Genetic and Clinical Features of Progranulin-Associated Frontotemporal Lobar Degeneration

doi:10.1001/archneurol.2011.53

Arch Neurol. Author manuscript; available in PMC 2012 April 1.

Published in final edited form as:

Arch Neurol. 2011 April; 68(4): 488–497.

doi: 10.1001/archneurol.2011.53

PMCID: PMC3160280

NIHMSID: NIHMS318289

Genetic and Clinical Features of Progranulin-Associated Frontotemporal Lobar Degeneration

Alice S. Chen-Plotkin, MD, Maria Martinez-Lage, MD, Patrick M. A. Sleiman, PhD, William Hu, MD, PhD, Robert Greene, BS, Elisabeth McCarty Wood, MS, Shaoxu Bing, Murray Grossman, MD, Gerard D. Schellenberg, PhD, Kimmo J. Hatanpaa, MD, PhD, Myron F. Weiner, MD, Charles L. White, III, MD, William S. Brooks, MB BS, Glenda M. Halliday, PhD, Jillian J. Kril, PhD, Marla Gearing, PhD, Thomas G. Beach, MD, PhD, Neill R. Graff-Radford, MBBCh, Dennis W. Dickson, MD, Rosa Rademakers, PhD, Bradley F. Boeve, MD, Stuart M. Pickering-Brown, PhD, Julie Snowden, PhD, John C. van Swieten, MD, PhD, Peter Heutink, PhD, Harro Seelaar, Jill R. Murrell, PhD, Bernardino Ghetti, MD, Salvatore Spina, MD, Jordan Grafman, PhD, Jeffrey A. Kaye, MD, Randall L. Woltjer, MD, PhD, Marsel Mesulam, MD, Eileen Bigio, MD, Albert Lladó, MD, Bruce L. Miller, MD, Ainhoa Alzualde, PhD, Fermin Moreno, MD, Jonathan D. Rohrer, MRCP, Ian R. A. Mackenzie, MD, Howard H. Feldman, MDCM, Ronald L. Hamilton, MD, Marc Cruts, PhD, Sebastiaan Engelborghs, MD, PhD, Peter P. De Deyn, MD, PhD, Christine Van Broeckhoven, PhD, DSc, Thomas D. Bird, MD, Nigel J. Cairns, PhD, Allison Goate, PhD, Matthew P. Frosch, MD, PhD, Peter F. Riederer, PhD, Nenad Bogdanovic, MD, PhD, Virginia M. Y. Lee, PhD, John Q. Trojanowski, MD, PhD, and Vivianna M. Van Deerlin, MD, PhD

