Citations

BACKGROUND Friedreich ataxia (FRDA) is caused by reduced frataxin (FXN) concentrations. A clinical diagnosis is typically confirmed by DNA-based assays for GAA-repeat expansions or mutations in the FXN (frataxin) gene; however, these assays are not applicable to therapeutic monitoring and population screening. To facilitate the diagnosis and monitoring of FRDA patients, we developed an immunoassay for measuring FXN. METHODS Antibody pairs were used to capture FXN and an internal control protein, ceruloplasmin (CP), in 15 μL of whole blood (WB) or one 3-mm punch of a dried blood spot (DBS). Samples were assayed on a Luminex LX200 analyzer and validated according to standard criteria. RESULTS The mean recovery of FXN from WB and DBS samples was 99%. Intraassay and interassay imprecision (CV) values were 4.9%–13% and 9.8%–16%, respectively. The FXN limit of detection was 0.07 ng/mL, and the reportable range of concentrations was 2–200 ng/mL. Reference adult and pediatric FXN concentrations ranged from 15 to 82 ng/mL (median, 33 ng/mL) for DBS and WB. The FXN concentration range was 12–22 ng/mL (median, 15 ng/mL) for FRDA carriers and 1–26 ng/mL (median 5 ng/mL) for FRDA patients. Measurement of the FXN/CP ratio increased the ability to distinguish between patients, carriers, and the reference population. CONCLUSIONS This assay is applicable to the diagnosis and therapeutic monitoring of FRDA. This assay can measure FXN and the control protein CP in both WB and DBS specimens with minimal sample requirements, creating the potential for high-throughput population screening of FRDA.

The use of valproate sodium as an antiepileptic is not advised in children with an undiagnosed metabolic condition because of the increased risk of hepatotoxicity and encephalopathy. Here the authors describe a 2.5-year-old girl with a history of developmental delay, failure to thrive, and a seizure disorder whose seizures worsened after the introduction of valproate sodium. This led to a search for an underlying metabolic disorder, and after extensive investigations, a diagnosis of nonketotic hyperglycinemia was made. In this report, the authors discuss the metabolic conditions that can be worsened by valproate sodium. Valproate sodium interferes with the glycine cleavage enzyme synthesis in the mitochondria, hence increasing glycine levels. The increased glycine levels are responsible for worsening of the underlying metabolic condition and increased seizure frequency.