Alzheimer's Disease-Like Phenotype Associated With the c.154delA Mutation in Progranulin

Abstract

Objective

To characterize a kindred with a familial neurodegenerative disorder associated with a mutation in progranulin (PGRN), emphasizing the unique clinical features in this kindred.

Design

Clinical, radiologic, pathologic, and genetic characterization of a kindred with a familial neurodegenerative disorder.

Setting

Multispecialty group academic medical center.

Patients

Affected members of a kindred with dementia +/- parkinsonism associated with a unique mutation in PGRN.

Main Outcome Measure

Genotype-phenotype correlation.

Results

Ten affected individuals were identified, among whom six presented with initial amnestic complaints resulting in initial diagnoses of AD or amnestic mild cognitive impairment (MCI). A minority of individuals presented with features characteristic of FTD. The ages of onset of generation II (mean 75.8 years, range 69-80 years) were far greater than those of generation III (mean 60.7 years, range 55-66 years). The pattern of cerebral atrophy varied widely among affected individuals. Neuropathology in six individuals showed frontotemporal lobar degeneration with ubiquitin positive neuronal cytoplasmic and intranuclear inclusions (FTLD-U + NII). PGRN analysis revealed a single base pair deletion in exon 2 (c.154delA), causing a frameshift (p.Thr52Hisfs×2) and therefore creation of a premature termination codon and likely null allele.

Conclusions

We describe a large kindred in which the majority of affected individuals had clinical presentations resembling AD or amnestic MCI in association with a mutation in PGRN and underlying FTLD-U + NII neuropathology. This is in distinct contrast to previously reported kindreds, where clinical presentations have typically been within the spectrum of FTLD. The basis for the large difference in age of onset between generations will require further study.

Introduction

Alzheimer's disease is pathologically characterized by neurofibrillary tangles and neuritic plaques. The hallmark of the cognitive profile is prominent early memory disturbance, in distinct contrast to the frontotemporal lobar degenerations (FTLD), in which pathological FTLD is usually associated with prominent early executive, behavioral and/or language disturbances typical of frontotemporal dementia with or without parkinsonism (FTDP). We recently reported several kindreds of FTDP associated with frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U) pathology in association with mutations in the gene encoding progranulin (PGRN).^1-4 Subsequently published clinical phenotypes have included FTDP, primary progressive aphasia (PPA), corticobasal syndrome (CBS), and progressive supranuclear palsy (PSP).⁵ This paper presents a detailed description of a large kindred in which several individuals have followed a clinical course typical of Alzheimer's disease, in association with a mutation in PGRN and underlying FTLD-U pathology. These findings extend the clinical phenotypes and MRI findings associated with mutations in PGRN with the pathological substrate of FTLD-U.

Methods

Subjects

Seven members of this kindred were evaluated at Mayo Clinic Rochester and the same mutation in PGRN was identified all seven individuals. The proband and five other members were enrolled in the Mayo Clinic Alzheimer Disease Research Center, a Mayo Foundation Institutional Review Board-approved program. Genetic analyses, MRI scans, and eventual autopsies were performed after the subjects or appropriate proxies provided written consent.

Clinical Evaluations

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

Laboratory Analyses

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

Neuroimaging Examinations

MRI was performed using a GE scanner at 1.5 Tesla, and images of the brain were obtained in the sagittal (T1-weighted), axial [proton-density, T2-weighted, and fluid attenuation inversion recovery (FLAIR)], and coronal (T1-weighted or FLAIR) planes.

Neuropathologic Examination

Sections of neocortex, hippocampus, thalamus, basal ganglia, midbrain, pons, medulla and cerebellum were stained with hematoxylin and eosin and thioflavin-S fluorescent microscopy, as well as immunocytochemistry for phospho-tau. Sections of cortex and hippocampus were also stained with Bielschowsky and Luxol fast blue, and immunostained for ubiquitin, neurofilament, Aβ40, and Aβ42. Midbrain and amygdale sections were studied with alpha-synuclein immunostains. In selected cases we applied immunohistochemistry for TDP-43 (1:8000; Proteintech Group, Chicago, IL).

Neuropathological diagnoses were based on established guidelines.⁸ Diagnosis of frontotemporal lobar degeneration with ubiquitin-only immunoreactive neuronal changes (FTLD-U) was made if there was neuronal loss and gliosis affecting frontal or temporal lobe, plus ubiquitin positive, tau, alpha-synuclein 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 In the case having multiple pathologies including FTLD-U, application of TDP-43 immunohistochemistry was used to confirm the diagnosis of FTLD-U.