Center for Neurodegenerative Disease Research, Department of Pathology and Laboratory Medicine (Drs Chen-Plotkin, Martinez-Lage, Lee, Trojanowski, and Van Deerlin, Messrs Greene and Bing, and Ms Wood), Department of Neurology (Drs Chen-Plotkin and Grossman), Center for Applied Genomics, Division of Human Genetics, Department of Pediatrics (Dr Sleiman), Department of Pathology and Laboratory Medicine (Dr Schellenberg), and Institute on Aging (Messrs Greene and Bing; Ms Wood; and Drs Lee, Trojanowski, and Van Deerlin), University of Pennsylvania School of Medicine, Philadelphia; Department of Neurology, Hospital de la Santa Creu i Sant Pau, Universitat Autonoma de Barcelona, Barcelona, Spain (Dr Martinez-Lage); Departments of Neurology (Dr Hu) and Pathology and Laboratory Medicine (Dr Gearing), Emory University School of Medicine, Atlanta, Georgia; Departments of Pathology (Drs Hatanpaa and White), Psychiatry (Dr Weiner), and Neurology (Dr Weiner), The University of Texas Southwestern Medical Center, Dallas; Neuroscience Research Australia, Sydney (Drs Brooks and Halliday); University of New South Wales, Sydney (Drs Brooks and Halliday); Disciplines of Medicine and Pathology, University of Sydney, Sydney (Dr Kril); Sun Health Research Institute, Sun City, Arizona (Dr Beach); Department of Neurology, College of Medicine, Mayo School of Graduate Medical Education (Dr Graff-Radford), and Department of Neuroscience, Mayo Clinic (Drs Dickson and Rademakers), Jacksonville, Florida; Department of Neurology, Mayo Clinic, Rochester, Minnesota (Dr Boeve); Neurodegeneration and Mental Health Research Group, University of Manchester, Manchester, England (Drs Pickering-Brown and Snowden); Department of Neurology, Erasmus Medical Centre Rotterdam, the Netherlands (Drs van Swieten and Seelaar); Section of Medical Genomics, Department of Clinical Genetics, Vrije Universiteit Medical Center, Amsterdam, the Netherlands (Dr Heutink); Department of Pathology and Laboratory Medicine and Indiana Alzheimer Disease Center, Indiana University School of Medicine, Indianapolis (Drs Murrell, Ghetti, and Spina); Department of Neurological, Neurosurgical, and Behavioral Sciences, University of Siena, Siena, Italy (Dr Spina); Traumatic Brain Injury Research Laboratory, Kessler Foundation Research Center, West Orange, New Jersey (Dr Grafman); Departments of Neurology and Biomedical Engineering (Dr Kaye) and Pathology (Dr Woltjer), Oregon Health and Science University, Portland; Cognitive Neurology, Alzheimer Disease Center, Northwestern University Feinberg School of Medicine, Chicago, Illinois (Drs Mesulam and Bigio); Alzheimer's Disease and Cognitive Disorders Unit, Service of Neurology, ICN Hospital Clínic Barcelona, Barcelona, Spain (Dr Lladó); Department of Neurology, University of California at San Francisco (Dr Miller); Ilundain Foundation, Neuroscience Unit (Dr Alzualde) and Neurology Service, Hospital Donostia (Dr Moreno), BioDonostia Institute, San Sebastian, Spain; Dementia Research Centre, UCL Institute of Neurology, London, England (Dr Rohrer); Department of Pathology, Vancouver General Hospital, University of British Columbia, Vancouver, Canada (Dr Mackenzie); Division of Neurology, University of British Columbia, Vancouver, British Columbia, Canada, and Neuroscience, Bristol-Myers Squibb, Wallingford, Connecticut (Dr Feldman); Department of Pathology, University of Pittsburgh, Pittsburgh, Pennsylvania (Dr Hamilton); Neurodegenerative Brain Diseases Group, Department of Molecular Genetics, VIB (Drs Cruts and Van Broeckhoven), Institute Born-Bunge, University of Antwerp (Drs Cruts, Engelborghs, De Deyn, and Van Broeckhoven), and Department of Neurology, Hospital Network Antwerp (ZNA) and Middelheim and Memory Clinic ZNA Hoge Beuken (Drs Engelborghs and De Deyn), Antwerpen, Belgium; Geriatric Research Education and Clinical Centers, Veterans Affairs Puget Sound Health Care System, and Department of Neurology, University of Washington, Seattle (Dr Bird); Alzheimer's Disease Research Center (Dr Cairns) and Department of Neurology (Drs Cairns and Goate), Washington University School of Medicine, St Louis, Missouri; C. S. Kubik Laboratory for Neuropathology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts (Dr Frosch); Clinic and Policlinic of Psychiatry, Psychosomatic, and Psychotherapy, University of Wuerzburg, Wuerzburg, Germany (Dr Riederer); and Geriatric Medicine and Neuropathology, Department of Geriatric Medicine, Karolinska University Hospital, Stockholm, Sweden (Dr Bogdanovic).

Correspondence: Alice S. Chen-Plotkin, MD, Department of Neurology, University of Pennsylvania, 407 Johnson Pavilion, Philadelphia, PA 19104 (Email: chenplot/at/mail.med.upenn.edu).

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Abstract

Objective

To assess the relative frequency of unique mutations and their associated characteristics in 97 individuals with mutations in progranulin (GRN), an important cause of frontotemporal lobar degeneration (FTLD).

Participants and Design

A 46-site International Frontotemporal Lobar Degeneration Collaboration was formed to collect cases of FTLD with TAR DNA-binding protein of 43-kDa (TDP-43)–positive inclusions (FTLD-TDP). We identified 97 individuals with FTLD-TDP with pathogenic GRN mutations (GRN+ FTLD-TDP), assessed their genetic and clinical characteristics, and compared them with 453 patients with FTLD-TDP in which GRN mutations were excluded (GRN− FTLD-TDP). No patients were known to be related. Neuropathologic characteristics were confirmed as FTLD-TDP in 79 of the 97 GRN+ FTLDTDP cases and all of the GRN− FTLD-TDP cases.

Results

Age at onset of FTLD was younger in patients with GRN+ FTLD-TDP vs GRN− FTLD-TDP (median, 58.0 vs 61.0 years; P<.001), as was age at death (median, 65.5 vs 69.0 years; P<.001). Concomitant motor neuron disease was much less common in GRN+ FTLDTDP vs GRN− FTLD-TDP (5.4% vs 26.3%; P<.001). Fifty different GRN mutations were observed, including 2 novel mutations: c.139delG (p.D47TfsX7) and c.378C>A (p.C126X). The 2 most common GRN mutations were c.1477C>T (p.R493X, found in 18 patients, representing 18.6% of GRN cases) and c.26C>A (p.A9D, found in 6 patients, representing 6.2% of cases). Patients with the c.1477C>T mutation shared a haplotype on chromosome 17; clinically, they resembled patients with other GRN mutations. Patients with the c.26C>A mutation appeared to have a younger age at onset of FTLD and at death and more parkinsonian features than those with other GRN mutations.

