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Hereditary Hearing Loss: Mitochondrial
Gene Analysis (A1555G)
About 1 in 1000 young children have a major hearing impairment (threshold
>80dB). Aminoglycoside-induced, and nonsyndromic sensorineural
deafness have been associated in some cases with an A1555G mutation in the
mitochondria (12S DNA). The deafness can have either a congenital or late onset
presentation, and affected individuals may not have been exposed to the
antibiotic. The significance of the mutation is not fully understood but aminoglycoside antibiotics in high concentrations have an ototoxic affect by
damaging the auditory hair cells in the cochlea. The incidence of this
mutation is not well known but may represent a small percentage
of affected individuals that show no signs of Connexin 26 defects. In maternally
inherited forms of hearing loss the incidence of the mutation
may be far greater.
REASONS FOR REFERRAL:
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To determine whether a hearing defect in a child is hereditary.
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To evaluate the risk of having a child with hearing loss.
- To determine the genetic
basis for hearing loss in an affected individual, in order to
modify therapy.
- Individuals at risk who wish prenatal
diagnosis.
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For ambiguous patients this
test is often included with testing for
Connexin 26 and
Connexin 30.
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TESTING METHODOLOGY:
- PCR amplification
of the mitochondrial DNA followed by mutation specific restriction enzyme
digestion for mtA1555G mutation.
SPECIMEN REQUIREMENTS:
- Blood EDTA (purple top) tubes:
Newborn: minimum 1-2 mL
Child/Adult: prefer 2 tubes of 3-5 mL
- Prenatal testing: Please contact the
laboratory for instructions.
TURNAROUND TIME: 8
working days
CPT CODES:
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