Abstract
Background
Dementia with Lewy bodies (DLB) is the second most common neurodegenerative dementia affecting the elderly. The GGGGCC hexanucleotide expansion mutation at the C9orf72 locus has been identified as a major cause of amyotrophic lateral sclerosis and frontotemporal dementia, raising the question of whether this mutation is a factor in DLB. Furthermore, a small number of clinically diagnosed DLB patients have previously been reported to carry the pathologic C9orf72 hexanucleotide repeat expansion.
Objective
To explore whether the C9orf72 mutation is present in pathologically confirmed DLB patients.
Methods
We screened a cohort of 111 definite DLB cases with extensive Lewy body pathology for the C9orf72 hexanucleotide repeat expansion using the repeat-primed polymerase chain reaction assay.
Results
No pathogenic expansions of the C9orf72 hexanucleotide repeat were found, suggesting that there is no causal relationship between C9orf72 and DLB.
Conclusion
Our data illustrate that C9orf72 screening of clinically diagnosed DLB patients should only be considered in cases with a family history of motor neuron disease or frontotemporal dementia to distinguish between mimic diseases.
Keywords: Dementia with Lewy bodies, amyotrophic lateral sclerosis, frontotemporal dementia, C9orf72, hexanucleotide repeat expansion
INTRODUCTION
Dementia with Lewy bodies (DLB) is a degenerative neurological disorder clinically characterized by a combination of progressive cognitive impairment, altered mental status, neuroleptic sensitivity, visual hallucinations, and parkinsonism.[1] DLB is the second most prevalent neurodegenerative dementia in the elderly population next to Alzheimer's disease, accounting for approximately 20 percent of cases.[2] The molecular mechanism of DLB is largely unknown, although a genetic component has been proposed.[3]
A [GGGGCC]n hexanucleotide expansion at the C9orf72 locus is the most common genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia.[4, 5] This repeat expansion has also been identified in clinically diagnosed patients with Alzheimer's disease, atypical parkinsonism or psychosis.[6-8] Psychosis is a common symptom in DLB, raising the question of whether the C9orf72 hexanucleotide expansion is a genetic factor in DLB. Previous clinical studies have considered this question[9-12], with one study reporting two out of 102 clinically diagnosed DLB patients having a pathogenic repeat expansion.[10] However, the clinical diagnosis of DLB is challenging with a high false positive rate due to mimic syndromes.[13, 14] As a consequence, the research community is increasingly relying on specimens that are pathologically confirmed as this represents the gold standard for diagnosis. To investigate if C9orf72 repeat expansions have a role in pathologically confirmed DLB, we conducted a genetic screening study on a cohort of 111 definite DLB cases.
METHODS
A total of 111 pathologically confirmed DLB cases from the Johns Hopkins Morris K. Udall Center for Parkinson's Disease Research Center of Excellence and the Johns Hopkins Alzheimer Disease Research Center were studied. The cohort included neocortical cases (n=86) and transitional-type DLB cases (n=25) diagnosed using the McKeith criteria.[15] All subjects were Caucasian, with males representing 67 percent of cases. The average age of death was 78 (range: 57 – 94) years. The majority of patients (66%) also met pathological criteria for Alzheimer disease. Additional clinicopathological characteristics are displayed in Table 1. DNA was extracted from frozen brain sections using the Qiagen DNeasy extraction protocol (Qiagen, Hilden, Germany). The hexanucleotide repeat at the C9orf72 locus was genotyped using the repeat-primed polymerase chain reaction assay as previously described.[4] The resulting PCR amplicons were analyzed on an Applied Biosystems 3730xl DNA Analyzer (Life Technologies, Grand Island, NY, USA). A pathologic expansion was defined as over 30 GGGGCC repeats.[4]
Table 1.