Conclusion

GRN+ FTLD-TDP differs in key features from GRN− FTLD-TDP.

FRONTOTEMPORAL LOBAR DE-generation (FTLD) is the second most common cause of dementia in individuals younger than 65 years.¹ Clinically, patients develop prominent changes in behavior, language, or both.^2-4

Frontotemporal lobar degeneration is a genetically complex disease, with some cases showing mendelian inheritance, others without a clear inheritance pattern but nonetheless demonstrating a strong hereditary component, and others that appear to be sporadic. Of the mendelian causes of FTLD, mutations in 2 genes ac count for a large proportion of the cases. In one subgroup with neuropathologic changes, characterized by tau-positive pathologic inclusions (FTLD-tau), mutations in the microtubule-associated protein tau gene, MAPT, have been shown to cause autosomal-dominant disease.^5,6 The other main neuropathologic subgroup of FTLD, characterized by TAR DNA-binding protein of 43-kDa (TDP-43)–positive inclusions (FTLD-TDP), has been associated with mutations in the progranulin gene, GRN (OMIM *138945),^7,8 as well as rarer mutations in other genes, such as TARDBP, encoding TDP-43 itself.⁹

Located on chromosome 17q21, GRN consists of 13 exons encoding a highly glycosylated 593–amino acid precursor protein with a predicted molecular mass of 63.5 kDa.^10-12 Progranulin is a widely expressed secreted protein that can be cleaved to form a family of small peptides called granulins; progranulin and the granulins may function in inflammation, wound repair, and cell cycling.^13-15

Mutations of GRN are an important cause of FTLDTDP, found in 24.7% of patients with FTLD-TDP in one series of 105 autopsy-proved cases¹⁶ and inapproximately5% of clinical FTLD cases unselected for family history.^16,17 Inherited in an autosomal-dominant manner, GRN mutations are believed to act through a haploinsufficiency mechanism,¹⁸ although recent data suggest that GRN transcript levels are elevated in brains affected by FTLD-TDP.¹⁹ To date, more than 60 GRN mutations have been reported (Alzheimer Disease & Frontotemporal Dementia Mutation Database; http://www.molgen.ua.ac.be/FTDMutations). Most mutations result in premature termination of the GRN transcript, which is lost by nonsense-mediated messenger RNA (mRNA) decay and not expressed.^7,8,16 In addition, other pathogenic mechanisms ultimately resulting in protein haploinsufficiency exist.^20-22

Frontotemporal lobar degeneration caused by GRN mutations is clinically heterogeneous, even among family members carrying the same mutation,^23-26 making genotype phenotype correlations difficult. However, certain general features of GRN-associated FTLD have been recognized. First, the neuropathologic substrate in GRN-associated FTLD appears to be FTLD-TDP.^27,28 Second, motor neuron disease (MND) appears to be rare in FTLD in GRN mutation carriers.²⁹ Third, some have proposed that GRN-associated FTLD-TDP is more likely to have parkinsonian features than FTLD-TDP without GRN mutations.³⁰

Finally, in addition to the mendelian genetic factors in FTLD, nonmendelian genetic risk factors no doubt play a role in the disease. These include the recently identified FTLD-TDP susceptibility gene TMEM106B.³¹

In the present study, we reviewed data on the largest (N=97) known collection of unrelated patients with GRN mutation–associated FTLD-TDP (GRN+ FTLD-TDP) from a 46-site international collaboration. Fifty different GRN mutations (2 novel) are represented, with the most frequent mutation (c.1477C>T, p.R493X) found in 18 unrelated individuals. Compared with 453 patients with pathologically proved FTLD-TDP but no GRN mutations (GRN− FTLD-TDP) collected from the same sites, those with GRN+ FTLD-TDP had a younger age at onset and a lower risk of concomitant MND. Our findings demonstrate that GRN+ FTLD-TDP cases differ in key aspects from GRN− FTLD-TDP cases.

METHODS

PATIENTS

Investigators from 46 clinical centers and brain banks representing 11 countries (Table 1) collaborated to collect data on patients with FTLD-TDP with clinical and demographic information under institutional review board approval as previously described.³¹ All included patients were white. The presence/absence of GRN mutations was either demonstrated by the contributing site (n=271) or determined by bidirectional sequencing at the University of Pennsylvania (n=294) as previously described.³² Patients were screened for relatedness using identity-by-state estimations (plink; http://pngu.mgh.harvard.edu/~purcell/plink/index.shtml) on 100 000 randomly distributed markers throughout the genome; pairwise pi-hat values in excess of 0.01 were considered indicators of relatedness. Demographic and clinical details were determined by the contributing site. Because of variations in clinical nomenclature, clinical diagnoses were extracted with the highest specificity possible but reclassified as 1 of 4 main diagnostic categories: behavior or language variant of frontotemporal dementia (bv/lv-FTD), Alzheimer disease (AD), dementia not otherwise specified (dementia NOS), or Parkinson disease/corticobasalsyndrome/progressivesupranuclearpalsy(PD/ CBS/PSP) for comparative purposes. See the supplementary Methods (http://www.archneurol.com).

