MTTL1
The Clinical Diagnostics Service of the Molecular Otolaryngology Research Laboratory is a Joint Commission-approved CLIA-accredited diagnostic laboratory that offers mutation screening of several genes.

MTTL1 (OMIM# 590050)
The A3243G mutation 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 mutation also causes MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) (OMIM# 540000). MORL offers screening for this mutation.

MORL screening methodology
Following sample amplification with oligonucleotide primers within the MTTL1 gene, a restriction digest is completed; digestion products are resolved by agarose gel electrophoresis. Presence of the A3243G mutation creates an additional ApaI restriction site.

Sensitivity
Sensitivity is greater than 99%.

Turn-around time
Turn around time is approximately 3 months.

Cost: $150

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

GeneTests  GeneReviews – Nonsyndromic Hearing Loss, Mitochondrial

References
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 
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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
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