Results

Clinical descriptions

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

Figure 1.

Pedigree. Circles represent females, squares represent males, shaded shapes represent affected individuals. Diagonal lines indicate deceased individuals. A shaded arrowhead indicates the proband. An arrow pointing to the right in a sibship represents additional unaffected persons, purposefully excluded to maintain confidentiality.

Table 1.

Demographic, clinical, radiologic, and neuropathologic findings of affected individuals

Case	I.1	I.2	II.1	II.2	II.3	II.4	II.5 (p)	III.1	III.2	III.3
Age at Onset	69	83	79	*	75	80	69	66	55	61
Age at Death	74	86	86	82	77	87	76	Alive 71	65	70
Duration	5	3	7	*	2	7	7	> 5	10	9
Initial Diagnosis	AD	Dem NOS	AD	Dem NOS	AD	AD	aMCI	md-MCI + a	FTD + DLB	PPA
Final Diagnosis	AD	Dem NOS	AD	Dem NOS	AD + park	FTD	AD	md-MCI + a	FTDP	PPA + FTD
Memory Impairment	present	*	early	present	early	early	early	early	mid	late
Personality Change	*	*	*	present	present	early	late	*	early	late
Executive Dysfunction	*	*	*	*	present	mid	late	early	early	late
Language Dysfunction	*	*	*	*	*	mid	late	early	present	early
Parkinsonism	*	*	*	*	mid	late	late/term	absent	late	absent
MRI Topography of Atrophy						L>R F,T	mild L>R T	mild gen, falcine	mod gen, sev R T	L T>F
Pathology			FTLD-U + NII + AD + VD		FTLD-U + NII	FTLD-U + NII	FTLD-U + NII		FTLD-U + NII	FTLD-U + NII

Abbreviations: AD=Alzheimer's disease; aMCI=amnestic mild cognitive impairment;B=bilateral; Dem NOS=dementia not otherwise specified; DLB=dementia with Lewy bodies; F=frontal; FTD=frontotemporal dementia; FTDP=frontotemporal dementia and parkinsonism; FTLD-U + NII=frontotemporal lobar degeneration with ubiquitin positive neuronal cytoplasmic and intranuclear inclusions; gen=generalized; L=left; md-MCI + a=multi-domain mild cognitive impairment with amnesia; mod=moderate; (P)=proband; park=parkinsonism; PPA=primary progressive aphasia; R=right; T=temporal; VD=vascular dementia. early=onset within first year of symptoms; mid=onset 1-2 years after symptom onset; late=onset 3 or more years after onset; absent=no evidence in clinical records of this feature being present. Asterisks represent unavailable information

At age 69 the proband (Case II.5) began experiencing forgetfulness and decreased verbal comprehension that did not impair daily activities. The patient reported difficulty making plans and remembering appointments and names. No personality changes were noted by the patient or others. Performance on the Short Test of Mental Status¹⁰ (STMS) was 32/38 (normal >29), notable for impaired recall (0/4 items). Neuropsychologic testing confirmed this memory impairment, with preserved function in other cognitive spheres. The patient scored 125/144 (mildly impaired) on the Dementia Rating Scale (DRS)¹¹ and recalled 0 items on delayed recall of the Rey Auditory Verbal Learning Test (AVLT).¹² No obvious abnormalities were present on MRI of the brain. The patient was diagnosed with amnestic mild cognitive impairment (a-MCI).¹³ Cognition remained stable at follow-up one year later.

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

t\The patient rapidly deteriorated, developing profound depression refractory to both medication and electroconvulsive therapy. By age 74 the patient had become incontinent due to standing up immediately after sitting to void; this improved dramatically when the patient was given an Etch-a-Sketch or cards to occupy time during voiding. On examination, mild rigidity in all extremities, stooped posture and small steps on gait testing were noted. Mental status was untestable. MRI at this time showed mild atrophy along the falx anteriorly, more obvious atrophy in both hippocampi, as well as mild leukoaraiosis (Figure 2). The patient's final diagnosis remained probable AD. The patient died at age 76, and neuropathological examination demonstrated FTLD-U with NII.

Figure 2.

