MT-ND4 m.11232T>C Targeted Variant Analysis

Clinical Information

The MT-ND4 m.11232T>C variant has recently been associated with severe neurologic complications following general anesthesia, particularly after exposure to volatile anesthetic agents such as sevoflurane. The variant has been reported predominantly in the homoplasmic state among affected individuals from the Venezuelan-associated maternal lineage. Affected individuals are often clinically asymptomatic prior to anesthetic exposure but may develop acute neurologic deterioration characterized by encephalopathy, metabolic acidosis, hyperlactatemia, and basal ganglia injury following anesthesia. Identification of the m.11232T>C variant may therefore aid in risk assessment and perioperative management of individuals with Venezuelan maternal ancestry.

Technical Information

• This targeted testing is performed by Sanger sequencing.
• Variants with a mutant heteroplasmy 20% or lower may not be detected by Sanger. Additionally, levels of mutant heteroplasmy above 80% may appear homoplasmic by Sanger sequencing. As heteroplasmy levels vary from tissue to tissue, a negative blood test cannot completely rule out the chance that an individual carries a mtDNA variant that is either at very low heteroplasmy levels in blood or present in a different tissue type.

Specimen Requirements

• The preferred sample type is 3-5 mL of peripheral blood collected in an EDTA (purple top) tube. Dried blood spots, extracted DNA, solid tissue, and saliva are also accepted for this test. Blood and saliva kits are available upon request.
• Approximately 75 µL of blood should be applied to each of the five circles on a filter paper dried blood spot card. Allow blood to dry for at least 4 hours before shipping.
• Send approximately 5µg of extracted DNA at a requested concentration of 90-130 ng/µL.
• Solid tissue should be placed in screw-capped, sterile container with sterile media or alternatively Hank’s balanced salt solution, or physiologically normal saline.
• Saliva samples must be submitted in an approved saliva kit.

Transport Instructions

• The blood specimen should be kept at room temperature and delivered via overnight shipping. If shipment is delayed by one or two days, the specimen should be refrigerated and shipped at room temperature. Samples collected on Friday can be safely designated for Monday delivery.
• DBS cards should be shipped at room temperature.
• Extracted DNA should be sent at room temperature via overnight delivery.
• Solid tissue should be kept at room temperature if transported immediately. If the specimen is not being immediately transported to the laboratory, it may be refrigerated. The sample should be sent by courier or overnight mail to arrive at the laboratory within 24 hours.
• Saliva is stable at room temperature and can be delivered via overnight or ground shipping.