CPT® Code 81271

The CPT® Code 81271 pertains to the molecular genetic testing of the HTT (huntingtin) gene, specifically aimed at evaluating and detecting abnormal alleles associated with Huntington disease. Huntington disease is a progressive neurodegenerative disorder characterized by a range of symptoms including cognitive impairment, dementia, apathy, depression, anxiety, and extrapyramidal body movements. The HTT gene, located on the short (p) arm of chromosome 4 at position 16.3 (4p16.3), encodes a protein that plays a crucial role in the function of nerve cells, which is essential for normal brain development. This gene is involved in various cellular processes, including chemical signaling, protein binding, and cellular protection against self-destruction. The HTT gene features a unique DNA allele characterized by a trinucleotide repeat pattern of three amino acids: cysteine, alanine, and glycine (CAG). Typically, this CAG sequence repeats between 10 to 35 times in healthy individuals. However, when the number of repeats exceeds this range, it can lead to the production of an elongated protein that is fragile and prone to fragmentation, resulting in the accumulation of toxic aggregates within nerve cells. The presence of 27 to 35 CAG repeats is classified as a pre-mutation, where individuals remain asymptomatic but face an increased risk of allele expansion in subsequent generations. Alleles with 36 to 39 CAG repeats may present with mild or no symptoms, while those with 40 to 50 CAG repeats typically manifest symptoms in adulthood. In contrast, individuals with more than 60 CAG repeats often exhibit symptoms during childhood or adolescence. The analysis performed under CPT® Code 81271 is crucial for identifying these expanded alleles, thereby aiding in the diagnosis and understanding of Huntington disease.