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 MTRN1 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 MTRN1
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.
Specimen requirements: 5 to 10 ml of peripheral blood collected in an EDTA (lavender top)
Vacutainer tube is preferred. The minimal blood needed for reliable DNA
isolation is 3 ml. If necessary, ACD solution A Vacutainer tubes (yellow top)
may be submitted. Please contact the laboratory for more information.
Transport:
Please contact the Molecular Diagnostic Lab Coordinator (1-800-473-9411) for
shipping information. The specimen should be kept at room temperature and
delivered via overnight shipping. FedEx is preferred. 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.
Analysis standards: Analysis will be complete within 2 weeks of sample receipt. The
lab director assesses the quality and interpretation of results. Technical staff
members independently assess the quality and interpretation of the test. The
Greenwood Genetic Center Molecular Diagnostic Laboratory is CLIA certified and
actively participates in CAP proficiency surveys.
Reporting of Test Results: Test results with interpretation will be mailed and/or faxed
following completion of the test. Verbal reports will be telephoned to the
person(s) requesting the test when an abnormal test result occurs. Consultation
with the laboratory director and explanations of testing protocols will be
supplied upon request.
CPT Codes: 83898, 83912, 83890 |
