CPT® Code 81329

SMN1 (survival of motor neuron 1, telomeric) (eg, spinal muscular atrophy) gene analysis; dosage/deletion analysis (eg, carrier testing), includes SMN2 (survival of motor neuron 2, centromeric) analysis, if performed

The CPT® Code 81329 pertains to the molecular genetic testing of the SMN1 (survival of motor neuron 1, telomeric) gene, which is crucial in the context of spinal muscular atrophy (SMA), a serious neuromuscular disorder characterized by the degeneration of motor neurons. This testing includes dosage and deletion analysis, which is essential for carrier testing. The analysis may also encompass the SMN2 (survival of motor neuron 2, centromeric) gene if it is performed. The SMN1 gene is located on the long (q) arm of chromosome 5 at position 13.2 (5q13.2) and is responsible for producing a protein that plays a vital role in the transport of signals through motor neurons to voluntary muscles, which are necessary for functions such as walking, talking, and swallowing. The protein produced by the SMN1 gene is fully functional and accounts for approximately 85-90% of the total SMN protein in the body, while the SMN2 gene contributes the remaining 10-15% through its production of two protein isoforms, only one of which is functional. The presence of multiple copies of the SMN1 and SMN2 genes can influence the risk of transmitting SMA to offspring, with deletions in both copies of the SMN1 gene being present in 95% of cases. The testing provided by code 81329 is instrumental in identifying deletion mutations and counting gene copies, which aids in understanding the genetic landscape of SMA and its inheritance patterns.