Saint Francis Health System

Mitochondrial Hearing Loss - Mutation MT A1555G

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MITOCHONDRIAL HEARING LOSS - MUTATION mt A1555G 

 

Gene Symbol: MT-RNR1 (12S rRNA)

TURNAROUND TIME: 8 business days

 TESTING METHODOLOGY: Detection of the mt.1555A>G mutation by PCR and restriction enzyme digestion.

SPECIMEN REQUIREMENTS:

  • Collect: Prefer two 5ml whole blood EDTA (lavender top) tube.
  • Min. Collection: 0.7 ml whole blood EDTA.
  • Transport: blood EDTA at Room Temp shipped regular next day air (No Saturday delivery; store specimen at 40°C and ship Monday).
  • Stability: Ambient: up to 7 days; Refrigerated: 2 weeks. Frozen: unacceptable
  • Unacceptable Conditions: Serum. Frozen or severely hemolyzed blood. Clotted blood.
  • Prenatal testing: Direct: 5ml direct unspun amniotic fluid or 15mg CVS tissue with a backup flask growing. Culture: confluent T25 flask. Maternal blood sample is required for maternal cell contamination studies.

A Molecular Genetics Laboratory Test Requisition must accompany the specimen. Contact the Molecular Laboratory at 918-502-1721 to obtain further information.

Note:
Counseling and informed consent are recommended for genetic testing; Center for Genetic Testing at Saint Francis consent form is available as a resource but not required.
 
INTERPRETATIVE DATA:
 
Incidence: Not well known and varies by ethnicity. May represent a small percentage of individuals with Non-Syndromic Hearing Loss (NSHL) that show no signs of Connexin 26 defects.
Inheritance: Maternal
 
Disease Characteristics: Moderate to profound late onset, or aminoglycoside induced NSHL
Molecular Genetic Mechanism: The mt.1555A>G mutation in the mitochondrial genome has been associated with predisposition to aminoglycoside ototoxicity and/or late-onset sensorineural hearing loss. Roughly 70% of cases of mitochondrial hearing loss are due to mutations in the MT-RNR1 gene.
 
 
Clinical Sensitivity: 70%
 
Analytical Sensitivity: 99%
 
Test Limitations: mutations present in less than 30% of the mitochondrial genomes may not be detected.

INDICATIONS FOR USE:

  • Moderate to profound hearing loss
  • Family history of hearing loss suggestive of maternal inheritance
  • Hearing loss following known aminoglycoside exposure
  • Known familial mutation
  • Relatives of an affected individual that may be at risk for aminoglycoside ototoxicity.

ADDITIONAL RESOURCES:

OMIM MT-RNR1 - www.omim.org/entry/561000 
OMIM Aminoglycoside-Induced Deafness - www.omim.org/entry/580000 
Genetics Home Reference: www.ghr.nlm.nih.gov/gene/MT-RNR1 
Gene Reviews: www.ncbi.nlm.nih.gov/books/NBK1422