Representative coronal T1-weighted or fluid attenuation inversion recovery (FLAIR) images, and axial FLAIR images, for each affected individual for which MRI scans were available, labeled by case number and phenotype. Cases II.4 and III.2 show frontotemporal atrophy, with subcortical white matter FLAIR hyperintensity present in the regions of maximal atrophy in case II.4. Case II.5 shows mild generalized atrophy and hippocampal atrophy. Case III.1 shows atrophy along the falx anteriorly, but no significant hippocampal atrophy. Serial imaging was available in case III.3, documenting progressive left hemispheric atrophy, maximal in the temporal lobe.

A parent of the patient (Case I.1) developed memory impairment and then dementia around age 69, was diagnosed with AD and died at age 74. The other parent (Case I.2) experienced 3 years of cognitive decline following a hip fracture and died at age 86. The proband had four siblings who developed dementia.

Case II.1 died of presumed AD at age 86. The patient's family estimated the age of onset around age 79 with early memory impairment, and the patient was no longer making medical decisions by age 81. Initial neuropathological examination showed changes typical of mixed Alzheimer's disease (Braak V, NIA-Reagan high likelihood) and vascular dementia. Re-examination of tissue with ubiquitin and TDP-43 immunocytochemistry showed coexisting FTLD-U plus NII.

This patient's child (Case III.1) presented with memory complaints at age 67. This patient reported insidious onset of difficulties recalling 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 29/38. Neuropsychological testing confirmed impairments on memory, naming and attention/organization. The patient scored 122 (mild impairment) on the DRS. MRI demonstrated mild diffuse atrophy, more obvious along the anterior falx; no significant mesial temporal atrophy was present (Figure 2). The patient was diagnosed with multiple domain mild cognitive impairment with amnesia.¹³

Case II.2 developed dementia and apathy, dying at age 82. It is unclear whether this patient had parkinsonian features. This patient's child (Case III.2) experienced progressive apathy and difficulties performing activities around the home beginning at age 55. Initially, memory was unaffected although later it did decline. The patient's local physicians diagnosed AD. The patient exhibited features of the Kluver-Bucy syndrome, with consequent weight gain at age 58. Visual hallucinations, misidentification and parkinsonism developed around age 60, and dementia with Lewy bodies was suspected. Examination at our institution found global cognitive impairment associated with abulia and left hemiparkinsonism. MRI demonstrated 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.

Case II.3 developed memory difficulties at age 75. The patient had minimal knowledge of recent events and had stopped driving. The patient was diagnosed with probable AD. At age 76, The patient experienced rigidity and rest tremor that did not improve with carbidopa/levodopa. The patient died at age 77 from pneumonia. Neuropathological examination demonstrated FTLD-U plus NII.

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

By age 64 the patient developed acalculia and non-verbal abilities began to decline. Despite having no meaningful verbal output by age 65, the patient continued to function independently, using a credit card to make her grocery purchases because the patient could no longer write checks. Behavioral disturbances typical of FTD became evident the following year, and the patient became progressively more anxious and combative. Follow-up MRI examinations (Figure 2) documented progressive atrophy more prominently involving the left hemisphere, and most severely involving the left temporal lobe. This person died at age 70, and the neuropathologic examination demonstrated FTLD-U with NII.

Case II.4 first developed cognitive and behavioral changes at age 80. Significant decline in memory, language and attention/executive function was evident by age 83, when these problems first came to medical attention. The patient had limited knowledge of recent events and family noted dents in the car which the patient was unable to explain. The patient had lost 14 pounds, providing only vague descriptions of meals the patient claimed to prepare for herself. During examination the patient was inattentive and disoriented, having difficulties with memory, naming and executive function. Neuropsychological testing confirmed these deficits, and the score on the DRS was 84 (moderately severe impairment). Performance on the AVLT and other memory tests documented significant impairment in delayed recall. The patient's primary care physician diagnosed probable AD. The patient subsequently developed behaviors out of character for the patient's established personality, such as telling a relative, “You're too fat.” By age 84 the patient's responses consisted of one word followed by laughter; the patient produced no meaningful verbalizations and followed no commands by age 85. Bilateral upper extremity rigidity and left leg rest tremor were noted on examination. MRI at age 85 demonstrated prominent atrophy, more pronounced in the frontal and temporal lobes, as well as 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. The diagnosis was changed to FTD. The patient died at age 87, and neuropathological examination found FTLD-U plus NII with remarkably no AD pathology.

PGRN analysis in seven affected members of this kindred revealed a single base pair deletion in exon 2 (c.154delA). This frameshift mutation (p.Thr52Hisfs×2) creates a premature termination codon, likely resulting in a null allele through nonsense-mediated decay.¹

Group considerations

Table 2 summarizes demographic and clinical information regarding this kindred, grouped by generation. The mean age of onset is substantially earlier in the third generation in comparison to the second generation. Disease duration is similar, although one affected member of generation III is still living. Generation II exhibited less phenotypic heterogeneity.

Table 2.

Summary of demographics and clinical data grouped by generation

	Generation GII	Generation GIII
Number of Affected Individuals	5	3
Mean Age of Onset (yrs)	75.8	60.7
Range	69-80	55-66
Duration (yrs)	5.8	> 5
Range	2 - 7	> 5 - 10
Clinical Manifestations	3 Alzheimer's Disease	Primary Progressive Aphasia
	1 FTD	FTD/DLB features
	1 Dementia NOS	MCI
Autopsy findings	FTLD-U + NII	FTLD-U + NII

Abbreviations: FTD=frontotemporal dementia; FTLD-U + NII=frontotemporal lobar degeneration with ubiquitin positive neuronal cytoplasmic and intranuclear inclusions; LBD=Lewy body disease; MCI=mild cognitive impairment; NOS=not otherwise specified

MRI data was available in five subjects, 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 was present in case II.4, and was less prominent in the right temporal lobe in case 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 covering two or more years were available in three patients, which all showed progression of atrophy and subcortical white matter signal changes similar to what has been described in another FTDP case with a PGRN mutation.³

Discussion

The clinical descriptions of families and individuals having mutations in PGRN have occupied the clinical spectrum of FTLD - cognitive impairment (executive dysfunction and/or aphasia) and behavioral changes, variably accompanied by parkinsonism.^1-5 This likely represents the core phenotypic features, but in this family, prominent early memory impairment was a common clinical feature. Four members of this family presented with amnestic complaints and followed a course typical of AD, and this remained their final diagnosis in two. Another member of this family presented with prominent memory impairment thought to represent Alzheimer disease, although the patient later followed a course more suggestive of FTD. Although this early memory impairment was confirmed by detailed neuropsychological testing in only two individuals, the available medical records and family accounts provided ample detail regarding other individuals' early clinical courses. Personality change was an early finding in only three affected individuals. Similarly, executive dysfunction was an early finding in only two or three individuals. Thus, a majority of affected members presented with prominent early or initial memory impairment, while a distinct minority presented with early or initial behavioral/executive dysfunction.

Prominent early memory impairment is characteristic of amnestic MCI and Alzheimer's disease, and is an exclusionary criterion for the diagnosis of FTD.¹⁴ Generally, the neurofibrillary tangles in the mesial temporal lobes characteristic of Alzheimer's disease form the pathological substrate for this type of prominent memory impairment. In this family, three individuals having a clinical presentation and subsequent clinical course typical of AD were found to have FTLD-U plus NII as the pathological substrate. This clinical phenotype is distinct from that seen in other described kindreds having mutations in PGRN associated with FTLD-U NII neuropathology,⁵ and is very atypical in association with familial FTLD neuropathology in general.

Our data confirm the phenotypic heterogeneity observed within other kindreds. Several members had primarily amnestic difficulties, one member followed an early course typical of PPA, another followed the typical course of FTDP, and one presenting with amnestic complaints evolved into a clinical picture of FTD within one year. Similar heterogeneity has been reported both within families and among families with identical mutations in MAPT.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 MAPT.¹⁷

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

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

The MRI abnormalities typically reported in sporadic FTD and familial FTD have been frontotemporal cortical abnormalities varying from symmetric to markedly asymmetric atrophy.^20-22 Most descriptions have not reported subcortical white matter signal changes. One individual in this kindred had striking subcortical white matter signal change adjacent to the regions of maximal cortical atrophy, and in one other case, a milder degree of subcortical signal changes was present. MRI scans 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 small number of individuals having FTLD-U neuropathology suggested more severe and widespread frontal, temporal and also parietal atrophy among those having PGRN mutations.²³

Brain tissue was examined in six cases, 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}

Case II.1 had mixed FTLD-U plus NII, vascular and Alzheimer's disease pathologies. A recent study suggested that immunohistochemical staining for ubiquitin and/or TDP-43 may be a useful adjunct to identify FTLD-U pathology in the presence of additional pathological processes,^{24, 26} and this technique was used to confirm the presence of FTLD-U pathology in Case II.1.

As in previously reported kindreds, the pattern of inheritance was autosomal dominant. Penetrance is high, although not 100%,⁴ with at least one asymptomatic carrier identified.

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