Clinical characteristics for 111 pathologically confirmed DLB cases
| Pathologic Diagnosis | n | % Male | Age at Onset (Range) | Age at Death (Range) | Disease Duration (Range) | Family History (%) | Clinical Diagnosis |
DLB subtype |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| AD | PD | AD/PD | FTD | PDD | DLB | Other | Neocortical | Limbic | |||||||
| Pure DLB | 27 | 85 | 60 (40 - 79) | 76 (60 - 84) | 16 (3 - 33) | 6 (22) | 0 | 2 | 2 | 0 | 20 | 3 | 0 | 18 | 9 |
| DLB/AD | 73 | 60 | 66 (42 - 87) | 78 (57 - 94) | 12 (2 - 30) | 23 (32) | 12 | 4 | 1 | 2 | 37 | 8 | 9 | 63 | 10 |
| DLB/other | 11 | 64 | 68 (43 - 83) | 82 (64 - 89) | 14 (6 - 27) | 4 (36) | 1 | 2 | 0 | 0 | 8 | 0 | 0 | 5 | 6 |
| Total | 111 | 67 | 65 (40 - 87) | 78 (57 - 94) | 13 (2 - 33) | 33 (30) | 13 | 8 | 3 | 2 | 65 | 11 | 9 | 86 | 25 |
Clinical data of the pathology confirmed cohort is grouped by pathology type. Clinical diagnosis and extent of Lewy body pathology is presented. Family history was positive if the patient reported at least one first- or second-degree relative with dementia, cognitive impairment, parkinsonism, Dementia with Lewy bodies, Parkinson disease, or Alzheimer dementia. Abbreviations: AD, Alzheimer disease; DLB, Dementia with Lewy bodies; FTD, Frontotemporal dementia; PD, Parkinson disease; PDD, Parkinson disease dementia
RESULTS
We observed hexanucleotide repeats of less than 20 in our cohort, which is considered normal. None of the 111 pathologically confirmed cases carried a pathogenic C9orf72 repeat expansion.
DISCUSSION
This study shows that the pathogenic C9orf72 expansion is not present in pathologically confirmed Caucasian DLB patients. In a large screening study of familial Alzheimer dementia cases, Harms et al. identified an Alzheimer dementia patient with a pathological C9orf72 repeat expansion. [16] Interestingly, this case was also found to have neocortical Lewy bodies in addition to typical Alzheimer pathology. However, tissue was not available for evaluation of pathologic changes consistent with frontotemporal dementia. It is possible the pathologic C9orf72 mutation in this patient was coincidental and this patient could have had frontotemporal dementia in addition to Alzheimer dementia. Cases of frontotemporal lobar degeneration with motor neuron disease can present with symptoms mimicking DLB.[13] Our data suggest that the presence of a pathological C9orf72 hexanucleotide expansion in a clinically diagnosed DLB case likely represents an atypical presentation of frontotemporal dementia. Thus, C9orf72 expansion screening should only be considered for DLB patients with a family history of either motor neuron disease or frontotemporal dementia. In this situation genetic testing provides a method to help distinguish among intersecting clinical syndromes.
ACKNOWLEDGEMENTS
Technical support: The authors thank Ms. Gay Rudow for performing DNA extractions from brain tissue.
Funding: J.T.G., K.C.A., and S.W.S report that this work was supported (in part) by the Intramural Research Program of the US National Institutes of Health (National Institute on Aging, National Institute of Neurological Disorders and Stroke) (Z01-AG000949). K.C.A. reports that this research was also made possible through the NIH Medical Research Scholars Program, a public-private partnership supported jointly by the NIH and generous contributions to the Foundation for the NIH from the Doris Duke Charitable Foundation, the Howard Hughes Medical Institute, the American Association for Dental Research, the Colgate-Palmolive Company, and other private donors. For a complete list, visit the foundation website at http://www.fnih.org. S.W.S. received a R25 career development grant by the National Institute of Neurological Disorders and Stroke (R25 NS065729). DNA from brain tissue samples was provided by the Johns Hopkins Morris K. Udall Center for Parkinson's Disease Research Center of Excellence (NIH P50 NS38377) and the Johns Hopkins Alzheimer Disease Research Center (NIH P50 AG05146). T.M.D. is the Leonard and Madlyn Abramson Professor in Neurodegenerative Disease.
Footnotes
CONFLICTS OF INTEREST
The authors declare no conflicts of interest.
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