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PubMed This is a summary of 16 peer-reviewed journal articles Updated
Gastroenterology

How CSID is Diagnosed

At a Glance

Congenital Sucrase-Isomaltase Deficiency (CSID) is diagnosed through an upper endoscopy (EGD) with a biopsy to measure enzyme levels in the small intestine. Non-invasive genetic testing for SI gene mutations and sucrose breath tests are also used to confirm the condition.

To confirm a diagnosis of Congenital Sucrase-Isomaltase Deficiency (CSID), doctors must look beyond surface symptoms to the biological root: the SI gene and the enzymes it creates. This gene provides the instructions for making the sucrase-isomaltase (SI) enzyme complex [1]. These enzymes sit on the finger-like projections of your small intestine (villi) and act as “chemical scissors” to break down complex sugars and starches into simple fuels the body can use [2].

The Genetics of CSID

For many years, CSID was considered a strictly “autosomal recessive” condition, meaning a person needed two faulty copies of the SI gene to show symptoms [3][4]. We now understand that the genetics are more complex:

  • Biallelic (Homozygous or Compound Heterozygous): Inheriting two mutated genes usually leads to the “classical” presentation—a near-total lack of enzyme activity and severe symptoms starting in infancy [5][6].
  • Heterozygous: Inheriting only one mutated gene. While once thought to be “silent carriers,” many of these individuals actually have reduced enzyme levels and suffer from chronic gas, bloating, and diarrhea that may be misdiagnosed as IBS [7][8][9].

Common mutations identified in research include p.Val577Gly, p.Gly1073Asp, and the Arctic-specific c.273_274delAG variant [1][10].

Diagnostic Tools

There are three primary ways doctors confirm CSID. Each has its own strengths and is often used in combination.

1. The Gold Standard: EGD with Disaccharidase Assay

This involves an esophagogastroduodenoscopy (EGD), where a doctor takes small tissue samples (biopsies) from the small intestine while the patient is under sedation [11][7].

  • What they look for: The lab measures the actual activity level of enzymes like sucrase, lactase, maltase, and palatinase [7][12].
  • The hallmark of CSID: In CSID, the intestinal structure (villi) usually looks perfectly healthy, but the sucrase activity is significantly low or absent [13][14].

2. Non-Invasive: Genetic Testing

A simple blood draw or saliva swab can identify mutations in the SI gene [5]. This is increasingly used as a first step because it avoids the risks of sedation and endoscopy [14][4].

3. Breath Testing (13C-SBT)

The 13C-sucrose breath test requires the patient to drink a sucrose solution. As the body attempts to break down the sugar, it releases labeled carbon dioxide that can be measured in the breath [15]. If the levels are low, it indicates the body isn’t successfully digesting the sucrose [15][16].

Checklist for Your Medical Records

When reviewing your results, ensure the following information is present to help confirm an accurate diagnosis:

  • [ ] Enzyme Activity Levels: Are the numerical values for sucrase and palatinase (the standard lab marker used to measure isomaltase) clearly listed? [14]
  • [ ] Reference Ranges: Does the report include the “normal” range for the lab so you can see how low your levels are? [12]
  • [ ] Pathology Description: Does the report confirm that the intestinal villi appear “normal” or “unremarkable”? (This helps rule out Celiac disease). [13]
  • [ ] Genetic Mutation Name: If you had genetic testing, is the specific mutation (e.g., p.Val577Gly) identified? [1]
  • [ ] Zygosity: Does the genetic report state if you are homozygous (two copies) or heterozygous (one copy)? [4]

Next steps: Treatment and Dietary Management

Common questions in this guide

What is the gold standard test for diagnosing CSID?
The gold standard for diagnosing CSID is an esophagogastroduodenoscopy (EGD) with a disaccharidase assay. During this procedure, a doctor takes small tissue biopsies from the small intestine to directly measure the activity levels of digestive enzymes like sucrase and maltase.
Can genetic testing alone diagnose CSID?
Yes, genetic testing using a simple blood draw or saliva swab can identify mutations in the SI gene that cause CSID. This non-invasive test is increasingly used as a first diagnostic step because it avoids the risks associated with sedation and endoscopy.
How does a breath test work for CSID?
During a 13C-sucrose breath test, you drink a specific sucrose solution. Your body's ability to digest the sugar is then measured by analyzing the carbon dioxide released in your breath. Low levels of carbon dioxide indicate that your body is not properly breaking down the sucrose.
If my intestinal biopsy looked normal, could I still have CSID?
Yes, in people with CSID, the physical structure of the intestines and villi typically look perfectly healthy under a microscope. A diagnosis relies on measuring the actual enzyme activity from the tissue sample or identifying a genetic mutation, rather than looking at tissue damage.
Does having only one mutated SI gene cause symptoms?
Yes, inheriting just one mutated SI gene can lead to reduced enzyme levels and noticeable symptoms. Many people with a single genetic variant experience chronic gas, bloating, and diarrhea that is sometimes misdiagnosed as Irritable Bowel Syndrome (IBS).

