Candidate genes showing no evidence for association or linkage with Alzheimer's disease using family-based methodologies

Alzheimer's disease (AD) is a genetically complex and heterogeneous disorder. To date, a large number of candidate genes have been associated with the disease, however none of these findings has been consistently replicated in independent datasets. In this study we report the results of family-based analyses for polymorphisms of five such candidates on chromosomes 2 (interleukin-1beta, IL-1B), 3 (butyrylcholinesterase, BCHE), 11 (cathepsin D, CTSD; Fe65, APBB1) and 12 (lipoprotein receptor-related protein-1, LRP1) that were all suggested to be associated with AD in recent case-control studies. To minimize the possibility of spurious findings due to population admixture, we used a family-based design applying the sibship disequilibrium test (SDT) as well as two-point parametric linkage analyses on families from the National Institute of Mental Health (NIMH) Genetics Initiative. Contrary to the initial reports, none of the polymorphisms that were analyzed showed evidence for association or linkage with AD in our families. Our results suggest that the previously reported associations from case-control studies are either (a) false positive results, e.g. due to type I error or population admixture, (b) smaller than initially proposed, or (c) due to linkage disequilibrium with an as yet unidentified polymorphism nearby.

Enkephalinase: selective inhibitors and partial characterization

There are at least two types of enzymes in brain, endopeptidases and aminopeptidases, which metabolize enkephalins. Evidence is presented to suggest that enkephalinase, an endopeptidase cleaving at the Gly-Phe bond, is specific for the endogenous enkephalinergic system. Selective inhibitors are described for each enzyme. These are parachloromercuriphenylsulfonic acid and puromycin in the case of aminopeptidases and various enkephalin fragments in the case of enkephalinase. Some characteristics of the two types of enzymes are described. Enkephalinase has many properties in common with the well-characterized brain angiotensin-converting enzyme. These two enzymes, however, behaved differently when tested for chloride dependence, for activity in several buffers and for susceptibility to specific inhibitors.

Unipolar relatives in bipolar pedigrees: a search for indicators of underlying bipolarity

In an effort to identify features indicative of underlying bipolarity within the unipolar relatives of bipolar probands, we compared unipolar relatives of bipolars with unipolar relatives of unipolars. Using data from the Collaborative Study of the Psychobiology of Depression, we compared a number of demographic and clinical features individually, and then developed a logistic regression model for the differences found. Unipolar relatives of bipolars were somewhat more likely to be male and to have subthreshold bipolar features, and less likely to have panic symptoms. In addition, they had a small but significant decrease in the number of depressive symptoms and a large decrease in all treatment indicators. A multiple logistic regression model for these differences was highly significant, but had limited ability to discriminate between the two groups. These differences are not large enough to effectively discriminate between the groups for the purposes of classification. These particular results may result from a number of factors, most likely the choice of comparison group. Nonetheless, the work demonstrates a potential method for the construction of caseness indices for use in genetic studies of bipolar and other psychiatric disorders.

The Anxiety Sensitivity Index for Children: factor structure and relation to panic symptoms in an adolescent sample

This study examines the factor structure underlying the Anxiety Sensitivity Index for Children (ASIC. J Anxiety Disord, 12 (1998) 307) in an adolescent sample. Three-hundred-and-eight adolescents, aged 12 to 18, completed the ASIC and measures of anxiety and depression. Factor analysis of the ASIC items resulted in a two-factor structure that is similar to that reported by Laurent et al. These two factors included a physical concerns dimension and a mental concerns dimension similar to those found in studies of adult anxiety sensitivity. Subscales measuring these two factors demonstrated concurrent validity, showing particularly close associations with measures of panic symptoms. In addition, both of these subscales showed incremental validity in predicting panic symptoms after controlling for the other anxiety sensitivity subscale and a measure of depression. These results provide evidence that the anxiety sensitivity construct is applicable during adolescence and support the use of the ASIC.

No evidence for genetic association or linkage of the cathepsin D (CTSD) exon 2 polymorphism and Alzheimer disease

Two recent case-control studies have suggested a strong association of a missense polymorphism in exon 2 of the cathepsin D gene (CTSD) and Alzheimer disease (AD). However, these findings were not confirmed in another independent study. We analyzed this polymorphism in two large and independent AD study populations and did not detect an association between CTSD and AD. The first sample was family-based and included 436 subjects from 134 sibships discordant for AD that were analyzed using the sibship disequilibrium test (SDT, p = 0.68) and the sib transmission/disequilibrium test (Sib-TDT, p = 0.81). The second sample of 200 AD cases and 182 cognitively normal controls also failed to show significant differences in the allele or genotype distribution in cases versus controls (chi2, p = 0.91 and p = 0.88, respectively). In addition, two-point linkage analyses in an enlarged family sample (n = 670) did not show evidence for linkage of the chromosomal region around CTSD. Thus, our analyses on more than 800 subjects suggest that if an association between the CTSD exon 2 polymorphism and AD exists, it is likely to be smaller than previously reported.

