PDF iconMORL 2020 Hearing Loss Test Requisition Form (Effective January 3, 2020)

The Clinical Diagnostics Service of the Molecular Otolaryngology & Renal Research Laboratories is a CLIA-approved, Joint Commission-accredited diagnostic laboratory that offers variant screening of several genes.

MTTL1 (OMIM# 590050)
The A3243G variant in the MTTL1 gene (OMIM# 590050), which encodes the mitochondrial transfer RNA for leucine, has been shown to segregate with maternally inherited diabetes mellitus, sensorineural deafness, hypertrophic cardiomyopathy and/or renal failure (Manouvrier et al., 1995.) The A3243G variant also causes MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) (OMIM# 540000). MORL offers screening for this variant.

Indications for screening
This test is appropriate for a patient suspected of having maternally inherited diabetes mellitus and sensorineural hearing loss.

Samples are amplified with an oligonucleotide primer pair that flanks the A3243G variant within the MTTL1 gene, followed by sequencing.

Sensitivity is greater than 99%.

Turnaround time
Turnaround time is approximately 3 months (Average TAT - 22 days).

Sample Required
8 - 10 cc. whole blood in lavender (EDTA) top tubes OR 10 μg DNA, minimum concentration: 50 ng/μl (A260/A280 1.8-2) resuspended in 0.1mM EDTA (10mM Tris HC1, 0.1mM EDTA, pH 8, Teknova Cat#T0220).

Cost & CPT Codes
See the MORL Testing Menu

GeneTests GeneReviews – Nonsyndromic Hearing Loss, Mitochondrial


Majamaa, K. et al.: Epidemiology of A3243G, the Mutation for Mitochondrial Encephalomyopathy, Lactic Acidosis, and Strokelike Episodes: Prevalence of the Mutation in an Adult Population. Am. J. Hum. Genet. 63:447-454, 1998.
PubMed ID: 9683591
PubMed Search

Manouvrier, S et al; Point mutation of the mitochondrial tRNA(leu) gene (A 3243 G) in maternally inherited hypertrophic cardiomyopathy, diabetes mellitus, renal failure, and sensorineural deafness. J. Med. Genet. 32: 654-656, 1995.
PubMed ID: 7473662
PubMed Search