyltransferase II deficiency

AD, AR

ENO3

131370

GSD XIII

AR

FBP1

611570

Fructose-1, 6-bisphosphatase deficiency

AR

G6PC

613742

GSD Ia

AR

GAA

606800

GSD II (Pompe disease)

AR

GBE1

607839

GSD IV

AR

GYG1

603942

GSD XV

AR

GYS1

138570

GSD 0, muscle

AR

GYS2

138571

GSD 0, liver

AR

LAMP2

309060

Danon disease

XL

LDHA

150000

GSD XI

AR

NHLRC1

608072

Myoclonic epilepsy of Lafora

AR

OXCT1

601424

Succinyl-CoA:3-oxoacid CoA transferase deficiency

AR

PFKM

610681

GSD VII

AR

PGAM2

612931

GSD X

AR

PGK1

311800

Phosphoglycerate kinase 1 deficiency

XL

PGM1

171900

Congenital disorder of glycosylation type It

AR

PHKA1

311870

GSD IXd

XL

PHKA2

300798

GSD IXa1

XL

GSD IXa2

XL

PHKB

172490

GSD IXb

AR

PHKG2

172471

GSD IXc

AR

PRKAG2

602743

Hypertrophic cardiomyopathy 6

AD

GSD of heart

AD

Wolff-Parkinson-White syndrome

AD

PYGL

613741

GSD VI

AR

PYGM

608455

GSD V (McArdle disease)

AR

RBCK1

610924

Polyglucosan body myopathy 1

AR

SLC16A1

600682

Erythrocyte lactate transporter defect;

AD

Familial hyperinsulinemic hypoglycemia 7

AD

Monocarboxylate transporter 1 deficiency

AD, AR

SLC2A2

138160

Fanconi Bickel syndrome

AR

SLC37A4

602671

GSD Ib

AR

GSD Ic

AR

Additional Resources