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Related Experiment Videos

Molecular basis for glucose-galactose malabsorption.

Ernest M Wright1, Eric Turk, Martin G Martin

  • 1Department of Physiology, UCLA School of Medicine, Los Angeles, CA 90095-1751, USA. ewright@mednet.ucla.edu

Cell Biochemistry and Biophysics
|July 26, 2002
PubMed
Summary

Mutations in the sodium-glucose cotransporter 1 (SGLT1) gene cause glucose-galactose malabsorption (GGM) in infants. These genetic defects impair sugar transport by producing nonfunctional or improperly targeted SGLT1 proteins.

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Area of Science:

  • Genetics
  • Molecular Biology
  • Gastroenterology

Background:

  • Glucose-galactose malabsorption (GGM) is a severe, life-threatening inherited disorder in newborns.
  • GGM symptoms include severe diarrhea triggered by dietary sugars like lactose, glucose, and galactose.

Purpose of the Study:

  • To investigate if mutations in the sodium-glucose cotransporter 1 (SGLT1) gene are the cause of GGM.
  • To identify and characterize mutations in the SGLT1 gene in GGM patients.

Main Methods:

  • Isolated human SGLT1 cDNA (hSGLT1) and mapped the gene to chromosome 22q13.1.
  • Screened 46 GGM patients for SGLT1 mutations, identifying various types including missense, nonsense, and frameshift.
  • Utilized the Xenopus laevis oocyte expression system to assess the functional impact of identified mutations on sugar transport.

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Main Results:

  • Identified causative mutations in the SGLT1 gene in all 46 GGM patients studied.
  • Nonsense, frameshift, and splice site mutations resulted in truncated, nonfunctional SGLT1 proteins.
  • Most missense mutations led to stable but mis-trafficked SGLT1 proteins that did not reach the plasma membrane; one mutant showed impaired sugar transport despite membrane localization.

Conclusions:

  • Mutations in the SGLT1 gene are definitively the cause of glucose-galactose malabsorption.
  • Impaired sugar transport in GGM is primarily due to truncated SGLT1 proteins or defects in their trafficking to the cell membrane.