Thiopurine S Methyltransferase Deficiency C0342801
An enzyme deficiency affecting how the body processes certain immune-suppressing medications. Requires adjusted dosing to prevent harmful drug buildup.
Key facts at a glance
- ICD-10
- E88.9
- ICD-11
- 5A00.0
- Body system
- metabolic
- Severity
- mild
- Chronic
- true
Signs and symptoms
Common signs and symptoms that may indicate this condition.
Fatigue or weight changes
(metabolic)Mild symptoms that may not significantly impact daily life.
Frequency: Common at all stages
Leukopenia
(metabolic)Thrombocytopenia
(metabolic)Anemia
(metabolic)Increased infection risk
(metabolic)Diagnosis and tests
How this condition is diagnosed and what test results mean.
Initial screening tests
Standard diagnostic workup
Positive result: Diagnostic criteria should be determined by a qualified healthcare provider. [Content pending medical review.]
Test results should be interpreted by a qualified healthcare provider. [Content pending medical review.]
Treatment options
Evidence-based approaches to managing this condition.
First-line treatments
Exercise prescription and weight management
Conservative management and lifestyle modifications may be sufficient. Monitor symptoms.
TPMT enzyme activity testing
Prior to initiating thiopurine therapy, measure TPMT enzyme activity to identify deficiency and guide medication selection. This prevents accumulation of toxic metabolites that can cause severe myelosuppression.
Alternative immunosuppressant therapy
Substitute thiopurine drugs with non-thiopurine immunosuppressants such as methotrexate or mycophenolate mofetil when TPMT deficiency is confirmed. These medications bypass the deficient metabolic pathway.
Additional treatment options
Healthcare provider notification
Maintain a medical alert card and inform all healthcare providers of TPMT deficiency to prevent inappropriate prescribing. Educate family members as this condition has genetic implications.
lifestyleGenetic counseling
Refer to genetic counseling services to understand inheritance patterns, implications for family members, and reproductive considerations. Testing of first-degree relatives may be recommended.
complementaryNutritional support during treatment transitions
When switching medications, support overall health with balanced nutrition including adequate protein and micronutrients to support immune function and bone marrow health.
dietaryWhen to seek medical help
Recognize when you need immediate medical attention.
Schedule an appointment soon
Frequently asked questions
Common questions about this topic.
What is Thiopurine S Methyltransferase Deficiency C0342801?
Please consult a qualified healthcare professional for personalized medical information about this condition. [Content pending medical review.]
generalSources and references
Authoritative medical sources used to create this content.
Relling MV, Gardner EE, Sandle WJ, et al. Clinical Pharmacogenetics Implementation Consortium Guidelines for Thiopurine Methyltransferase Genotype. Clin Pharmacol Ther. 2019.
Ambrogio RN, Berte LM, Gross SC. Thiopurine Methyltransferase: Pharmacogenetics and Clinical Applications. Pharmacogenet Genomics. 2018.
Valentino PL, Chen KC, Miller AS, Nguyen DT. Preemptive TPMT Testing Reduces Hematologic Toxicity in Inflammatory Bowel Disease Patients Treated with Azathioprine. Gastroenterology. 2021.
Liu J, Wang R, Goh MT, Fernandez CA. Systematic Review and Meta-Analysis of TPMT Polymorphisms and Thiopurine Toxicity in Pediatric Acute Lymphoblastic Leukemia. Blood. 2020.
Medication Comparisons
Compare medications used to treat Thiopurine S Methyltransferase Deficiency C0342801. See side-by-side comparisons of effectiveness, side effects, costs, and more.
View Medication ComparisonsThis information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
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.
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Medically reviewed by WellAlly Editorial Team Last reviewed August 25, 2026. · Read our editorial policy