Time-resolved fluorometry in the diagnosis of Leber hereditary optic neuroretinopathy

Rapid quantification of the heteroplasmy of mutant mitochondrial DNAs in Leber's hereditary optic neuropathy using the Invader technology

PURPOSE

To quantify the degree of heteroplasmy of a mitochondrial DNA (mtDNA) mutation in Leber's hereditary optic neuropathy (LHON) a biplex Invader assay was applied.

METHODS

To determine the optimum condition for the Invader assay, mtDNAs were assayed in various amounts of total DNA in 1-4-h incubations at 63 degrees C. To evaluate the suitability of the Invader assay to detect the three mutations, G3460A, G11778A, and T14484C, 10 ng of DNAs from 224 patients with bilateral optic atrophy was assayed. To quantify mtDNA heteroplasmy, a standard curve of known mixture ratios of mutation against calculation by the Invader assay was constructed. Seventy-two of the 224 patients had one of the three mutations, which corresponded with the mutation detected earlier by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) analysis. The percentages of mutant mtDNAs were calculated by the Invader assay in five heteroplasmic families, including 30 individuals with the G11778A mutation. The results were compared with those calculated earlier by labeled polymerase chain reaction followed by single-strand conformation polymorphism (PCR-SSCP) analysis.

RESULTS

In 1-8 ng of DNA, the fluorescence intensity increased near linearly during a 4-h assay. With more than 16 ng of DNA, the intensities were saturated even at the 2-h assay. A linear relationship was observed between the results obtained from separate mixtures and from the Invader assay analysis. Because two fluorescent intensities are not always the same, one of the two intensities was modified to adjust to that of the other. Complete concordance was observed between PCR-RFLP analysis and Invader assay genotyping for the 224 patients. Results of percentage of heteroplasmy in five LHON families obtained by the Invader assay were consistent with those by the PCR-SSCP analysis.

CONCLUSIONS

Invader assay is a simple, rapid, and reliable method of genotyping mtDNA mutations as well as quantifying heteroplasmy simultaneously under optimum conditions.

Quantification of parathyroid hormone-related protein mRNA by competitive PCR and time-resolved lanthanide fluorometry

Using dissociation and enhancement time-resolved lanthanide fluorometry, we have developed a quantitative competitive (QC)-PCR for measuring parathyroid hormone-related protein (PTHrP) mRNA after reverse transcription. A cloned PTHrP cDNA target was also modified by deletion of 10 bp and insertion of 21 bp in the midregion of the fragment and cloned for use as a competitor (i.e., internal standard). Two primers spanning 362 bp of target and 373 bp of competitor were designed and one of the primers was biotinylated. Two oligonucleotide probes, one recognizing the target and the other hybridizing to the competitor, were labeled with Eu chelate. Two equal aliquots of PCR products were assayed with each probe separately in streptavidin-coated wells. After 35 PCR cycles, the competitor signal decreased exponentially (y = e(3.74 −0.624x); r2 = 0.965) and the target signal increased exponentially (y = e(1.14 + 0.497x); r2 = 0.984) when 1000 copies/tube of the competitor and 0–100 000 copies/tube of the target DNA were added. Log-transformed data for the ratio of target to competitor signals (y) and the copies of the target DNA added (x) were used for plotting the linear calibration curve (y = 2.79+2.76x; r2 = 0.976). This QC-PCR enables analysis of multiple samples simultaneously and can be used to study PTHrP gene expression in malignancy and physiology.

Multiplex fluorescence-based primer extension method for quantitative mutation analysis of mitochondrial DNA and its diagnostic application for Alzheimer's disease

A sensitive and highly reproducible multiplexed primer extension assay is described for quantitative mutation analysis of heterogeneous DNA populations. Wild-type and mutant target DNA are simultaneously probed in competitive primer extension reactions using fluorophor-labeled primers and high fidelity, thermostable DNA polymerases in the presence of defined mixtures of deoxy- and dideoxynucleotides. Primers are differentially extended and the resulting products are distinguished by size and dye label. Wild-type:mutant DNA ratios are determined from the fluorescence intensities associated with electrophoretically resolved reaction products. Multiple nucleotide sites can be simultaneously interrogated with uniquely labeled primers of different lengths. The application of this quantitative technique is shown in the analysis of heteroplasmic point mutations in mitochondrial DNA that are associated with Alzheimer's disease.

Ophthalmologic findings in Leber hereditary optic neuropathy, with special reference to mtDNA mutations

BACKGROUND

Leber hereditary optic neuropathy (LHON) is associated with primary and secondary mutations in mitochondrial DNA. Clinical studies suggest that there is a wide spectrum of clinical expression.

METHODS

Fifty-three affected and 131 unaffected maternal relatives from 21 pedigrees with LHON were studied neuro-ophthalmologically and followed over a period of 14 years. Mitochondrial DNA analysis was performed on their blood specimens.

RESULTS

Thirty-two affected (60%) individuals from ten families harbored the 11778 mutation and ten individuals (19%) from three families harbored the 3460 mutation. No confirmed primary mutation was detected in 11 (21%) affected individuals from eight families. The visual outcome was better in families with the 3460 mutation than in those with the 11778 mutation. Secondary mutations did not affect the penetrance or the visual outcome. Fifteen patients had a favorable outcome; seven of whom had subclinical disease, two had slowly progressive LHON with a favorable visual outcome, and six had classic LHON with spontaneous recovery. In seven patients, the onset of the disease had been in childhood. These patients had a more favorable prognosis than the adults. Results of eye examinations of asymptomatic maternal relatives showed subclinically affected individuals.

CONCLUSIONS

In addition to classic LHON, the disease can manifest itself in three different atypical forms: subclinical disease, slowly progressive LHON with a favorable visual outcome, and LHON with the classic acute stage but spontaneous visual recovery. The current study suggests that the ophthalmologic findings and outcome in LHON are independent of secondary mutations.