Association of apolipoprotein epsilon 4 allele and neuropathologic findings in patients with dementia

The genetic association between apolipoprotein E gene polymorphism and Parkinson disease: A meta-Analysis of 47 studies

OBJECTIVE

Although the relationship between apolipoprotein E (ApoE) gene polymorphisms and the risk of Parkinson disease (PD) has been established, the results were inconsistent and inconclusive.

METHODS

A comprehensive search examining the association between APOE polymorphisms and PD through PubMed, Embase, Chinese National Knowledge Infrastructure (CNKI), and Cochrane Library databases was performed without published year limited.

RESULTS

A total of 47 studies with 7533 cases and 14442 controls were included in present study. The results showed statistically significant association between risk factor ApoE ε4 allele and PD in Asian population (P = .003, odds ratio, OR [95% confidence interval, CI] = 1.43 [1.13,1.80]). Genotype ε2ε4 have significantly associated with PD in Asian population (P = .004, OR [95% CI] = 4.43 [1.62,12.10]). Genotype ε3ε4 was significantly associated with PD in Latin-American population (P = .01, OR [95% CI] = 1.44 [1.08,1.91]). In addition, the frequency of the genotype ε3ε4 is lower in PD group than that in the control group in Caucasian population, and the difference of genotype ε3ε4 is also statistically significant (P = .006, OR [95% CI] = 0.86 [0.77,0.96]). Although significant heterogeneity was observed among all studies, the results were shown to be stabilized by sensitive analysis. No publish bias was observed.

CONCLUSIONS

This meta-analysis suggests that the APOE ε4, but no ε2, might be a risk factor for PD in Asian population. Furthermore, the genotype ε2ε4 may be a susceptible factor for PD in Asian population, and the genotype ε3ε4 may be a susceptible factor for PD in both Caucasian and Latin-American populations.

Amyloid beta: structure, biology and structure-based therapeutic development

Amyloid beta peptide (Aβ) is produced through the proteolytic processing of a transmembrane protein, amyloid precursor protein (APP), by β- and γ-secretases. Aβ accumulation in the brain is proposed to be an early toxic event in the pathogenesis of Alzheimer's disease, which is the most common form of dementia associated with plaques and tangles in the brain. Currently, it is unclear what the physiological and pathological forms of Aβ are and by what mechanism Aβ causes dementia. Moreover, there are no efficient drugs to stop or reverse the progression of Alzheimer's disease. In this paper, we review the structures, biological functions, and neurotoxicity role of Aβ. We also discuss the potential receptors that interact with Aβ and mediate Aβ intake, clearance, and metabolism. Additionally, we summarize the therapeutic developments and recent advances of different strategies for treating Alzheimer's disease. Finally, we will report on the progress in searching for novel, potentially effective agents as well as selected promising strategies for the treatment of Alzheimer's disease. These prospects include agents acting on Aβ, its receptors and tau protein, such as small molecules, vaccines and antibodies against Aβ; inhibitors or modulators of β- and γ-secretase; Aβ-degrading proteases; tau protein inhibitors and vaccines; amyloid dyes and microRNAs.

Biomarkers of cognitive decline in Parkinson's disease

Cognitive impairment is a frequent and devastating non-motor symptom of Parkinson's disease (PD). Impaired cognition has a major impact on either quality of life or mortality in patients with PD. Notably, the rate of cognitive decline and pattern of early cognitive deficits in PD are highly variable between individuals. Given that the underlying mechanisms of cognitive decline or dementia associated with PD remain unclear, there is currently no mechanism-based treatment available. Identification of biological markers, including neuroimaging, biofluids and common genetic variants, that account for the heterogeneity of PD related cognitive decline could provide important insights into the pathological processes that underlie cognitive impairment in PD. These combined biomarker approaches will enable early diagnosis and provide indicators of cognitive progression in PD patients. This review summarizes recent advances in the development of biomarkers for cognitive impairments in PD.

