Aminoglycoside-Induced Hearing Loss: MT-RNR1 Targeted Analysis

Turnaround Time

2 weeks

CPT Code(s)

81401

Cost

$350

Genes

• Aminoglycoside-induced hearing loss

Exposure to aminoglycoside antibiotics such as gentamycin and tobramycin can lead to sensorineural, bilateral, and severe-to-profound hearing loss. A single base-pair substitution from an A to a G at position 1555 in the MT-RNR1 gene (encoding 12S ribosomal RNA) predisposes individuals to aminoglycoside ototoxicity. Evidence has shown that even a single dose of an aminoglycoside antibiotic results in irreversible hearing loss in Individuals with this mutation. The hearing loss is not dependent on aminoglycoside exposure. Approximately 40% of individuals with the A1555G mutation who have not been treated with aminoglycosides will develop hearing loss by 30 years of age, and the penetrance increases to 80% by age 65. The MTRNR1 gene is located within mitochondrial DNA, and the A1555G mutation is, therefore, transmitted by maternal inheritance. The mutation occurs as a homoplasmic change and has a prevalence of approximately 1% in the U.S. population.

Molecular testing is useful to confirm the diagnosis and to identify the disease causing mutations within a family to allow for carrier testing and prenatal diagnosis.

The preferred sample type is 3-5 ml of peripheral blood collected in an EDTA (purple top) tube. Extracted DNA, dried blood spots, and saliva are also accepted for this test. Saliva samples must be submitted in an approved saliva kit. Contact the lab to receive a saliva kit or to have one sent to your patient.

The specimen should be kept at room temperature and delivered via overnight shipping. If shipment is delayed by one or two days, the specimen should be refrigerated and shipped at room temperature. Do not freeze the specimen. Samples collected on Friday can be safely designated for Monday delivery.

Prenatal diagnosis is available if the familial mutations are known. Additional fees for cell culture and maternal cell contamination may apply. Maternal cell contamination studies are required for all prenatal molecular tests. Contact the laboratory prior to sending a prenatal specimen.