Design  Antemortem and postmortem characterization of a kindred with a familial neurodegenerative disorder.

Setting  Multispecialty group academic medical center.

Patients  Affected members of a kindred with dementia with or without parkinsonism associated with a unique mutation in PGRN.

Main Outcome Measure  Genotype-phenotype correlation.

Results  Of 10 affected individuals identified, 6 presented with early amnestic symptoms which resulted in initial diagnoses of Alzheimer disease or amnestic mild cognitive impairment. Some individuals presented with features characteristic of frontotemporal dementia. Mean age at onset was substantially younger in generation III (75.8 years; range, 69-80 years) than in generation II (60.7 years; range, 55-66 years). The pattern of cerebral atrophy varied widely in the affected individuals. Neuropathologic features in 6 individuals included frontotemporal lobar degeneration with ubiquitin-positive neuronal cytoplasmic and intranuclear inclusions (FTLD-U with NII). PGRN analysis revealed a single base pair deletion in exon 2 (c.154delA), which caused a frameshift (p.Thr52HisfsX2) and, therefore, creation of a premature termination codon and a likely null allele.

Conclusions  In this large kindred, most affected individuals had clinical presentations that resembled Alzheimer disease or amnestic mild cognitive impairment associated with a mutation in PGRN and underlying FTLD-U with NII neuropathologic abnormalities. This finding is in distinct contrast to previously reported kindreds, in which clinical presentations have typically been within the spectrum of FTLD. The basis for the large difference in age at onset between generations requires further study.

METHODS

Seven members of this kindred were evaluated at Mayo Clinic, Rochester, Minnesota, and the same mutation in PGRN was identified in all 7 individuals. The proband and 5 other members were enrolled in the Mayo Clinic Alzheimer’s Disease Research Program, in a Mayo Foundation institutional review board–approved program. Genetic analyses, MRI scans, and eventual autopsies were performed after participants or appropriate proxies provided written informed consent.

EVALUATIONS

All neurobehavioral clinical data⁶ were reviewed and summarized. Age at onset was determined to be the age at which the patient first demonstrated behavioral or personality change, memory loss, or other cognitive or motor changes as noted by themselves, family, friends, or colleagues.

Blood samples were obtained from those living family members who provided informed consent. DNA was extracted from peripheral blood leukocytes, and sequence analysis of apolipoprotein E, microtubule-associated protein tau (MAPT), and PGRN from patient genomic DNA was performed as previously described.^{1, 7}

We performed MRI using a 1.5-T scanner (General Electric Medical Systems, Milwaukee, Wisconsin); images of the brain were obtained in 3 planes: sagittal (T1-weighted), axial (proton-density, T2-weighted, and fluid-attenuated inversion recovery [FLAIR], and coronal (T1-weighted or FLAIR).

Sections of neocortex, hippocampus, thalamus, basal ganglia, midbrain, pons, medulla, and cerebellum were stained with hematoxylin-eosin and thioflavin S fluorescent microscopy, and immunocytochemical analysis was performed for phospho-tau. Sections of cortex and hippocampus were also stained with Bielschowsky and Luxol fast blue and were immunostained for ubiquitin, neurofilament, Aβ40, and Aβ42. Midbrain and amygdala sections were studied using -synuclein immunostains. In selected cases, we applied immunohistochemical analysis for TDP-43 (1:8000) (Proteintech Group Inc, Chicago, Illinois).

Neuropathologic diagnoses were based on established guidelines.⁸ Diagnosis of FTLD-U was made if there was neuronal loss and gliosis that affected the frontal or temporal lobe plus ubiquitin-positive and tau-negative, -synuclein–negative, and neurofilament-negative intraneuronal inclusions or neurites in frontal or temporal neocortex or hippocampal dentate granule cells, in the absence of any evidence of motor neuron degeneration.⁹ For the patient who had multiple pathologic abnormalities, including FTLD-U, TDP-43 immunohistochemical staining was used to confirm the diagnosis of FTLD-U.

RESULTS

Figure 1 shows the pedigree of this kindred. Table 1 provides a summary of the clinical, radiologic, and neuropathologic findings of all affected individuals.

View larger version (14K): [in this window] [in a new window] [as a PowerPoint slide]   Figure 1. Pedigree. Arrows pointing to the right in a sibship represent additional unaffected persons, who were purposefully excluded to maintain confidentiality.

View this table: [in this window] [in a new window] [as a PowerPoint slide]   Table 1. Demographic, Clinical, Radiologic, and Neuropathologic Findings in Affected Individuals

At age 69 years, the proband (patient II:5) began experiencing forgetfulness and decreased verbal comprehension that did not impair daily activities. This patient reported difficulty making plans and remembering appointments and names. No personality changes were noted by this patient or others. Performance on the Short Test of Mental Status (STMS)¹⁰ was 32 of 38 (normal, >29), notable for impaired recall (0 of 4 items). Neuropsychological testing confirmed this memory impairment, with preserved function in other cognitive spheres. The patient scored 125 of 144 (mildly impaired) on the Dementia Rating Scale (DRS)¹¹ and recalled 0 items on delayed recall of the Rey Auditory Verbal Learning Test.¹² No obvious abnormalities were present on MRI scans of the brain. The patient was diagnosed as having amnestic mild cognitive impairment.¹³ Cognition remained stable at follow-up 1 year later.

At age 71 years, the patient developed paranoid thoughts and delusions of spousal infidelity, on rare occasions mistaking the spouse for someone else. Performance on the STMS was minimally changed (30 of 38 total and 1 of 4 recall), and the DRS score was 127 of 144. During the subsequent year, neurobehavioral features began to limit the functional status of the patient in the home environment. By age 72 years, day-to-day memory problems had worsened, and difficulties in other areas of cognition had emerged. Judgment was impaired in even simple household matters, and thought processes had become disorganized. The patient required constant supervision by family, and the spouse of the patient found it necessary to place additional locks on the doors to prevent nocturnal wandering. The STMS had declined to 28 of 38, and the patient exhibited difficulties with procedural skills and mild disorientation regarding time. The DRS score declined to 108 (moderately impaired). The clinical diagnosis was changed to clinically probable AD.

This patient rapidly deteriorated, developing profound depression that was refractory to medication and electroconvulsive therapy. By age 74 years, the patient had become incontinent owing to standing up immediately after voiding of the bladder; this condition improved dramatically when the patient was given an Etch A Sketch (Ohio Art Co, Bryan, Ohio) or playing cards to occupy time during voiding. On examination, mild rigidity in all extremities, stooped posture, and small steps on gait testing were noted. The mental status of the patient was untestable. The MRI scans at this time showed mild atrophy along the anterior falx, more obvious atrophy in both hippocampi, and mild leukoaraiosis (Figure 2). The final diagnosis remained probable AD. The patient died at age 76 years, and neuropathologic examination demonstrated FTLD-U with neuronal intranuclear inclusions (NII).

View larger version (97K): [in this window] [in a new window] [as a PowerPoint slide]   Figure 2. Representative coronal T1-weighted or fluid-attenuated inversion recovery (FLAIR) images and axial FLAIR images for each affected individual for whom magnetic resonance imaging scans were available. Patients II:4 and III:2 show frontotemporal atrophy, with subcortical white matter FLAIR hyperintensity present in the regions of maximal atrophy in patient II:4. Patient II:5 shows mild generalized atrophy and hippocampal atrophy. Patient III:1 shows atrophy along the anterior falx but no significant hippocampal atrophy. For patient III:3, serial imaging was available that documented progressive left hemispheric atrophy, maximal in the temporal lobe. AD indicates Alzheimer disease; aMCI, amnestic mild cognitive impairment; FTD, frontotemporal dementia; FTDP, FTD and parkinsonism; md-MCI + a, multidomain MCI with amnesia; and PPA, primary progressive aphasia.

One of the parents of the patient (patient I:1) had developed memory impairment and then dementia at approximately age 69 years, was diagnosed as having AD, and had died at age 74 years. The other parent (patient I:2) had experienced 3 years of cognitive decline after a hip fracture and had died at age 86 years. The proband had 4 siblings who developed dementia.

Patient II:1 died of presumed AD at age 86 years. The family of this patient estimated the age at onset to be approximately 79 years, with early memory impairment, and the patient was no longer making personal medical decisions by age 81 years. Initial neuropathologic examination showed changes typical of mixed AD (Braak stage V, National Institute on Aging–Reagan score high likelihood) and vascular dementia. Reexamination of tissue via ubiquitin and TDP-43 immunocytochemical staining showed coexisting FTLD-U with NII.

Patient III:1, the child of the above-mentioned sibling, presented with memory concerns at age 66 years. This patient reported insidious onset of difficulties in the recall of upcoming appointments and details of recent events but remained independent in all simple and complex activities of daily living. Clinical examination found poor recall on the STMS, with a total score of 29 of 38. Results of neuropsychological testing confirmed impairments in memory, naming, and attention/organization. The patient scored 122 (mild impairment) on the DRS. An MRI scan demonstrated mild diffuse atrophy, more obvious along the anterior falx; no significant mesial temporal atrophy was present (Figure 2). The patient was diagnosed as having multiple-domain mild cognitive impairment with amnesia.¹³

Patient II:2 developed dementia and apathy and died at age 82 years. It is unclear whether this patient had parkinsonian features. The child of that patient (patient III:2) experienced progressive apathy and difficulties with the performance of activities around the home beginning at age 55 years. Initially, memory was unaffected, although later it declined. The physicians who attended this patient had given a diagnosis of AD before the arrival at Mayo Clinic. The patient exhibited features of Kluver-Bucy syndrome, with consequent weight gain at age 58 years. Visual hallucinations, misidentification, and parkinsonism developed at approximately age 60 years, and dementia with Lewy bodies was suspected. Examination at Mayo Clinic found global cognitive impairment associated with abulia and left hemiparkinsonism. An MRI scan identified moderately severe generalized cerebral atrophy, most pronounced in the right temporal lobe (Figure 2). The patient was diagnosed with FTDP and died 3 years later at age 65; the neuropathologic examination demonstrated FTLD-U with NII.

Patient II:3 developed memory difficulties at age 75 years. This patient had minimal knowledge of recent events, had stopped driving, and was diagnosed as having probable AD. At age 76 years, the patient experienced rigidity and resting tremor that did not improve with carbidopa-levodopa therapy. The patient died at age 77 years of pneumonia. Neuropathologic examination demonstrated FTLD-U with NII.

The child of that patient (patient III:3) developed impaired verbal comprehension at age 61 years. Anomia and expressive language difficulties followed. No personality changes were noted, and this patient remained independent in complex activities of daily living. Neuropsychological testing demonstrated expressive and receptive aphasia with sparing of other cognitive domains. Comprehension was better for written language than for spoken language. An MRI scan demonstrated moderate atrophy of the left anterior inferolateral temporal lobe and mild atrophy of the left frontal opercular region (Figure 2). A single-photon emission computed tomograph showed mild decreased uptake in the entire left hemisphere and severe decreased uptake in the left temporal region. This patient was diagnosed as having primary progressive aphasia. Language impairments progressed, with comprehension clearly impaired but much less so than expressive function.

By age 64 years, this patient had developed acalculia, and there were the beginnings of a decline of nonverbal abilities. Despite having no meaningful verbal output by age 65 years, the patient continued to function independently, using a credit card to make grocery purchases because of the current inability to write checks. Behavioral disturbances typical of frontotemporal dementia (FTD) became evident the following year, and the patient became progressively more anxious and combative. Follow-up MRI scans documented progressive atrophy, more prominently involving the left hemisphere and most severely involving the left temporal lobe (Figure 2). The patient was diagnosed with mixed primary progressive aphasia and FTD. This person died at age 70, and the neuropathologic examination demonstrated FTLD-U with NII.

Patient II:4 first developed cognitive and behavioral changes at age 80 years. Substantial decline in memory, language skills, and attention and executive function was evident by age 83 years, when these problems first came to medical attention. This patient had limited knowledge of recent events, and the family noted dents in the car of the patient that the patient was unable to explain. The patient had lost 6.3 kg and provided only vague descriptions of meals claimed to have been prepared for personal consumption. During examination, the patient was inattentive and disoriented, having difficulties with memory, naming, and executive function. Neuropsychological testing confirmed these deficits, and the DRS score was 84 (moderately severe impairment). Performance on the Rey Auditory Verbal Learning Test and other memory tests documented significant impairment in delayed recall. The primary care physician diagnosed probable AD. Behaviors that were out of character for the established personality subsequently developed, such as telling a relative, "You're too fat." By age 84 years, the responses of the patient consisted of one word followed by laughter; there were no meaningful verbalizations produced and no commands followed by the time the patient reached the age of 85 years. Bilateral upper-extremity rigidity and left leg resting tremor were noted on examination. An MRI scan at age 85 years demonstrated prominent atrophy, more pronounced in the frontal and temporal lobes, and patchy bilateral frontal white matter T2 hyperintensity with extension into the high-convexity cortex. Periventricular white matter signal changes were also noted (Figure 2). The patient had no significant vascular risk factors; hence, the diagnosis was changed to FTD. The patient died at age 87 years, and neuropathologic examination found FTLD-U with NII and remarkably no AD pathologic abnormalities.

Analysis of PGRN in 7 affected members of this kindred revealed a single base pair deletion in exon 2 (c.154delA). This frameshift mutation (p.Thr52HisfsX2) creates a premature termination codon, which likely resulted in a null allele through nonsense-mediated decay.¹

GROUP CONSIDERATIONS

Table 2 summarizes the demographic and clinical information regarding this kindred, grouped by generation. The mean age at onset is substantially earlier in the third generation (GIII) compared with the second generation (GII). Disease duration is similar, although all members of GIII are still living. Generation II exhibited less phenotypic heterogeneity.

View this table: [in this window] [in a new window] [as a PowerPoint slide]   Table 2. Summary of Demographics and Clinical Data Grouped by Generation

Data from MRI were available in 5 patients, with representative images presented in Figure 2. The topography of cortical atrophy was highly variable, with no apparent cerebral hemisphere predominance. Striking subcortical white matter signal changes with a frontal predominance were present in patient II:4 and were less prominent in the right temporal lobe in patient III:2. These subcortical signal changes were most prominent in the cortical regions, where atrophy was maximal, and the extent of signal change became more evident with greater symptomatic disease duration. Longitudinal MRI scans that covered 2 or more years were available in 3 patients, which all showed progression of atrophy and subcortical white matter signal changes similar to those that have been described in another FTDP case with a PGRN mutation.³

COMMENT

Prominent early memory impairment is characteristic of amnestic mild cognitive impairment and AD and is an exclusionary criterion for the diagnosis of FTD.¹⁴ Generally, the neurofibrillary tangles in the mesial temporal lobes characteristic of AD form the pathologic substrate for this type of prominent memory impairment. In this family, 3 individuals who had a clinical presentation and subsequent clinical course typical of AD were found to have FTLD-U with NII as the pathologic substrate. This clinical phenotype is distinct from that seen in other described kindreds that have mutations in PGRN associated with FTLD-U with NII neuropathologic features⁵ and is atypical in association with familial FTLD neuropathologic features in general.

These data confirm the phenotypic heterogeneity observed in other kindreds. Several members had primarily amnestic difficulties, 1 member followed an early course typical of primary progressive aphasia, another followed the typical course of FTDP, and 1 initially had amnestic symptoms that evolved into a clinical picture of FTD within 1 year. Similar heterogeneity has been reported within families and among families with identical mutations in microtubule-associated protein tau.¹⁵

Parkinsonism has been a predominant phenotype in other kindreds,¹⁶ but it was not a dominant clinical finding in this kindred. When present, parkinsonism developed late in the clinical course and was generally appreciated on examination (rather than tremor, falls, and bradykinesia being noted by family members). Whether parkinsonism is more predominant among certain PGRN mutations remains to be seen, similar to parkinsonism being the predominant phenotype in the N279K mutation in microtubule-associated protein tau.¹⁷

The mean age at onset in GII was 75.8 years, whereas that in GIII was 60.7 years, which suggests an earlier onset in GIII. Plus, several patients in both generations were evaluated early in their course (and in 2 patients presymptomatically) by a behavioral neurologist. One could argue that heightened suspicion of a familial disorder would lead GIII patients to possibly seek medical attention earlier in their course than those in GII, but we find it difficult to explain a 15-year difference in the mean age at onset based purely on this possibility. The fact that behavioral neurologists evaluated individuals early in the course in both generations also argues against this hypothesis. Individuals in GII and GIII carry the same PGRN mutation, a finding that possibly implies that other genetic or environmental factors may account for the observed difference in age at onset.