Low Density Lipoprotein Receptor-Related Protein and Apolipoprotein E Expression is Altered in Schizophrenia

Our recent microarray study reported altered mRNA expression of several low density lipoprotein receptor-related proteins (LRP) associated with the first 4 years following diagnosis with schizophrenia. Whilst this finding is novel, apolipoprotein E (APOE), which mediates its activity through LRPs, has been reported by several studies to be altered in brains of subjects with schizophrenia. We used qPCR to measure the expression of LRP2, LRP4, LRP6, LRP8, LRP10 and LRP12 mRNA in Brodmann's area (BA) 46 of the dorsolateral prefrontal cortex in 15 subjects with short duration of illness schizophrenia (SDS) and 15 pair matched controls. We also used Western blotting to measure APOE protein expression in BA46 from these subjects. Amongst the LRPs examined, LRP10 expression was significantly increased (P = 0.03) and LRP12 was significantly decreased (P < 0.01) in SDS. APOE protein expression was also increased in SDS (P = 0.01). No other marker examined in this study was altered with diagnosis. Our data supports a role for distinct members of the LRP family in the pathology of schizophrenia and adds weight to the hypothesis that aberrant apolipoprotein signaling is involved in the early stages of schizophrenia.

Absence of the apolipoprotein E ε4 allele is associated with working memory impairment in Parkinson's disease

The apolipoprotein E (APOE) epsilon4 allele has been associated with an increased risk of Alzheimer's disease (AD) and weaker episodic memory among elderly. Although this APOE allele has been linked to earlier onset of Parkinson's disease (PD), an association with dementia in PD has been only inconsistently demonstrated. Given the heterogeneity of cognitive impairment patterns in PD, this study sought to determine whether an association exists between APOE genotype and specific cognitive deficits in PD. The neuropsychological test performance of 42 PD patients without an epsilon4 allele (PD-Non4) and of 20 with at least one epsilon4 allele (PD-epsilon4) was compared to that of 146 elderly control subjects (NC). The PD groups were comparable in overall severity of cognitive impairment and disease duration, but the PD-epsilon4 group was younger, had an earlier disease onset, and contained a higher proportion of persons with dementia. Both PD groups showed wide-ranging cognitive impairments relative to NC. Once age differences between groups were controlled for, the PD groups generally did not differ from each other in cognitive performance. However, only the PD-Non4 group demonstrated working memory/attention impairments (digit span, visual span, Trailmaking test) relative to the NC group. Results suggest that the APOE genotype may influence the cognitive phenotype of PD, and specifically that absence of the epsilon4 allele is associated with working memory impairment. Additionally, results are consistent with prior findings showing an association between the epsilon4 allele and earlier onset of PD and presence of dementia.

Dendritic cells in multiple sclerosis lesions: maturation stage, myelin uptake, and interaction with proliferating T cells

In multiple sclerosis (MS), dendritic cells (DCs) recruited to the central nervous system (CNS) are thought to be involved in the regulation of autoimmune responses directed against myelin antigens. To better understand the role of DCs in CNS inflammation, we performed a detailed immunohistochemical analysis of DC maturation markers and of DC relationship to CNS-infiltrating T cells in autopsy brain tissue of patients with MS. We also investigated the presence of DCs containing myelin debris in MS lesions. Myeloid DC subsets were identified using the following markers: CD1a for immature DCs; DC-SIGN for immature and mature DCs; and fascin, CD83, DC-LAMP, and CCR7 for mature DCs. The most common finding was the presence of cells expressing DC-SIGN and containing myelin components in the perivascular cuffs of early active and chronic (both active and inactive) MS lesions. Perivascular CD1a DCs were detected in active lesions in only one of 10 patients with MS who were examined. Although less numerous than DC-SIGN DCs, cells expressing mature DC markers were consistently detected in the inflamed meninges and perivascular cuffs of most active lesions examined. CCR7 immunostaining was predominantly confined to activated microglia at the lesion edges. Some perivascular DC-SIGN cells were found in close proximity to or contacting rare proliferating lymphocytes, most of which expressed the DC-SIGN ligand ICAM-3 and CD8. These data suggest that DCs recruited and maturing in MS lesions, where self-antigens are made available by continuous myelin destruction, may contribute to the local activation and expansion of presumably pathogenic T cells.

Genetic association between the APOE*4 allele and Lewy bodies in Alzheimer disease

OBJECTIVE

To explore the association between APOE*4 and pathologically confirmed cases of the Lewy body (LB) variant of Alzheimer disease (AD).

METHODS

With use of alpha-synuclein (AS) immunohistochemistry, LBs were detected in 74 of 131 (56.5%) of the AD + LB cases; the remaining 57 cases (43.5%) did not have LBs.

