CPT® Code 81335

The CPT® Code 81335 pertains to the gene analysis of the thiopurine S-methyltransferase (TPMT) gene, specifically focusing on common variants such as *2 and *3. The TPMT gene is crucial as it encodes the enzyme thiopurine S-methyltransferase, which is responsible for the S-methylation process of certain compounds that metabolize thiopurine drugs. These drugs are often utilized in medical treatments that require immune suppression, including conditions like acute lymphoblastic leukemia (ALL), inflammatory bowel disease, various rheumatic disorders, and in the context of organ transplantation. The TPMT gene is situated on the short arm of chromosome 6 at position 22.3, and its analysis is vital for identifying genetic variants that may influence an individual's response to thiopurine medications. The significance of this gene analysis lies in its ability to predict the risk of severe adverse effects associated with thiopurine therapy, particularly bone marrow toxicity and myelosuppression. There are four primary variant alleles that account for over 95% of cases with reduced TPMT enzyme activity: TPMT*2 (238G>C), TPMT*3A (460G>A or 719A>G), TPMT*3B (460G>A), and TPMT*3C (719A>G). Individuals with two normal alleles (TPMT*1) are generally at a low risk for drug toxicity, while those with one variant allele may experience decreased enzyme activity, necessitating a potential reduction in drug dosage. Conversely, individuals possessing two variant alleles face a significantly heightened risk for severe side effects due to minimal or absent enzyme activity. The analysis is performed on samples obtained from blood or buccal cells, which are processed using polymerase chain reaction (PCR) amplification techniques combined with single nucleotide primer extension (SNPE) and fluorescence observation to accurately identify these genetic variants.