Myoclonic Epilepsy and Ragged-Red Fiber Disease (MERRF): Targeted Mutation Analysis

Condition Description

Myoclonic Epilepsy & Ragged-Red Fiber Disease (MERRF) usually presents during childhood and is characterized by myoclonus, epilepsy, ataxia, and the appearance of ragged-red fibers on muscle biopsy. Other common symptoms include hearing loss, peripheral neuropathy, dementia, short stature, optic atrophy, cardiomyopathy, and exercise intolerance. Symptoms may worsen during times of stress or illness. Two mutations the mitochondrial tRNA Lys gene account for about 90% of mutations in patients with MERRF. The most common MERRF mutation, present in over 80% of patients with typical findings, is a heteroplasmic 8344A>G transition. A second mutation, 8356T>C, is present in less than 10% of patients. Heteroplasmy (the presence of both normal and rearranged mitochondrial DNA molecules) and tissue distribution of abnormal mitochondria (replicative segregation) can result in variability of clinical symptoms. Mitochondrial tRNA Lys gene mutations result in multiple mitochondrial respiratory chain deficiencies. Enzyme deficiencies, which are most pronounced in complex I and complex IV, are secondary to defects in mitochondrial protein synthesis caused by mutations in tRNA Lys. MERRF caused by mtDNA mutations is maternally inherited. It is estimated that approximately 80% of patients have a family history of the disorder.

References:

Genes (1)

tRNA Lys

Indications

  • Patients with a confirmed or suspected diagnosis of MERRF disease
  • Family members of an affected patient who are at risk for MERRF disease

Methodology

Presence or absence of two mutations (8344A>G / 8356T>C) are detected by Sanger sequencing.

Detection and Reference Range

Detection

Approximately 85-90% of patients with MERRF have mitochondrial mutations included in this panel. Over 95% of the 8344A>G and 8356T>C mutations, if present, will be detected. This assay will detect any mutation on this panel present at 15-20% heteroplasmy or greater.

Reference Range

Qualitative assay.

Specimen Requirements

When sample fails to meet the acceptable criteria, please call 470.378.2200 and ask to speak with a laboratory genetic counselor (eglgc@egl-eurofins.com).
Submit only 1 of the following specimen types
DNA, Isolated
DNA

Requirements
Microtainer
3µg
Isolation using the Perkin Elmer™Chemagen™ Chemagen™ Automated Extraction method or Qiagen™ Puregene kit for DNA extraction is recommended.
Collection and Shipping
Refrigerate until time of shipment in 100 ng/µL in TE buffer. Ship sample at room temperature with overnight delivery.
Whole Blood (EDTA)
WBP

Requirements
EDTA (Purple Top)
Infants and Young Children (<2 years of age): 2-3 ml
Children > 2 years of age to 10 years old: 3-5 ml
Older Children & Adults: 5-10 ml
Autopsy: 2-3 ml unclotted cord or cardiac blood
Collection and Shipping
Ship sample at room temperature for receipt at EGL within 24 hours of collection. Do not refrigerate or freeze.
  • MELAS (QA)may be indicated for patients who also have strokes
  • CPEO/KSS (QB) may be indicated for patients who also have progressive external ophthalmoplegia and retinopathy

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