RESULTS

There were no differences in gender or age between Caucasian subjects with AD + LB or AD alone or control subjects. The APOE*4 allele frequency was highest in the AD + LB group (47.3%; 95% CI = 37.8 to 57.0%), intermediate in the AD-alone group (35.1%; 95% CI = 25.3 to 46.3%), and lowest in the control group (14.2%; 95% CI = 10.5 to 18.9%). With use of logistic regression analysis, the odds of having AD + LB vs AD alone were 2.1-fold (95% CI = 1.0 to 4.5, p = 0.055) greater in persons with an APOE*4 allele than in those without an APOE*4 allele.

CONCLUSION

The APOE*4 allele is associated with the presence of concomitant Lewy bodies in Alzheimer disease.

ApoE −491A/T Promoter Polymorphism is not an Independent Risk Factor, but Associated with the ε4 Allele in Hungarian Alzheimer’s Dementia Population

Apolipoprotein E gene (Apo(epsilon)) has three common alleles (epsilon2, epsilon3, and epsilon4), of which epsilon4 has been shown to be associated with an increased risk for Alzheimer's disease (AD). Possible additional genetic factors, like the -491A variant of ApoE promoter may modify the development of AD, independently of the ApoE allele status. The objective of this study was to investigate whether A/T allelic polymorphism at site-491 of the ApoE promoter is associated with AD in a Hungarian population. The genomic DNA isolated from peripheral blood lymphocytes of 52 late-onset AD and 53 control individuals was used as a template for the two examined polymorphisms and PCR assay was applied. The epsilon4 allele was significantly over-represented in the AD group (28%) as compared with the control population (7%). No significant differences have been found between the control and the AD populations regarding the occurrence of the promoter A allele frequencies (control: 77%, AD: 70%). However, the AA genotype was more frequent in the AD group (48%) than in the control (10%) when the presence of epsilon4 allele was also considered. It is unlikely therefore that the -491A variant of the ApoE promoter gene is an independent risk factor in the Hungarian AD population, but a linkage disequilibrium exists between the two examined mutations.

Polymorphism in candidate genes: implications for the risk and treatment of idiopathic Parkinson's disease

Idiopathic Parkinson's disease (IPD) is a progressive neurodegenerative disorder for which no restorative or neuroprotective therapy is available. Interest has recently been directed to association studies on polymorphisms of various genes, mainly those related to dopamine metabolism and transport, and their effect on response to PD, which includes primarily levodopa and dopaminomimetics. Approximately 15-20% of patients with PD do not respond to levodopa, and the majority of those who do respond develop adverse fluctuations in motor response, primarily levodopa-induced dyskinesias. This review summarizes the influence of polymorphisms in various genes on the relative risk of IPD and on levodopa efficacy. It focuses on the importance of well-designed polymorphism studies that include large samples of patients with IPD and tightly matched controls and use identical methodologies. Valid data on such polymorphisms might increase the efficacy of levodopa, decrease its side effects, and reduce the occurrence of levodopa-induced dyskinesias. They might also provide a novel diagnostic tool for PD.

Progress in clinical neurosciences: Parkinson's disease with dementia and dementia with Lewy bodies

Dementia occurs in up to 30% of people with Parkinson's disease and is a major cause of disability. Pathologically, Parkinson's dementia, where dementia follows the onset of parkinsonism by at least one year, overlaps with dementia with Lewy bodies. We review the functional impact, definitions, neuropsychology, epidemiology and pathophysiology of Parkinson's dementia, dementia with Lewy bodies and their overlap. Associated psychiatric and imaging findings are also considered. Lastly, current and emerging approaches to assessment and treatment in patients with these Lewy body associated dementias are presented.

