A False-Positive Diagnosis for the Common MELAS (A3243G) Mutation Caused by a Novel Variant (A3426G) in the ND1 Gene of Mitochondria DNA.

Background

Several mutations in mitochondrial DNA (mtDNA) are associated with the syndrome of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). The "common" MELAS mutation, A3243G in the tRNA leucine (UUR) gene, affects approximately 80% of cases and is associated with respiratory chain complex I deficiency. Methods and

Results

The A3243G mutation creates an ApaI restriction endonuclease site and can be detected by polymerase chain reaction (PCR) amplification of a region of mtDNA containing nt 3243, followed by ApaI digestion and electrophoretic analysis of the resulting fragments. Analysis of mtDNA from a child with complex I deficiency indicated the presence of the mutation homoplasmically in heart, liver, and skeletal muscle. Sequencing revealed only normal tRNA leucine (UUR) sequence, and a novel variant at nt 3426 in the ND1 subunit of complex I, which creates an ApaI site. ApaI digestion results in fragments of similar size to those found in patients with the A3243G mutation.

Conclusions

A novel variant at nt 3426 of mtDNA creates an ApaI site and can potentially cause a false-positive result for the presence of the A3243G mutation. Given the highly polymorphic nature of mtDNA, care must be exercised in choosing primers for restriction endonuclease-based diagnostic tests for point mutations, and confirmation of a mutation by an independent method is recommended.