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C9ORF72 repeat expansions in cases with previously identified pathogenic mutations
Journal article   Open access   Peer reviewed

C9ORF72 repeat expansions in cases with previously identified pathogenic mutations

Marka van Blitterswijk, Matthew C. Baker, Mariely DeJesus-Hernandez, Roberta Ghidoni, Luisa Benussi, Elizabeth Finger, Ging-Yuek R. Hsiung, Brendan J. Kelley, Melissa E. Murray, Nicola J. Rutherford, …
Neurology, v 81(15), pp 1332-1341
08 Oct 2013
PMID: 24027057
url
https://doi.org/10.1212/wnl.0b013e3182a8250cView
Published, Version of Record (VoR)Open Access (License Unspecified) Open
url
https://doi.org/10.1212/WNL.0b013e3182a8250cView
Published, Version of Record (VoR) Open

Abstract

Clinical Neurology Life Sciences & Biomedicine Neurosciences & Neurology Science & Technology
Objective: To identify potential genetic modifiers contributing to the phenotypic variability that is detected in patients with repeat expansions in chromosome 9 open reading frame 72 (C9ORF72), we investigated the frequency of these expansions in a cohort of 334 subjects previously found to carry mutations in genes known to be associated with a spectrum of neurodegenerative diseases. Methods: A 2-step protocol, with a fluorescent PCR and a repeat-primed PCR, was used to determine the presence of hexanucleotide expansions in C9ORF72. For one double mutant, we performed Southern blots to assess expansion sizes, and immunohistochemistry to characterize neuropathology. Results: We detected C9ORF72 repeat expansions in 4 of 334 subjects (1.2% [or 1.8% of 217 families]). All these subjects had behavioral phenotypes and also harbored well-known pathogenic mutations in either progranulin (GRN: p.C466LfsX46, p.R493X, p.C31LfsX35) or microtubule-associated protein tau (MAPT: p.P301L). Southern blotting of one double mutant with a p.C466LfsX46 GRN mutation demonstrated a long repeat expansion in brain (> 3,000 repeats), and immunohistochemistry showed mixed neuropathology with characteristics of both C9ORF72 expansions and GRN mutations. Conclusions: Our findings indicate that co-occurrence of 2 evidently pathogenic mutations could contribute to the pleiotropy that is detected in patients with C9ORF72 repeat expansions. These findings suggest that patients with known mutations should not be excluded from further studies, and that genetic counselors should be aware of this phenomenon when advising patients and their family members.

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Clinical Neurology
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