Cognitive decline in schizophrenics with Alzheimer's disease: a mini-review of neuropsychological and neuropathological studies

Cognitive decline in elderly schizophrenic patients is an important clinical symptom, but it is often difficult to analyze in detail due to the patient's original residual psychotic symptoms. In this article, the authors provide neuropsychological and neuropathological research information about cognitive decline in elderly schizophrenic patients, especially with reference to Alzheimer's disease (AD). Neuropsychological and neuropathological reports about cognitive impairments are reviewed. The effect of long-term antipsychotic medication upon cognitive function is also discussed. As a result, it is apparent that elderly schizophrenic patients often show cognitive impairments, however, such impairments do not have the characteristics of progressive degenerative illnesses such as AD, and the speed of their progress is very slow. Neuropathological studies have shown that AD brain pathology appears no more frequently among schizophrenic patients than in the normal population. Since making a diagnosis of AD means that the progressive deterioration not only of cognitive function, but also of physical ability, paralleling the degeneration of the central nervous system, can be expected within a few years and appropriate care will be required. One should be very cautious in adding a diagnosis of AD to elderly schizophrenic patients with cognitive impairments.

Apolipoprotein E polymorphism in Pick's disease and in Huntington's disease

The polymorphism of apolipoprotein E (apoE) has been recognized as a genetic risk factor in different neurodegenerative disorders, with or without tau protein- related neuropathology, but few published epidemiological data are available as concerns the association of different apoE alleles with two relatively rare forms of dementia, Pick's disease (PiD) and Huntington's disease (HD). In this study the frequency of the apoE4 allele was examined in 36 persons with histopathologically proven PiD and compared with that of the apoE genotype in 28 HD probands and 79 aged healthy controls. The E4 allele was overrepresented selectively in PiD (42%) as compared with the control population (7%). No such association was found for HD probands (9%). This finding lends further support to the hypothesis that the E4 genotype is not an Alzheimer's disease specific susceptibility factor, and that it could be present in diverse dementing disorders with tau protein related neuropathology, such as PiD.

beta-amyloid load is not influenced by the severity of cardiovascular disease in aged and demented patients

BACKGROUND AND PURPOSE

This study was conducted to analyze the association between reported risk factors for Alzheimer's disease, apolipoprotein E epsilon4 allele, and cardiovascular disease and neuropathological changes essential for the diagnosis of Alzheimer's disease.

METHODS

Our data are based on clinical and postmortem evaluations of a cohort of nondemented (n=118) and demented (n=107) individuals. A cardiovascular index was calculated at autopsy to estimate the extent of cardiovascular disease. Neuropathological lesions such as senile/neuritic plaques, neurofibrillary tangles, beta-amyloid load, cerebral amyloid angiopathy, and the load of paired helical filaments were determined.

RESULTS

The aforementioned neuropathological lesions did not show any positive significant correlation with cardiovascular index. In contrast, the extent of Alzheimer's lesions was significantly higher in those nondemented and demented patients carrying the apolipoprotein E epsilon4 allele than in those without this allele.

CONCLUSIONS

Our results demonstrate that the apolipoprotein E epsilon4 allele, but not cardiovascular disease, indeed influences the extent of Alzheimer's lesions seen in the brain tissue of demented patients as well as asymptomatic controls.

Genetic epidemiology of Parkinson's disease

The cause of Parkinson's disease (PD) is unknown. The major risk factors identified to date are family history, age, and elements of rural living. Nearly one-third of all PD cases are familial, a small subset of which appears autosomal dominant; however, the majority exhibit no clear inheritance pattern. Autosomal dominant PD is genetically heterogeneous: two PD genes have been mapped to chromosomes 2 and 4 and there may be additional as yet unidentified genes. The common forms of PD-both familial and sporadic cases-appear to involve a complex interplay of genetic susceptibility and environmental exposure. The observations that rural residence and pesticide exposure increase the risk of developing PD, and that a synthetic drug, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, can cause parkinsonism, suggest that at least a subset of PD may be caused by a toxin. Furthermore, modest but significant associations have been reported between PD susceptibility and genes that regulate metabolism of drugs and neurotoxins. There is also evidence for mitochondrial dysfunction in PD, a finding that was recently traced to anomalies in mitochondrial DNA. At the present time, the genetics of PD appear to be complex, involving multiple nuclear genes and possibly mitochondrial genes as well.

