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Genetic test for CAG repeat expansion in the TBP gene (TATA-binding protein)

Published: August 9, 2026Updated: August 16, 2026

This test measures the number of repeated CAG sequences in the TATA-binding protein (TBP) gene, which may be linked to certain genetic conditions.

Quick summary

["This test helps assess genetic risk for conditions associated with abnormal CAG repeat expansions."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
33981-2
Short code
TBP gene CAG Rpt Bld/T Ql
Synonyms
TBP gene CAG Rpt Bld/T Ql
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Ref low
0.8
Ref high
1.2
Critical range
— – 5 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
molgen
CPT
85610
SNOMED
396252006
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

Why This Test Might Be Ordered

Your healthcare provider may recommend this test if you have a family history of conditions like spinocerebellar ataxia (SCA) or other neurodegenerative disorders linked to TBP gene mutations. It can also be part of genetic counseling for individuals with suspected inherited genetic conditions.

What to Expect Before the Test

No special preparation is needed. A blood sample will be taken from a vein in your arm. You may feel a slight pinch, but it usually doesn’t cause discomfort. If you have a blood disorder or are on blood thinners, let your provider know before the test.

What the Test Results Mean

Results are typically reported as the number of CAG repeats in your TBP gene. Normal ranges vary, and abnormal expansions (often 30 or more repeats) may indicate an increased risk for genetic conditions. Your healthcare provider will discuss the results with you in detail.

Common Conditions Linked to TBP Gene Variations

Abnormal CAG repeat expansions in the TBP gene are associated with spinocerebellar ataxia (SCA) types, which affect movement and coordination. Other rare conditions may also be linked, so results are interpreted based on your medical history and family background.

Reference range

INR: 0.8-1.2 (warfarin: 2.0-3.0)N/A

Specimen: whole-blood

Inform your healthcare provider if you are taking blood thinners. No special preparation required.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

TBP Gene CAG Repeat Test

Frequently asked questions

What does a normal result mean for me?
A normal result means your CAG repeat count in the TBP gene is within the typical range for healthy individuals. However, genetic testing is often part of a broader evaluation, so your provider will consider other factors, including family history.
Can this test detect all genetic conditions?
No, this test specifically measures CAG repeats in the TBP gene. It won’t detect mutations in other genes. If your provider suspects a different genetic condition, additional tests may be recommended.
How often should I get this test?
This test is usually done once, often as part of genetic testing for a specific condition or family history. If you have a family member with a known TBP-related disorder, your provider may recommend monitoring or repeat testing in the future.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy