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Analysis of mutations in AARS2 in a series of CSF1R-negative patients with adult-onset leukoencephalopathy with axonal spheroids and pigmented glia

Analysis of mutations in AARS2 in a series of CSF1R-negative patients with adult-onset leukoencephalopathy with axonal spheroids and pigmented glia
Analysis of mutations in AARS2 in a series of CSF1R-negative patients with adult-onset leukoencephalopathy with axonal spheroids and pigmented glia

Importance: Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) is a frequent cause of adult-onset leukodystrophy known to be caused by autosomal dominant mutations in the CSF1R (colony-stimulating factor 1) gene. The discovery that CSF1R mutations cause ALSP led to more accurate prognosis and genetic counseling for these patients in addition to increased interest in microglia as a target in neurodegeneration. However, it has been known since the discovery of the CSF1R gene that there are patients with typical clinical and radiologic evidence of ALSP who do not carry pathogenic CSF1R mutations. These patients include those in whom the pathognomonic features of axonal spheroids and pigmented microglia have been found. Achieving a genetic diagnosis in these patients is important to our understanding of this disorder.

Objective: To genetically characterize a group of patients with typical features of ALSP who do not carry CSF1R mutations.

Design, Settings, and Participants: In this case series study, 5 patients from 4 families were identified with clinical, radiologic, or pathologic features of ALSP in whom CSF1R mutations had been excluded previously by sequencing. Data were collected between May 2014 and September 2015 and analyzed between September 2015 and February 2016.

Main Outcomes and Measures: Focused exome sequencing was used to identify candidate variants. Family studies, long-range polymerase chain reaction with cloning, and complementary DNA sequencing were used to confirm pathogenicity.

Results: Of these 5 patients, 4 were men (80%); mean age at onset of ALSP was 29 years (range, 15-44 years). Biallelic mutations in the alanyl-transfer (t)RNA synthetase 2 (AARS2) gene were found in all 5 patients. Frameshifting and splice site mutations were common, found in 4 of 5 patients, and sequencing of complementary DNA from affected patients confirmed that the variants were loss of function. All patients presented in adulthood with prominent cognitive, neuropsychiatric, and upper motor neuron signs. Magnetic resonance imaging in all patients demonstrated a symmetric leukoencephalopathy with punctate regions of restricted diffusion, typical of ALSP. In 1 patient, brain biopsy demonstrated axonal spheroids and pigmented microglia, which are the pathognomonic signs of ALSP.

Conclusions and Relevance: This work indicates that mutations in the tRNA synthetase AARS2 gene cause a recessive form of ALSP. The CSF1R and AARS2 proteins have different cellular functions but overlap in a final common pathway of neurodegeneration. This work points to novel targets for research and will lead to improved diagnostic rates in patients with adult-onset leukoencephalopathy.

2168-6149
1433-1439
Lynch, David S.
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Zhang, Wei Jia
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Lakshmanan, Rahul
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Kinsella, Justin A.
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Uzun, Günes Altiokka
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Karbay, Merih
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Tüfekçioglu, Zeynep
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Hanagasi, Hasmet
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Burke, Georgina
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Foulds, Nicola
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Hammans, Simon R.
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Bhattacharjee, Anupam
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Wilson, Heather
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Adams, Matthew
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Walker, Mark
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Nicoll, James A.R.
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Chataway, Jeremy
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Fox, Nick
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Davagnanam, Indran
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Phadke, Rahul
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Houlden, Henry
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Lynch, David S.
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Zhang, Wei Jia
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Lakshmanan, Rahul
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Kinsella, Justin A.
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Uzun, Günes Altiokka
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Karbay, Merih
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Tüfekçioglu, Zeynep
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Hanagasi, Hasmet
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Burke, Georgina
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Foulds, Nicola
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Hammans, Simon R.
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Bhattacharjee, Anupam
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Wilson, Heather
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Adams, Matthew
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Walker, Mark
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Nicoll, James A.R.
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Chataway, Jeremy
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Fox, Nick
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Davagnanam, Indran
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Phadke, Rahul
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Houlden, Henry
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Lynch, David S., Zhang, Wei Jia, Lakshmanan, Rahul, Kinsella, Justin A., Uzun, Günes Altiokka, Karbay, Merih, Tüfekçioglu, Zeynep, Hanagasi, Hasmet, Burke, Georgina, Foulds, Nicola, Hammans, Simon R., Bhattacharjee, Anupam, Wilson, Heather, Adams, Matthew, Walker, Mark, Nicoll, James A.R., Chataway, Jeremy, Fox, Nick, Davagnanam, Indran, Phadke, Rahul and Houlden, Henry (2016) Analysis of mutations in AARS2 in a series of CSF1R-negative patients with adult-onset leukoencephalopathy with axonal spheroids and pigmented glia. JAMA Neurology, 73 (12), 1433-1439. (doi:10.1001/jamaneurol.2016.2229).