Apolipoprotein E is present in primary localized cutaneous amyloidosis

Apolipoprotein E (apoE) is one of the amyloid associated proteins that is found in the amyloid plaque of Alzheimer's disease and systemic amyloidosis. ApoE might play an important part in the etiology of Alzheimer's disease by functioning as a "pathologic chaperone" to promote the formation of amyloid filaments. In this study, we investigated whether apoE is associated with amyloid deposits of primary localized cutaneous amyloidosis using immunohistochemistry, immunogold electron microscopy, and immunoblotting. The subjects consisted of 12 patients with lichen amyloidosus and one patient with macular amyloidosis. Light microscopically, amyloid deposits in the dermal papillae were round in shape and stained with Congo red. Immunohistochemically, apoE was detected in amyloid deposits in all the cases examined. Immunogold electron microscopy showed apoE immunoreactivity on the amyloid deposition. Immunoblots of amyloid-positive skin showed 35K and 14K proteins, which were taken to be apoE and its fragment, respectively. In normal skin extract, only the 35K protein was detected by the anti-human apoE. Moreover, the intensity of the amyloid-positive skin sample was stronger than that of the normal skin sample. Monoclonal anti-cytokeratin antibody reacted with the 45K protein of the amyloid-positive skin extract. These results indicate that apoE is a component of primary localized cutaneous amyloidosis, and that it might play an important role in primary localized cutaneous amyloidosis.

Autopsy study of Alzheimer's disease brain pathology in schizophrenia

The brains of 125 schizophrenic patients (DSM-IV criteria) without other major diseases likely to affect brain morphology were examined at autopsy in our hospital for an evaluation of the number of neurofibrillary tangles (NFT) and senile plaques (SP) as indicators of the incidence of Alzheimer's disease (AD) brain pathology. The clinical degree of dementia and the presence or absence of delirium and Parkinsonism were determined in a review of the patients' charts. No significant difference in the degree of AD brain pathology between the 12 schizophrenics more than 75 years old and 12 age-matched normal controls was present. We conclude that AD pathology seems to be no more frequent among schizophrenic patients than in the normal population, and that the severe cognitive impairment observed in schizophrenics is based on neither neuronal degeneration nor neuronal loss like that occurring in AD. We believe that future morphological studies of cognitive impairments in schizophrenics will require a more detailed investigation at the receptor level.

Dementia with Lewy bodies. A distinct non-Alzheimer dementia syndrome?

Lewy body formation is central to the pathological phenotype of a spectrum of disorders. The most familiar of these is the extrapyramidal syndrome of idiopathic Lewy-body Parkinson's disease (PD). Studies of dementia in the elderly suggest that another manifestation of Lewy body pathology is equally or more common than Parkinson's disease. This syndrome of Dementia with Lewy bodies (DLB) has been given a number of diagnostic labels and is characterised by dementia, relatively mild parkinsonism, visual hallucinations, and fluctuations in conscious level. Although many of these features can arise in Parkinson's disease, the patients with DLB tend to have early neuropsychiatric features which predominate the clinical picture, and the diagnosis of the syndrome in practice is more concerned with the differential diagnosis of Alzheimer's disease (AD). Distinction from AD has clinical importance because of potentially differing therapeutic implications. Diagnostic guidelines for the clinical diagnosis and pathological evaluation of DLB are reviewed. Research into the disorder has centered around characterising the clinical, neuropsychological, pathological, neurochemical and genetic relationships with Alzheimer's disease on the one hand, and Parkinson's disease on the other. Many cases of DLB have prominent pathological features of AD and there are some shared genetic risk factors. Differences from the pathology of PD are predominantly quantitative rather than qualitative and evidence is discussed which suggests that DLB represents a clinicopathological syndrome within the spectrum of Lewy body disorders. The possibility that the syndrome represents a chance association of PD and AD is not supported by published studies.

Autosomal dominant dementia with widespread neurofibrillary tangles

Several familial dementing conditions with atypical features have been characterized, but only rarely is the neuropathology dominated solely by neurofibrillary lesions. We present a Midwestern American pedigree spanning four generations in which 15 individuals were affected by early-onset dementia with long disease duration, with an autosomal dominant inheritance pattern, and with tau-rich neurofibrillary pathology found in the brain post mortem. The average age at presentation was 55 years with gradual onset and progression of memory loss and personality change. After 30 years' disease duration, the proband's neuropathologic examination demonstrated abundant intraneuronal neurofibrillary tangles (NFTs) involving the hippocampus, pallidum, subthalamic nucleus, substantia nigra, pons, and medulla. Only sparse neocortical tangles were present and amyloid plaques were absent. The tangles were recognized by antibodies specific for phosphorylation-independent (Tau-2, T46, 133, and Alz-50) and phosphorylation-dependent epitopes (AT8, T3P, PHF-1, 12E8, AT6, AT18, AT30) in tau proteins. Electron microscopy of NFTs in the dentate gyrus and midbrain demonstrated paired helical filaments. Although the clinical phenotype resembles Alzheimer's disease, and the neuropathologic phenotype resembles progressive supranuclear palsy, an alternative consideration is that this familial disorder may be a new or distinct disease entity.

