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SAR1B gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

SAR1B gene

The SAR1B gene provides instructions for making a protein essential for the transport of chylomicrons, which are necessary for the absorption of dietary fats and fat-soluble vitamins.

Normal Function

The SAR1B gene provides instructions for making a protein that is produced in a variety of tissues, with most research focusing on its role in the digestive tract. The SAR1B protein is required for the transport of molecules called chylomicrons.

During digestion, chylomicrons are formed within cells called enterocytes that line the small intestine. These molecules are essential for absorbing fat-soluble vitamins (vitamins K, E, and D) and carrying fats and cholesterol from the small intestine into the bloodstream. Within enterocytes, SAR1B proteins help transport immature chylomicrons from the endoplasmic reticulum to the Golgi apparatus for processing. Once matured, these chylomicrons are released into the bloodstream to support normal growth and development. In other tissues, such as the heart and muscles, the SAR1B protein is likely involved in transporting calcium within cells.

Health Conditions Related to Genetic Changes

Chylomicron retention disease

More than 20 mutations in the SAR1B gene have been found to cause chylomicron retention disease, an inherited disorder that impairs the absorption of fats, cholesterol, and fat-soluble vitamins. These mutations disrupt the protein's ability to transport chylomicrons, preventing their release into the bloodstream and leading to nutritional and developmental problems.

Other Names for This Gene

  • GTP-binding protein Sara
  • SAR1 gene homolog B (S. cerevisiae)
  • SAR1 homolog B (S. cerevisiae)
  • SAR1a gene homolog 2
  • SAR1B_HUMAN
  • SARA2
  • secretion associated, Ras related GTPase 1B

Frequently Asked Questions

Supplementation can normalize serum vitamin levels and prevent complications such as rickets (vitamin D) or coagulopathy (vitamin K). However, because chylomicron transport remains impaired, patients may still require lifelong high‑dose or water‑soluble formulations and periodic re‑evaluation to ensure adequate tissue stores.
low‑fat, medium‑chain triglyceride (MCT) diet is usually recommended because MCTs are absorbed directly into the portal circulation, bypassing the need for chylomicron formation. Supplementation with fat‑soluble vitamins (A, D, E, K) in water‑soluble or high‑dose forms is essential, and regular monitoring of growth parameters and vitamin levels guides adjustments.
Many insurers cover SAR1B testing when it is ordered to explain a clear clinical picture of fat malabsorption, especially after other causes have been excluded. Prior authorization and a detailed physician’s note describing the suspected chylomicron retention disease improve the likelihood of coverage.
Typical clues include chronic diarrhea or fatty (steatorrhea) stools, failure to thrive despite adequate calories, and low blood levels of fat‑soluble vitamins (especially vitamin D and E). Laboratory tests often reveal low serum triglycerides, low cholesterol, and markedly reduced apolipoprotein B.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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