CPT® Code 81326

PMP22 (peripheral myelin protein 22) (eg, Charcot-Marie-Tooth, hereditary neuropathy with liability to pressure palsies) gene analysis; known familial variant

Molecular genetic testing is a critical procedure used to identify specific mutations in the peripheral myelin protein 22 (PMP22) gene, which is associated with Charcot-Marie-Tooth disease and hereditary neuropathy with liability to pressure palsies. The PMP22 gene is located on chromosome 17 and encodes a protein that is essential for the formation and maintenance of the myelin sheath surrounding nerve cells. This myelin sheath is crucial for the proper transmission of electrical impulses along the nerves, which are facilitated by Schwann cells that produce and maintain this protective covering. Mutations in the PMP22 gene can lead to various forms of neuropathy, with inheritance patterns that can be either autosomal recessive—where two mutated copies of the gene are required for the disease to manifest—or autosomal dominant, where a single mutated copy is sufficient to cause the condition. The most prevalent form of Charcot-Marie-Tooth disease, known as Type 1A, is characterized by a duplication of the PMP22 gene, resulting in an overproduction of the PMP22 protein. This overproduction disrupts the normal processing of the protein, leading to a reduction in functional PMP22 levels, which in turn decreases the integrity of the myelin sheath. The resultant impairment of Schwann cell function can lead to decreased muscle activation and impaired nerve signal transmission. Other mutations may involve deletions or alterations in the amino acid sequence of the PMP22 gene, which can also adversely affect Schwann cell function and contribute to demyelination. Hereditary neuropathy with liability to pressure palsies is typically associated with a reduction in gene dosage, where one copy of the PMP22 gene is lost, leading to insufficient levels of PMP22 in circulation. This condition may also arise from mutations that produce a smaller, unstable protein that degrades rapidly, leaving the myelin sheath vulnerable to damage from external pressure. The testing for known familial variants, such as Type 1E of Charcot-Marie-Tooth disease, is essential for accurate diagnosis and management. Type 1E is notably characterized by sensorineural hearing loss and is often caused by a specific mutation that replaces the amino acid alanine with proline at position 67 (Ala67Pro). This comprehensive understanding of the PMP22 gene and its mutations is vital for effective genetic counseling and patient management.