[Genetics of Alzheimer's disease]

This review reports the different genetic factors that have been identified either as risk factor for Alzheimer's disease (AD) or directly causing the disease. First are reviewed epidemiological data and biological mechanisms about the apoplipoprotein E gene allele epsilon 4 that is a major risk factor for Alzheimer's disease. The second part describes the mutations responsible for early-onset autosomal dominant AD found in three different genes. The gene located on chromosome 21 encodes the amyloid precusor protein (APP). The presenilin 1 and presenilin 2 genes, located on chromosome 14 and 1 respectively, encode not yet known membrane proteins.

Tau protein and apolipoprotein E in CSF diagnostics of Alzheimer's disease: impact on non Alzheimer's dementia?

Tau protein and apolipoprotein E are suggested to be biochemically related to neurofibrillary tangles and senile plaques in Alzheimer's disease (AD) brains. They can be detected as immunoreactive material (total tau immunoreactivity [TTIR] and apolipoprotein E-immunoreactivity [ApoEIR]) in the cerebrospinal fluid (CSF). TTIR and ApoE-IR have been measured in ex vivo lumbar and post mortem ventricular CSF in AD, other neurological diseases without cognitive impairment, elderly depressive patients, and young and elderly controls. In lumbar CSF, there was a highly significant increase of TTIR and a minor, insignificant decrease of ApoE-IR in CSF of AD patients. The latter result was also found in ventricular CSF, whereas TTIR showed no significant difference between groups in the rostral CSF compartment. As depressive periods in the elderly may mimick a dementing process, these findings contribute to the differential diagnosis of these disorders by showing a different neurobiochemical CSF profile. Work in progress will include a variety of non-Alzheimer's dementias and possibly will further increase the value of CSF investigation in neurodegenerative disorders.

Structural basis of dementia in neurodegenerative disorders

Progressive dementia syndromes in adults are caused by a number of conditions associated with different structural lesions of the brain. In most clinical and autopsy series, senile dementia of the Alzheimer type is the most common cause of mental decline in the elderly accounting for up to 90%, whereas degenerative non-Alzheimer dementias range from 7 to 30% (mean 8-10%). They include a variety of disorders featured morphologically by neuron and synapse loss and gliosis, often associated with cytopathological changes involving specific cortical and subcortical circuits. These neuronal/glial inclusions and neuritic alterations show characteristic immunoreactions and ultrastructure indicating cytoskeletal mismetabolism. They are important diagnostic sign posts that, in addition to the distribution pattern of degenerative changes, indicate specific vulnerability of neuronal populations, but their pathogenic role and contribution to mental decline are still poorly understood. In some degenerative disorders no such cytopathological hallmarks have been observed; a small number is genetically determined. While in Alzheimer's disease (AD) mental decline is mainly related to synaptic and neuritic pathologies, other degenerative disorders show variable substrates of dementia involving different cortical and/or subcortical circuits which may or may not be superimposed by cortical Alzheimer lesions. In most demented patients with Lewy body disorders (Parkinson's disease, Lewy body dementia), they show similar distribution as in AD, while in Progressive Supranuclear Palsy (PSP), mainly prefrontal areas are involved. Lobar atrophies, increasingly apparent as causes of dementia, show fronto-temporal cortical neuron loss, spongiosis and gliosis with or without neuronal inclusions (Pick bodies) and ballooned cells, while dementing motor neuron disease and multisystem atrophies reveal ubiquitinated neuronal and oligodendroglial inclusions. There are overlaps or suggested relationships between some neurodegenerative disorders, e.g. between corticobasal degeneration, PSP and Pick's atrophy. In many of these disorders with involvement of the basal ganglia, degeneration of striatofrontal and hippocampo-cortical loops are important factors of mental decline which may be associated with isocortical neuronal degeneration and synapse loss or are superimposed by cortical AD pathology.