Table 1

Countries and Institutions Contributing Cases

DNA EXTRACTION AND TDP-43 IMMUNOHISTOCHEMISTRY

DNA was extracted and evaluated for quality as previously described.³¹ All pathology cases were confirmed to have TDP-43 pathologic characteristics by immunohistochemistry as previously described.^33,34

STATISTICAL ANALYSIS

Survival curve analysis using log-rank tests was used to compare age at onset, disease duration, and age at death in GRN+ FTLD-TDP and GRN− FTLD-TDP. Two-tailed Fisher exact tests were used to compare categorical features in GRN+ FTLDTDP vs GRN− FTLD-TDP. For all tests, percentages and statistical testing were calculated based only on the cases for which relevant clinical data were available (eTable).

HAPLOTYPE ANALYSIS

Haplotypes were reconstructed and their population frequencies were estimated using the expectation-maximization algorithm implemented in the program fastPHASE.³⁵

RESULTS

GRN MUTATIONS IN THIS STUDY

An international FTLD collaboration consisting of 46 sites representing 11 countries (Table 1) was formed to collect data on FTLD-TDP cases. Five hundred fifty samples from unrelated probands were included in this study, including 453 cases of autopsy-confirmed GRN− FTLD-TDP and 97 cases of GRN+ FTLD-TDP. Among the patients with GRN mutations, 79 underwent autopsy; all were found to have TDP-43 pathologic characteristics.

Among the 97 patients with GRN+ FTLD-TDP, we found 50 different pathogenic GRN mutations (Table 2), with 16 occurring in more than 1 individual (Figure 1). The most frequent GRN mutation in our cohort was c.1477C>T (p.R493X), found in 18 patients (18.6%). The next most frequent GRN mutation was c.26C>A (p.A9D), found in 6 patients (6.2%). Two novel GRN mutations were identified in the current study: c.139delG (p.D47TfsX7) and c.378C>A (p.C126X). These patients with new mutations are described briefly.

Table 2

Pathogenic GRN Mutations in This Study^{^a}

Figure 1

Frequency of pathogenic GRN mutations. Of 50 unique pathogenic GRN mutations, 16 were found in more than 1 individual, and none of the people were related. Of these 16 mutations, 7 occurred in more than 2 individuals and constituted nearly 50% of our (more ...)

The GRN mutation c.139delG (p.D47TfsX7) was found in a woman who was diagnosed at age 72 years with “frontal lobe dementia” after 4 years of behavioral disturbances. Specifically, she was irritable, agitated, vulgar, and suspicious, with delusions of “worms crawling out of her skin.” Neurologic examination revealed stereotyped movements, rigidity, and blunted emotional responses. Family history was notable for dementing illness in her mother; no further details were available. This patient died 2 months after her diagnosis, and neuropathologic examination showed FTLD-TDP.

The GRN mutation c.378C>A (p.C126X) was found in a man who was diagnosed with Pick disease at age 57 after 4 years of progressively worsening behavioral disturbances. He died at age 63, and neuropathologic examination showed FTLD-TDP. Family history was notable for a first cousin who died 3 years before at age 62 after a 10-year history of a dementing disorder. Postmortem examination of the first cousin's brain confirmed a diagnosis of tau-negative FTLD.

COMPARISON OF FTLD-TDP WITH AND WITHOUT GRN MUTATIONS

We next compared clinical features of patients with GRN+ FTLD-TDP and GRN− FTLD-TDP. Specifically, age at onset, age at death (in autopsy cases), disease duration (in autopsy cases), sex, family history of a similar illness, and concomitant MND were compared between the 2 groups (Figure 2A).

Figure 2

Comparison of frontotemporal lobar degeneration characterized by TAR DNA-binding protein of 43-kDa–positive inclusions (FTLD-TDP) with and without GRN mutations. A, Comparing 97 patients with GRN mutations vs 453 patients with FTLD-TDP in which (more ...)

As expected, individuals with GRN mutations were more likely to have a family history, with 75.6% (59 of 78) reporting a family member with a similar illness compared with only 37.0% (122 of 330) of those with GRN− FTLD-TDP (P<.001). Moreover, age at death was lower with GRN+ FTLD-TDP vs GRN− FTLD-TDP (median age, 65.5 vs 69.0 years; P<.001) (Figure 2B), as was age at onset (median age, 58.0 vs 61.0 years; P<.001) (eFigure). Disease duration was similar in the 2 groups (median duration, 7.0 years with GRN+ FTLD-TDP vs 6.7 years with GRN− FTLD-TDP; P=.17) (Figure 2C).

