CPT® Code 81121

The CPT® Code 81121 pertains to the analysis of the IDH2 gene, specifically focusing on common variants such as R140W and R172M, which are associated with glioma tumors. Gene analysis is a critical procedure that helps in identifying mutations in the isocitrate dehydrogenase 1 (IDH1) and 2 (IDH2) genes, both of which play significant roles in the development of gliomas, the most prevalent type of primary brain tumors. Gliomas originate from glial cells, which are supportive cells in the brain and spinal cord, and can be classified into various types, including astrocytomas, ependymomas, and oligodendrogliomas. The IDH1 gene is located on the long (q) arm of chromosome 2 at position 34, while the IDH2 gene is found on the long (q) arm of chromosome 15 at position 26.1. The IDH1 gene encodes the enzyme isocitrate dehydrogenase 1, which is primarily located in the cytoplasm and peroxisomes, whereas the IDH2 gene encodes isocitrate dehydrogenase 2, which is situated in the mitochondria. These enzymes are responsible for converting isocitrate to 2-ketoglutarate, a process that also generates NADPH, a molecule that protects cells from oxidative stress. Mutations in the IDH1 and IDH2 genes disrupt the normal function of these enzymes, leading to the abnormal production of D-2-hydroxyglutarate. This compound interferes with cell maturation and promotes the overproduction of immature cells, contributing to the formation of glioma tumors. The procedure for testing involves obtaining tumor tissue samples, which are then processed through DNA extraction and amplification using polymerase chain reaction (PCR) techniques. Specific primers targeting IDH1 codon 132 and IDH2 codon 172 are utilized, followed by pyrosequencing to analyze the presence or absence of these gene mutations. This analysis is essential for stratifying the prognosis of glioma tumors and guiding treatment decisions.