Record type: Article

Abstract

Importance: Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) is a frequent cause of adult-onset leukodystrophy known to be caused by autosomal dominant mutations in the CSF1R (colony-stimulating factor 1) gene. The discovery that CSF1R mutations cause ALSP led to more accurate prognosis and genetic counseling for these patients in addition to increased interest in microglia as a target in neurodegeneration. However, it has been known since the discovery of the CSF1R gene that there are patients with typical clinical and radiologic evidence of ALSP who do not carry pathogenic CSF1R mutations. These patients include those in whom the pathognomonic features of axonal spheroids and pigmented microglia have been found. Achieving a genetic diagnosis in these patients is important to our understanding of this disorder.

Objective: To genetically characterize a group of patients with typical features of ALSP who do not carry CSF1R mutations.

Design, Settings, and Participants: In this case series study, 5 patients from 4 families were identified with clinical, radiologic, or pathologic features of ALSP in whom CSF1R mutations had been excluded previously by sequencing. Data were collected between May 2014 and September 2015 and analyzed between September 2015 and February 2016.

Main Outcomes and Measures: Focused exome sequencing was used to identify candidate variants. Family studies, long-range polymerase chain reaction with cloning, and complementary DNA sequencing were used to confirm pathogenicity.

Results: Of these 5 patients, 4 were men (80%); mean age at onset of ALSP was 29 years (range, 15-44 years). Biallelic mutations in the alanyl-transfer (t)RNA synthetase 2 (AARS2) gene were found in all 5 patients. Frameshifting and splice site mutations were common, found in 4 of 5 patients, and sequencing of complementary DNA from affected patients confirmed that the variants were loss of function. All patients presented in adulthood with prominent cognitive, neuropsychiatric, and upper motor neuron signs. Magnetic resonance imaging in all patients demonstrated a symmetric leukoencephalopathy with punctate regions of restricted diffusion, typical of ALSP. In 1 patient, brain biopsy demonstrated axonal spheroids and pigmented microglia, which are the pathognomonic signs of ALSP.

Conclusions and Relevance: This work indicates that mutations in the tRNA synthetase AARS2 gene cause a recessive form of ALSP. The CSF1R and AARS2 proteins have different cellular functions but overlap in a final common pathway of neurodegeneration. This work points to novel targets for research and will lead to improved diagnostic rates in patients with adult-onset leukoencephalopathy.

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Accepted/In Press date: 12 May 2016
e-pub ahead of print date: 17 October 2016
Published date: 1 December 2016

Identifiers

Local EPrints ID: 413545
URI: https://eprints.soton.ac.uk/id/eprint/413545
ISSN: 2168-6149
PURE UUID: 187647e8-fe4d-4b07-b4a6-23dfb6923a29
ORCID for James A.R. Nicoll: ORCID iD orcid.org/0000-0002-9444-7246

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Date deposited: 25 Aug 2017 16:31
Last modified: 10 Dec 2019 01:47

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Contributors

Author: David S. Lynch
Author: Wei Jia Zhang
Author: Rahul Lakshmanan
Author: Justin A. Kinsella
Author: Günes Altiokka Uzun
Author: Merih Karbay
Author: Zeynep Tüfekçioglu
Author: Hasmet Hanagasi
Author: Georgina Burke
Author: Nicola Foulds
Author: Simon R. Hammans
Author: Anupam Bhattacharjee
Author: Heather Wilson
Author: Matthew Adams
Author: Mark Walker
Author: Jeremy Chataway
Author: Nick Fox
Author: Indran Davagnanam
Author: Rahul Phadke
Author: Henry Houlden

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