Comparison of clinical presentations between FTLD-TDP with and without GRN mutations was complicated by variations in the clinical nomenclature. For comparative purposes, we collated clinical diagnoses as assigned by the contributing site and reclassified them as bv/lv-FTD, AD, dementia NOS, or PD/CBS/PSP (details in the supplementary Methods). We then determined the relative frequencies for modified clinical diagnoses for the 2 groups (Figure 2D). Diagnoses of PD, CBS, or PSP were more frequent with GRN+ FTLD-TDP vs GRN− FTLDTDP (5.3% [5 of 94] vs 1.3% [5 of 386]; P=.03). In addition to differences in clinical diagnoses, aphasic presentations were reported more frequently with GRN+ FTLD-TDP than GRN− FTLD-TDP (14.9% [14 of 94] vs 11.1% [43 of 386]; P=.37), although the difference was not statistically significant (eTable). Finally, concomitant MND was much less frequently reported in association with GRN+ FTLD-TDP vs GRN− FTLD-TDP (5.4% [5 of 93] vs 26.3% [99 of 377]; P<.001). Other clinical features and diagnoses did not differ significantly between the 2 groups. Notably, 11.3% of patients (11 of 97) with GRN+ FTLD-TDP and 18.7% of those (72 of 386) with GRN− FTLD-TDP carried clinical diagnoses of AD, suggesting that GRN mutations may occasionally be the genetic substrate for clinical AD.³⁶

Because clinical FTD-MND has rarely been reported in individuals with GRN mutation,³⁷ we further investigated the 5 patients with GRN+ FTLD-TDP and FTD-MND (Table 3). Clinical features compatible with MND were present in 4 patients, including 1 with electromyographic confirmation of denervation. In addition, 2 patients had pathologic features suggestive of upper MND, and 1 had pathologic evidence of lower MND. One GRN+ FTLD-TDP case with detailed information in support of MND is summarized in the supplementary Text.

Table 3

Clinical and Pathologic Findings Suggestive of MND Among Patients With GRN+ FTLD-TDP Designated by Contributing Site to Have MND^{^a}

CHARACTERISTICS OF C.1477C>T (P.R493X) AND C.26C>A (P.A9D)

The most common GRN mutation in our study was c.1477C>T (p.R493X), found in 18 individuals (18.6%) from 11 centers. All 18 patients shared a haplotype that spanned 630 kilobases (kb), extending from the GRN gene telomerically to the ADAM11 gene, suggesting a common founder. The extended haplotype was not present at a frequency above 0.5% in individuals without the c.1477C>T (p.R493X) mutation; however, the first 86 kb of the haplotype that extends across the linkage dis-equilibrium block adjacent to the GRN gene is relatively common and was found in 4.3% of our GRN− FTLDTDP cohort and 4.2% of the GRN+ FTLD-TDP cohort not bearing the c.1477C>T (p.R493X) mutation. We did not observe significant differences in age at onset, age at death, disease duration, presence/absence of family history, or presence/absence of MND for c.1477C>T (p.R493X), compared with other GRN mutations (Table 4). In our limited cohort, patients with the c.1477C>T (p.R493X) mutation were more likely to be male than were those with other GRN mutations.

Table 4

Clinical Features of the c.1477C>T (p.R493X) GRN Mutation Compared With Other GRN Mutations

The second most common GRN mutation in our study was c.26C>A (p.A9D), found in 6 individuals (6.2%) from 5 centers (Table 5). Age at death was younger than in patients with other GRN mutations (median, 59.0 vs 66.0 years; P=.02), as was age at onset (median, 51.0 vs 58.5 years; P=.03). Clinical diagnoses of PD, PSP, or CBS were also more frequent with c.26C>A (p.A9D) mutations compared with other GRN mutations (40.0% [2 of 5] vs 3.3% [3of91];P=.02).Thefurtherfindingthatc.26C>A(p.A9D) carriers were less likely than other GRN mutation carriers to have a family history (25.0% [1 of 4] vs 78.4% [58 of 74]; P=.04) may follow from the more heterogeneous presentations of this particular mutation. Excluding this mutation from our analyses of clinical features of GRN+ FTLD-TDP did not affect our finding that patients with GRN+ FTLD-TDP are younger at onset of the disease vs those with GRN− FTLD-TDP (median, 58.5 vs 61.0 years; P<.001) and at death (median, 66.0 vs 69.0 years; P<.001). However, c.26C>A (p.A9D) mutations may account for the more frequent parkinsonian features among GRN mutation carriers, as excluding these patients from the GRN+ FTLD-TDP group resulted in loss of the significant difference between GRN+ FTLD-TDP and GRN− FTLD-TDP in frequency of diagnoses of PD, PSP, or CBS (3.4% [3 of 89] vs 1.3% [5 of 386]; P=.17).

