A Combined Nucleic Acid and Protein Analysis in Friedreich Ataxia: Implications for Diagnosis, Pathogenesis and Clinical Trial Design

PLoS ONE 6(3): e17627. doi:10.1371/journal.pone.0017627

Francesco Saccà1*, Giorgia Puorro1, Antonella Antenora1, Angela Marsili1, Alessandra Denaro1, Raffaele Piro1, Pierpaolo Sorrentino1, Chiara Pane1, Alessandra Tessa2, Vincenzo Brescia Morra1, Sergio Cocozza3, Giuseppe De Michele1, Filippo M. Santorelli2, Alessandro Filla1

1 Department of Neurological Sciences, University Federico II, Naples, Italy, 2 Molecular Medicine, IRCCS Stella Maris, Pisa, Italy, 3 Department of Cellular and Molecular Biology, University Federico II, Naples, Italy

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Methodology/Principal Findings

We enrolled 24 patients with classic FRDA phenotype (cFA), 6 late onset FRDA (LOFA), all homozygous for GAA expansion, 5 pFA cases who harbored the GAA expansion in compound heterozygosis with FXN point mutations (namely, p.I154F, c.482+3delA, p.R165P), 33 healthy expansion carriers, and 29 healthy controls. DNA was genotyped for GAA expansion, mRNA/FXN was quantified in real-time, and frataxin protein was measured using lateral-flow immunoassay in peripheral blood mononuclear cells (PBMCs). Mean residual levels of frataxin, compared to controls, were 35.8%, 65.6%, 33%, and 68.7% in cFA, LOFA, pFA and healthy carriers, respectively. Comparison of both cFA and pFA with controls resulted in 100% sensitivity and specificity, but there was overlap between LOFA, carriers and controls. Frataxin levels correlated inversely with GAA1 and GAA2 expansions, and directly with age at onset. Messenger RNA expression was reduced to 19.4% in cFA, 50.4% in LOFA, 52.7% in pFA, 53.0% in carriers, as compared to controls (p<0.0001). mRNA levels proved to be diagnostic when comparing cFA with controls resulting in 100% sensitivity and specificity. In cFA and LOFA patients mRNA levels correlated directly with protein levels and age at onset, and inversely with GAA1 and GAA2.
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