In some families with PGRN mutations, the same cerebral hemisphere was maximally affected.^18-19 The reasons for this result remain unclear. In this kindred, no hemispheric predilection was present, with widely variable patterns of atrophy.

The MRI abnormalities typically reported in sporadic and familial FTD have been frontotemporal cortical abnormalities that vary from symmetrical to markedly asymmetrical atrophy.^20-22 Most descriptions have not reported subcortical white matter signal changes. One individual in this kindred had striking subcortical white matter signal changes adjacent to the regions of maximal cortical atrophy, and in 1 other patient, a milder degree of subcortical signal changes was present. Data from MRI have been reported in few cases of PGRN mutations, and it is not yet possible to determine whether these signal changes are sensitive or specific for detecting PGRN mutation–positive FTLD. Volumetric analysis of a few individuals that have FTLD-U with neuropathologic features suggested more severe and widespread frontal, temporal, and parietal atrophy in those having PGRN mutations.²³

Brain tissue was examined in 4 patients, all of which demonstrated features of FTLD-U with NII. As has been previously reported, the presence of NII is a feature of FTLD-U with PGRN mutations, although it is not specific for this diagnosis.^24-25

Patient II:1 had mixed FTLD-U with NII, with vascular and AD pathologic abnormalities. A recent study suggested that immunohistochemical staining for ubiquitin or TDP-43 may be a useful adjunct to identify FTLD-U pathologic abnormalities in the presence of additional pathologic processes,^{24, 26} and this technique was used to confirm the presence of FTLD-U pathologic abnormalities in patient II:1. As in previously reported kindreds, the pattern of inheritance was autosomal dominant. Penetrance is high, although not 100%,⁴ with at least 1 asymptomatic carrier identified.

The presence of prominent early anterograde amnesia in this family with a mutation in PGRN and pathologic FTLD demonstrates the limitations of clinicopathologic correlations and diagnostic criteria in neurodegenerative disease. Anterograde amnesia is the prototypical manifestation of AD, and the preservation of new learning is one of the diagnostic criteria for the FTLD syndromes. At least in this unusual family, purely clinical diagnostic criteria failed to properly identify the pathologic substrate of their illness. In contrast, most of the MRI scans in these patients showed a variety of features that were distinctly of a non-AD type. Clinical diagnostic criteria could be enhanced by adding explicit inclusion and exclusion imaging features for AD and the FTLD syndromes.

AUTHOR INFORMATION

Accepted for Publication: June 9, 2007.

Author Contributions: All authors had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Kelley, Boeve, and Parisi. Acquisition of data: Kelley, Haidar, Boeve Baker, Shiung, Knopman, Rademakers, Hutton, Adamson, Dickson, and Parisi. Analysis and interpretation of data: Kelley, Boeve, Baker, Kuntz, Parisi, Smith, and Petersen. Drafting of the manuscript: Kelley, Haidar, Boeve, Shiung, and Kuntz. Critical revision of the manuscript for important intellectual content: Kelley, Boeve, Baker, Knopman, Rademakers, Hutton, Adamson, Dickson, Parisi, Smith, and Petersen. Obtained funding: Hutton and Petersen. Administrative, technical, and material support: Haidar, Boeve, Baker, Shiung, Rademakers, Hutton, Adamson, Kuntz, and Smith. Study supervision: Boeve, Knopman, and Parisi.

Financial Disclosure: None reported.

Funding/Support: This research was supported by grants AG06786, AG16574, AG11378, and AG07216 from the National Institute on Aging and by the Robert H. and Clarice Smith and Abigail Van Buren Alzheimer's Disease Research Program of the Mayo Foundation. Dr Rademakers was a postdoctoral fellow from the Fund for Scientific Research Flanders at the time of this study.

Additional Contributions: We thank our research staff for their assistance in evaluating these patients. We particularly thank the members of this family for participating in neurodegenerative disease research.