Table 5

Clinical Features of the c.26C>A (p.A9D) GRN Mutation Compared With Other GRN Mutations

COMMENT

In the present study, we assembled data on 97 patients with GRN mutations from a 46-site international collaboration. This is the largest collection to date of GRN mutation cases and allows estimations of relative frequencies of GRN mutations as well as comparisons between GRN+ FTLD-TDP and GRN− FTLD-TDP.

We found 50 unique GRN mutations in our 97-individual cohort. Of these, the most common was c.1477C>T (p.R493X), found in 18.6% of our GRN cases. Our result accords with previous studies showing c.1477C>T (p.R493X) to be the most common GRN mutation in one large US series¹⁶ and several smaller US series,^38,39 as well as one of the most common GRN mutations in a large UK series.⁴⁰ We did not find any meaningful phenotypic differences between the c.1477C>T (p.R493X) mutation carriers and patients with other GRN mutations, although our clinical data were limited to demographic details and diagnosis. Thus, we suspect that the preponderance of men observed in our c.1477C>T (p.R493X) carriers may be due to chance, as it has not been previously described and cannot be easily understood from a mechanistic perspective.

The second most common GRN mutation in our study was c.26C>A (p.A9D), found in 6.2% of cases, supporting prior studies that showed this mutation to be relatively common.^16,41 Interestingly, despite limitations in interpreting data from only 6 individuals with the c.26C>A (p.A9D) mutation, there appeared to be a younger age at onset, younger age at death, and higher preponderance of diagnoses within the Parkinson/Parkinson-plus spectrum for this particular GRN mutation. Indeed, unlike most other GRN mutations, c.26C>A (p.A9D) has been shown to not result in mRNA haploinsufficiency, although there may be protein haploinsufficiency because of an inability to secrete functional progranulin protein.^20,21 In light of these differences in pathogenic mechanism, it would not be surprising if carriers of this particular GRN mutation exhibited some differences in phenotype; this question could be addressed in studies with more c.26C>A (p.A9D) mutation carriers.

Accurate estimates of relative frequencies of each GRN mutation may be affected by a number of factors. First, inclusion of individuals who are closely related may over represent the frequency of a particular mutation. However, we minimized this possibility by entry criteriaand identity-by-state analysis. Second, sampling from different geographic regions/ethnic groups to different extents may affect the results. Our study included only individuals of white ancestry from Europe, North America, and Australia. Accordingly, our results may not be representative of other ethnicities and regions of the world not participating in our collaboration.

Included in our study were 2 GRN mutations that, to our knowledge, have not been described previously: c.139delG (p.D47TfsX7) and c.378C>A (p.C126X). We considered them to be pathogenic mutations because they both result in premature termination of transcript either by nonsense or frameshift mechanisms. Clinically and pathologically, neither show particularly exceptional features.

Because data on FTLD-TDP cases were collected by our collaborative group, with a special emphasis on carriers of GRN mutations, we could not assess the frequency of individual GRN mutations or GRN mutations as a whole in FTLD-TDP. However, the inclusion of 97 individuals with GRN mutations in one study allowed us to analyze in a statistically meaningful way whether there are group differences between GRN+ FTLD-TDP and GRN− FTLD-TDP. A subset of patients with GRN mutations included in this study has been reported in smaller studies from individual sites; however, the objective of the present study was to provide an overview of GRN+ FTLD-TDP, justifying our inclusion of these patients in our analyses.

We have provided clear evidence that people with FTLD-TDP who have GRN mutations are younger at the onset of the disease and at death and have a lower incidence of concomitant MND compared with FTLD-TDP patients without GRN mutations. Prior studies^16,42 have shown younger age at onset for particular mutations in particular families, but, to our knowledge, an effect across GRN mutations has not been shown. The relatively low frequency of concomitant MND in GRN+ FTLD-TDP accords with prior studies.³⁷ Although information is sparse on some patients noted to have MND, it does appear that MND is a bona fide feature of some cases of GRN+ FTLD-TDP. In addition, our data support suggestions from prior studies^6,28,37 that GRN+ FTLD-TDP may be associated with parkinsonian features more frequently than GRN− FTLD-TDP¹; this effect may be driven by the c.26C>A (p.A9D) mutations. It has been shown⁴³ that GRN+ FTLD-TDP has a global mRNA expression signature that is distinct from that of GRN− FTLD-TDP, so differences in clinical phenotype between these 2 groups are not altogether surprising.

