Disorders of galactose metabolism (WP5173)

Homo sapiens

Galactose is converted into glucose 1-phosphate (G1P) through a series of steps called the Leloir pathway. The first step of the pathway is the phosphorylation of galactose by galactokinase (encoded GALK1) to yield galactose 1-phosphate. Conversion of galactose 1-phosphate to G1P requires the transfer of UDP from UDP-glucose catalyzed by GALT. UDP-galactose is converted to UDP-glucose by GALE. Glucose-1-phosphate is converted to glucose-6-phosphate by phosphoglucomutase (PGM) and vice versa. There are two known disorders concerning the uptake transports of galactose (SGLT1 and GLUT2 deficiency) and three known disorders of galactose metabolism: galactokinase deficiency (GALK-D), galactose 1-phosphate uridyltransferase deficiency (galactosemia, GALT-D) and uridine diphosphate galactose 4-epimerase deficiency (GALE-D). Among these, galactosemia is the most common and most severe. This pathway was inspired by Chapter 18, figure 18.3 of the book of Blau (4th edition; ISBN: 978-3-642-40337-8).


Alexandra Bosch , Enzo Chiaradia , Egon Willighagen , Denise Slenter , Lars Willighagen , and Eric Weitz


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Homo sapiens


Inherited Metabolic Disorders (IMD) Pathways Rare Diseases


Pathway Ontology

GALE deficiency pathway disease pathway glycolysis pathway classic metabolic pathway altered galactose metabolic pathway galactose metabolic pathway carbohydrate metabolic pathway

Disease Ontology

glycogen storage disease VI galactosemia glycogen storage disease XV glycogen storage disease IV galactose epimerase deficiency congenital disorder of glycosylation It galactokinase deficiency glycogen storage disease


Label Type Compact URI Comment
Glycogen (n+1) Metabolite cas:9005-79-2
Glycogen Metabolite chebi:28087
Glucose-1-phosphate Metabolite chebi:16077
Galactitol Metabolite hmdb:HMDB0000107
UDP-galactose Metabolite chebi:67119
UDP-glucose Metabolite chebi:18066
Galactose Metabolite chebi:28260
Galactose-1-phosphate Metabolite chebi:17973
Glucose-6-phosphate Metabolite hmdb:HMDB0001401 search for glucose 6-phosphate
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D-galactonate Metabolite chebi:12931
Galactose Metabolite chebi:28260
Galactose Metabolite chebi:28260
GYS1 GeneProduct ensembl:ENSG00000104812 catalyzes the rate-limiting step in glycogen synthesis in the liver and in skeletal muscle: the transfer of glucose monomers from UDP-glucose to the terminal branch of the growing glycogen chain via the formation of α(1→4) glycosidic bonds
GYS1: specific to skeletal muscle
GBE1 GeneProduct ensembl:ENSG00000114480 glycogen branching enzyme that catalyzes the transfer of alpha-1,4-linked glucosyl units from the outer end of a glycogen chain to an alpha-1,6 position on the same or a neighboring glycogen chain
PYGL GeneProduct ensembl:ENSG00000100504
GYG2 GeneProduct ensembl:ENSG00000056998 expressed mainly in liver, cardiac muscle and other types of tissue, but not in skeletal muscle.
GYG1 GeneProduct ensembl:ENSG00000163754 Glycogenin-1 is involved in the biosynthesis of glycogen. It is capable of self-glucosylation, forming an oligosaccharide primer that serves as a substrate for glycogen synthase. It also plays a role in glycogen metabolism regulation
expressed mostly in muscles
GYS2 GeneProduct ensembl:ENSG00000111713 GYS2: specific to liver
AKR1B1 GeneProduct ensembl:ENSG00000085662
GALE GeneProduct ensembl:ENSG00000117308
PGM1 GeneProduct ensembl:ENSG00000079739
GALT GeneProduct ensembl:ENSG00000213930
SLC5A1 GeneProduct ensembl:ENSG00000100170
GALK1 GeneProduct ensembl:ENSG00000108479
SLC2A2 GeneProduct ensembl:ENSG00000163581
galactose dehydrogenase Protein eccode: 'This enzyme is part of the De Ley-Doudoroff pathway, which is used by some bacteria during growth on D-galactose.' Source: [https://enzyme.expasy.org/EC/]


  1. Physician’s Guide to the Diagnosis, Treatment, and Follow-Up of Inherited Metabolic Diseases [Internet]. Blau N, Duran M, Gibson KM, Dionisi Vici C, editors. Springer Berlin Heidelberg; 2014. Available from: http://dx.doi.org/10.1007/978-3-642-40337-8 DOI Scholia
  2. Hypoglycemia. Koren D, Palladino A. In: Genetic Diagnosis of Endocrine Disorders [Internet]. Elsevier; 2016. p. 31–75. Available from: http://dx.doi.org/10.1016/B978-0-12-800892-8.00003-8 DOI Scholia
  3. Galactose supplementation in phosphoglucomutase-1 deficiency; review and outlook for a novel treatable CDG. Morava E. Mol Genet Metab. 2014 Aug;112(4):275–9. PubMed Europe PMC Scholia
  4. Galactose metabolism and health. Coelho AI, Berry GT, Rubio-Gozalbo ME. Curr Opin Clin Nutr Metab Care. 2015 Jul;18(4):422–7. PubMed Europe PMC Scholia