CPT® Code 81312

PABPN1 (poly[A] binding protein nuclear 1) (eg, oculopharyngeal muscular dystrophy) gene analysis, evaluation to detect abnormal (eg, expanded) alleles

Molecular genetic testing is conducted to identify abnormal, expanded alleles on the PABPN1 (poly[A] binding protein nuclear 1) gene, which is associated with oculopharyngeal muscular dystrophy (OPMD), a degenerative neuromuscular disorder. OPMD is characterized by muscle weakness affecting various areas, including the eyelids, throat, shoulders, hips, and leg muscles, commonly referred to as limb-girdle muscles. The PABPN1 gene is situated on the long (q) arm of chromosome 14 at position 11.2 (14q11.2) and encodes a protein that plays a crucial role in mRNA processing. This protein binds to the end of the mRNA molecule, facilitating the formation of a polyalanine chain consisting of 10 copies of the amino acid alanine. In individuals with OPMD, the PABPN1 gene typically exhibits an elongated (expanded) polyalanine chain, with most affected individuals having between 11 to 18 alanine copies. The length of this polyalanine chain is directly correlated with the age of onset for symptoms; for instance, individuals with 11 copies generally begin to experience symptoms around the age of 70, while those with 13 copies may show symptoms by age 60, and those with 16 to 18 copies often present symptoms by age 50. In cases where both copies of the gene are mutated, symptoms can manifest as early as age 30, leading to a range of issues including muscle weakness, nerve function disturbances, neuropathy, neurological complications, and cognitive decline. The CPT® Code 81312 specifically reports the PABPN1 gene analysis aimed at evaluating and detecting these expanded alleles.