In interpreting our data, we considered the possibility that 1 or 2 very common mutations with younger age at onset and less MND might be responsible for our findings. However, reanalysis of our data excluding either or both of the 2 most frequent mutations—c.1477C>T (p.R493X) and c.26C>A (p.A9D)—did not significantly change these results. We also considered the possibility that erroneous or missing information, always a factor in retrospective multicenter studies, or heterogeneity in ascertainment of disease and assignment of clinical diagnosis could account for our results. However, several lines of evidence make this possibility less likely. First, the omission of entire groups sharing a mutation (up to 24 GRN+ FTLD-TDP cases) did not change our main findings. Second, demographic and clinical details, along with tissue or DNA, were collected from the contributing site for the majority of patients with FTLD-TDP (294 of 550) without knowing a priori whether the individual harbored a GRN mutation; mutation status was determined by sequencing at the University of Pennsylvania. This makes it less likely that systematic reporting or ascertainment bias could create the observed differences. Indeed, we secondarily analyzed the finding that people with GRN mutations had both a younger age at onset and at death compared with those with no GRN mutations in the subgroups of patients with GRN status determined by the University of Pennsylvania vs by the contributing site and found no substantive differences in our results.

The 2006 discovery^5,8 that mutations in GRN are a cause of FTLD-TDP was a landmark research finding for a group of heterogeneous neurodegenerative dementias (ie, FTLD) that remain enigmatic diseases with respect to many key issues, including their prevalence and their underlying mechanisms of disease. In the present study, we have assembled the largest collection to date of GRN mutation cases, evaluated the relative frequencies of individual GRN mutations, and demonstrated that GRN+ FTLD-TDP differs from GRN− FTLD-TDP in key clinical features such as age at onset, age at death, and presence of MND. Studies on the specific pathways underlying these GRN- associated differences may lead to insights on pathogenesis and possibilities for therapy for an otherwise fatal disease.

Supplementary Material

Supplementary Materials

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Acknowledgments

Funding/Support: Many grant funding agencies provided financial support for this study, including the US National Institutes of Health (NIH) grants AG10129, AG10124, AG17586, AG16574, AG03949, NS44266, AG15116, NS53488, AG10124, AG010133, AG08671, NS044233, NS15655, NS065782, AG008017, AG13854, AG12300, AG028377, AG 019724, AG13846, AG025688, AG05133, AG08702, AG05146, AG005136, AG005681, AG03991, AG010129, AG05134, NS038372, AG02219, AG05138, AG10161, AG19610, AG16570, AG05142, AG005131, AG18440, AG16582, AG16573, AG033101, and the NIH Intramural Program. Additional funds were provided by Robert and Clarice Smith and Abigail Van Buren Alzheimer's Disease Research Program; the Pacific Alzheimer's Disease Research Foundation grant C06-01; the Alzheimer's Research Trust; Alzheimer's Society; Medical Research Council (Programme Grant and Returning Scientist Award); Stichting Dioraphte grant 07010500; Hersenstichting grant 15F07.2.34; Prinses Beatrix Fonds grant 006-0204; Winspear Family Center for Research on the Neuropathology of Alzheimer Disease; the McCune Foundation; Instituto Carlos III, Federal Ministry of Education and Research grant 01GI0505; SAIOTEK Program (Basque government); Department of Innovation, Diputación Foral de Gipúzkoa grant DFG 0876/08; ILUNDAIN Fundazioa, Centro de Investigaciones Biomedicas en Red en Enfermededades Neurodegenerativas; Wellcome Trust; Canadian Institutes of Health Research grant 75480; Fund for Research Foundation Flanders, the Foundation for Alzheimer Research; Medical Foundation Queen Elisabeth; Interuniversity Attraction Poles P6/43 network of the Belgian Science Policy Office; a Methusalem excellence grant of the Flemish government and Special Research Fund of the University of Antwerp; the Joseph Iseman Fund; the Louis and Rachel Rudin Foundation; National Health and Medical Research Council of Australia; Veterans Affairs Research Funds; Arizona Department of Health Services contract 211002, Arizona Alzheimer's Research Center; the Arizona Biomedical Research Commission contracts 4001, 0011, and 05-901 to the Arizona Parkinson's Disease Consortium; the Prescott Family Initiative of the Michael J. Fox Foundation for Parkinson's Research; the Daljits and Elaine Sarkara Chair in Diagnostic Medi cine; BrainNet Europe II; Ministerio de Ciencia y Tecnología; Ref Saud y Farmacia 2001-4888; and Fundacion La Caxia.

Additional supported was provided by the Burroughs Wellcome Fund Career Award for Medical Scientists and the Benaroya Fund (Dr Chen-Plotkin). Dr Lee is the John H. Ware III Professor of Alzheimer's Disease Research, and Dr Trojanowski is the William Maul Measey-Truman G. Schnabel Jr Professor of Geriatric Medicine and Gerontology.