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Can you explain the specific numerical values of sucrase and isomaltase activity from my biopsy report and how they compare to the laboratory's reference range?
  2. 2.Do my genetic test results show a homozygous mutation or a heterozygous variant, and how does that influence the severity of my symptoms?
  3. 3.If my biopsy showed normal intestinal anatomy (villi), how does that help rule out other conditions like Celiac disease while supporting a CSID diagnosis?
  4. 4.Since reference values for enzyme activity can vary, does this clinic use pediatric or adult standards for interpreting my results?
  5. 5.If we choose a non-invasive breath test, how does its accuracy compare to the 'gold standard' biopsy in my specific case?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (16)
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    Functional variants in the sucrase-isomaltase gene associate with increased risk of irritable bowel syndrome.

    Henström M, Diekmann L, Bonfiglio F, et al.

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    Sucrase-Isomaltase Deficiency Causing Persistent Bloating and Diarrhea in an Adult Female.

    Chiruvella V, Cheema A, Arshad HMS, et al.

    Cureus 2021; (13(4)):e14349 doi:10.7759/cureus.14349.

    PMID: 33972906
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    Congenital sucrase-isomaltase deficiency in Türkiye; a single center experience.

    Barut D, Kıran Taşcı E, Kunay B, et al.

    Scandinavian journal of gastroenterology 2024; (59(6)):647-651 doi:10.1080/00365521.2024.2324961.

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    Congenital Sucrase-Isomaltase Deficiency: Same Mutation with Different Clinical Presentations.

    İryancı Fİ, Güven B, Çakır M

    The Turkish journal of gastroenterology : the official journal of Turkish Society of Gastroenterology 2024; (35(4)):343-349 doi:10.5152/tjg.2024.23250.

    PMID: 39128102
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    Two Novel Mutations in the SI Gene Associated With Congenital Sucrase-Isomaltase Deficiency: A Case Report in China.

    Zhou J, Zhao Y, Qian X, et al.

    Frontiers in pediatrics 2021; (9()):731716 doi:10.3389/fped.2021.731716.

    PMID: 34926337
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    Molecular pathogenicity of novel sucrase-isomaltase mutations found in congenital sucrase-isomaltase deficiency patients.

    Gericke B, Amiri M, Scott CR, Naim HY

    Biochimica et biophysica acta. Molecular basis of disease 2017; (1863(3)):817-826 doi:10.1016/j.bbadis.2016.12.017.

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    Sucrase-isomaltase Gene Variants in Patients With Abnormal Sucrase Activity and Functional Gastrointestinal Disorders.

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    Heterozygotes Are a Potential New Entity among Homozygotes and Compound Heterozygotes in Congenital Sucrase-Isomaltase Deficiency.

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    Exploring congenital sucrase-isomaltase deficiency in autism spectrum disorder patients with irritable bowel syndrome symptoms: A prospective SI gene sequencing study.

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    Genetic Loss of Sucrase-Isomaltase Function: Mechanisms, Implications, and Future Perspectives.

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    Clinical Characteristics of Disaccharidase Deficiencies Among Children Undergoing Upper Endoscopy.

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    Congenital sucrase-isomaltase deficiency: diagnostic challenges and response to enzyme replacement therapy.

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    13C-Labeled-Starch Breath Test in Congenital Sucrase-isomaltase Deficiency.

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    The Role of Disaccharidase Deficiencies in Functional Abdominal Pain Disorders-A Narrative Review.

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This page explains diagnostic testing for Congenital Sucrase-Isomaltase Deficiency (CSID) for educational purposes. Always consult a gastroenterologist or medical geneticist to interpret your specific biopsy, breath test, or genetic screening results.

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