Last Updated: January 27, 2010 |
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| Test Name
| Retinitis Pigmentosa and Ataxia (NARP) |
| Synonyms
| Neuropathy Ataxia; Retinitis Pigmentosa; |
| Test Codes
| QK |
| Condition Description
| NARP, characterized by peripheral Neuropathy, Ataxia, and Retinitis Pigmentosa, is the mild end of the Leigh disease neurodegerative spectrum. The onset of symptoms may begin in childhood, and may increase during times of illness. Other features may include, learning delay, hearing loss, short stature, progressive external ophthalmoplegia, and cardiac conduction defects. The level of heteroplasmy (meaning the presence of both normal and rearranged mitochondrial DNA molecules) as well as the type of tissue affected, influences the severity of disease. Like Leigh disease, NARP is caused by defects in mitochondrial energy production.
The 8993T>G and 8993T>C mtDNA mutations account for up to 50% of NARP mutations. The 3,243A>G mutation has been observed in patients with Leigh/NARP-like symptoms. NARP is typically associated with 70-90% heteroplasmy of mutant mitochondria. Higher levels of mtDNA mutation heteroplasmy typically result in Leigh syndrome. In some patients, mtDNA mutations are occasionally not be detectable in blood cells due to replicative segregation (uneven tissue distribution of mitochondrial molecules). For patients with a clinical diagnosis of NARP, testing for mtDNA mutations in muscle tissue may be indicated when mutations are not detected in mtDNA isolated from a blood sample.
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| Indications
| This test is indicated for:
- Patients with a confirmed/suspected diagnosis of NARP.
- Family members of an affected patient who may be at risk for NARP.
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| Related Tests
| Leigh Disease (QD) |
| Methodology
| Two mutations (8993T>G / 8993T>C) are analyzed using PCR amplification and restriction enzyme digest fragment analysis. The 3243A>G mutation is analyzed by a quantitative allele-specific extension assay. |
| Reference Ranges
| Qualitative assay. |
| Detection
| The 8993T>G and 8993T>C mutations in MTATP6 account for up to 50% of NARP mutations. Over 95% of these selected mutations will be detected by this analysis. The 3243A>G mutation can be detected at approximately 10% heteroplasmy. All other mutations will be detected at approximately 15-20% heteroplasmy. |
| Turnaround Time
| 3 weeks |
| Samples Accepted
| Monday - Friday 8:30AM - 5:00PM |
| Special Instructions
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| Requirements
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| Specimen Type |
Specimen Requirements |
Shipping |
| Blood |
Children under 1 year: Collect 1ml blood in a purple top (EDTA)/yellow top (ACD) tube.
Children over 1 year: Collect 3-5ml blood in a purple top (EDTA)/yellow top (ACD) tube.
Older children & adults: Collect 5-10ml blood in a purple top (EDTA)/yellow top (ACD) tube. |
Refrigerate sample until shipment. Send sample at room temperature with overnight delivery within 7 days of collection. |
| Tissue for mtDNA mutation study |
After biopsy, immediately freeze tissue in liquid nitrogen. 1-2 mm in length or >100 mgs is acceptable. |
Ship on dry ice. If biopsy is performed on a Friday, keep sample at -80oC or colder over the weekend and ship on Monday. |
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| CPT Codes
| 83891, 83892(x2), 83894, 83898(x2), 83912, 83914(x2) |
| Price
| $525*
*A 20% discount will apply when full payment is received with a sample.
Please contact our office for information on institutional and volume discount pricing (404-778-8580 or domgbilling@emory.edu). |