Footnotes

Author Contributions: Study concept and design: Chen-Plotkin, Martinez-Lage, Lee, Trojanowski, and Van Deer-lin. Acquisition of data: Chen-Plotkin, Martinez-Lage, Sleiman, Hu, Greene, Wood, Bing, Grossman, Schellenberg, Hatanpaa, Weiner, White, Brooks, Halliday, Kril, Gearing, Beach, Graff-Radford, Dickson, Rademakers, Boeve, Pickering-Brown, Snowden, van Swieten, Heutink, Seelaar, Murrell, Ghetti, Spina, Grafman, Kaye, Woltjer, Mesulam, Bigio, Lladó, Miller, Alzualde, Moreno, Rohrer, Feldman, Hamilton, Cruts, Engelborghs, De Deyn, Van Broeckhoven, Bird, Cairns, Goate, Frosch, Riederer, Bogdanovic, Lee, Trojanowski, and Van Deerlin. Analysis and interpretation of data: Chen-Plotkin, Martinez-Lage, Sleiman, Hu, Murrell, Ghetti, Mackenzie, Hamilton, De Deyn, Lee, Trojanowski, and Van Deerlin. Drafting of the manuscript: Chen-Plotkin, Bing, White, Hamilton, Trojanowski, and Van Deerlin. Critical revision of the manuscript for important intellectual content: Chen-Plotkin, Martinez-Lage, Sleiman, Hu, Greene, Wood, Grossman, Schellenberg, Hatanpaa, Weiner, Brooks, Halliday, Kril, Gearing, Beach, Graff-Radford, Dickson, Rademakers, Boeve, Pickering-Brown, Snowden, van Swieten, Heutink, Seelaar, Murrell, Ghetti, Spina, Grafman, Kaye, Woltjer, Mesulam, Bigio, Lladó, Miller, Alzualde, Moreno, Rohrer, Mackenzie, Feldman, Cruts, Engelborghs, De Deyn, Van Broeckhoven, Bird, Cairns, Goate, Frosch, Riederer, Bogdanovic, Lee, Trojanowski, and Van Deerlin. Statistical analysis: Chen-Plotkin. Obtained funding: White, Beach, Rademakers, Pickering-Brown, Ghetti, Spina, Cruts, Van Broeckhoven, Goate, and Trojanowski. Administrative, technical, and material support: Chen-Plotkin, Martinez-Lage, Wood, Grossman, Schellenberg, Hatanpaa, White, Halliday, Kril, Gearing, Beach, Dickson, Rademakers, Boeve, Snowden, Murrell, Ghetti, Grafman, Kaye, Woltjer, Alzualde, Moreno, Mackenzie, Hamilton, Cruts, Van Broeckhoven, Cairns, Frosch, Riederer, Lee, Trojanowski, and Van Deerlin. Study supervision: Chen-Plotkin, Pickering-Brown, Van Broeckhoven, Goate, Lee, Trojanowski, and Van Deerlin.

Financial Disclosure: None reported.

Online-Only Materials: The eTable, eFigure, and supplementary Methods and text are available at http://www.archneurol.com.

Additional Contributions: This project was enabled by the contributions and efforts of many individuals in several supportive capacities. Most important, we extend our appreciation to the patients and families who made this research possible. Technical assistance was provided by T. Unger and C. Kim. The following individuals contributed through sample ascertainment, epidemiology, coordination, and/or clinical evaluation of cases: S. E. Arnold, D. M. A. Mann, H. Seelaar, J. Hodges, M. G. Spillantini, S. Gilman, A. P. Lieberman, S. al-Sarraj, C. Troakes, R. N. Rosenberg, I. Ferrer, M. Neumann, H. A. Kretzschmar, C. M. Hulette, K. A. Welsh-Bohmer, A. Lopez de Munain, A. C. McKee, A. I. Levey, J. J. Lah, J. Hardy, M. Rossor, T. Lashley, S. T. DeKosky, J. van der Zee, PhD, S. Kumar-Singh, MD, PhD, R. Mayeux, J.-P. Vonsattel, J. C. Troncoso, J. B. J. Kwok, P. G. Ince, P. J. Shaw, J. C. Morris, C. A. McLean, C. DeCarli, W. G. Ellis, S. M. Freeman, J. H. Growdon, D. P. Perl, M. Sano, D. A. Bennett, J. A. Schneider, E. M. Reiman, B. K. Wood-ruff, J. Cummings, H. V. Vinters, C. A. Miller, H. C. Chui, W. Mack, I. Alafuzoff, P. Hartikainen, D. Seilhean, D. Galasko, E. Masliah, C. W. Cotman, M. T. Tuñón, M. C. Caballero-Martínez, D. G. Munoz, S. L. Carroll, D. Marson, and all others who participated in the International Frontotemporal Lobar Degeneration Collaboration. We also thank the Brain Bank of the University of Barcelona, Hospital Clinic; Brain Bank of Navarra (Spain); Brain Bank of the Institute of Neuropathology, Hospital Universitari de Bellvitge; Clinic for Alzheimer's Disease and Related Disorders, University of British Columbia; Australian Brain Donor Programs supported by the National Health and Medical Research Council of Australia; Biobank at the Institute Born-Bunge, University of Antwerp, Antwerpen, Belgium; and the French clinical and genetic research network on FTD/FTD-MND.

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