Specificity in the familial aggregation of overt and covert conduct disorder symptoms in a referred attention-deficit hyperactivity disorder sample

BACKGROUND

To examine the familial associations of overt and covert antisocial behavior within the diagnosis of conduct disorder (CD) in families ascertained by referred children with attention-deficit hyperactivity disorder (ADHD), and to test if these familial associations differed between male and female probands.

METHOD

Subjects were clinically-referred male and female ADHD children (n = 273) and their first-degree biological relatives (n = 807). Scores for overt and covert conduct problems were calculated by summing the DSM-III-R conduct disorder symptoms, as derived from structured diagnostic interviews. Familial aggregation analyses were conducted with multivariate regression modeling methodology.

RESULTS

Proband overt scores significantly predicted the overt scores of their relatives, and proband covert scores significantly predicted the covert scores of their relatives. There was no evidence of covert symptom scores predicting overt scores or vice versa. There was some evidence that the aggregation of covert symptoms was stronger in the families of female probands.

CONCLUSIONS

These results provide preliminary evidence that overt and covert conduct disorder symptoms are independently transmitted through families and may represent distinct familial syndromes.

Association tests for traits with variable age at onset

This paper is concerned with testing association between marker genotypes and traits with variable age at onset. Two methods are proposed, one which makes use of both age-at-ascertainment and age-at-onset information, and one which may be applied when only age-at-ascertainment information is available. (Here, by age-at-ascertainment, is meant the subject's age when presence of onset and age at onset are determined; for subjects who have died or are otherwise censored before ascertainment, the censoring time should be used instead). Adjustment for confounding due to population stratification is carried out by conditioning on observed traits and parental genotypes, or, if complete parental genotypes are not available, by conditioning on observed traits and the minimal sufficient statistics under the null hypothesis for the parental genotypes. Proportional hazards regression models and logistic regression models are used to motivate the methods, but correct type I error rates result even if the models are not correct. An illustrative example is described.

Unipolar relatives in bipolar pedigrees: a search for elusive indicators of underlying bipolarity

In an effort to identify features indicative of underlying bipolarity within the unipolar relatives of bipolar probands, we compared unipolar relatives of bipolars with unipolar relatives of controls. Using data from the Yale-NIMH Collaborative Study of Depression, we compared a number of demographic and clinical features individually, and then developed a logistic regression model for the differences found. Unipolar relatives of bipolars were generally similar to relatives of controls, but they were older and more likely to suffer from more severe, even psychotic, depression, and somewhat less likely to report a brief transition into their illness. A multiple logistic regression model for observed differences was highly statistically significant, but had limited ability to discriminate effectively between the two groups. These findings suggest that more stringent diagnostic criteria might be beneficial if unipolar relatives are counted as affected in linkage studies of bipolar disorder. The ability of this strategy to improve the "clinical phenotype" is limited, however, and other approaches may be needed to identify features of underlying bipolarity and thus to define "caseness" for unipolar relatives in linkage analyses of bipolar disorder.

PEN2 is not a genetic risk factor for Alzheimer's disease in a large family sample

PEN2 is a reasonable Alzheimer's disease (AD) candidate gene because it is a necessary component of the gamma-secretase complex that generates beta-amyloid peptide. Moreover, its gene (PEN2) maps to a highly significant linkage region on chromosome 19q13. Four common polymorphisms in PEN2 were tested for genetic association with AD in a large and carefully ascertained AD family sample (789 subjects from 202 nuclear families) using single-locus and haplotype-based analyses. These results do not suggest PEN2 to be a major AD risk factor.

Further evidence for LBP-1c/CP2/LSF association in Alzheimer's disease families

OBJECTIVES

Several studies suggested chromosome 12 harbours an Alzheimer's disease (AD) risk factor gene. Significant association of a single nucleotide polymorphism (SNP) in the 3' UTR of transcription factor CP2 (LBP-1c/CP2/LSF or TFCP2) at 12q13 was reported in three independent case-control studies, but no family based analyses have been performed to date.

METHODS

Genotypes for three SNPs were generated in two independent AD family samples. A meta-analysis on all published case-control studies was also performed.

RESULTS

The A allele of the 3' UTR SNP was associated with increased risk for AD in one sample (odds ratio (OR) 2.1, 95% confidence interval (95% CI) 1.1 to 4.3), but not in the other, possibly due to low power. Haplotype analyses showed that this allele is part of a putative risk-haplotype overtransmitted to affected individuals in one sample and in both samples combined. Meta-analysis of the previously associated 3' UTR SNP showed a trend towards a protective effect of the A allele in AD (OR 0.73, 95% CI 0.5 to 1.1).

CONCLUSIONS

This is the first study to examine LBP-1c/CP2/LSF in AD families, and the fifth to independently show significant association. While our results support a role of this gene in AD pathogenesis, the direction of the effect remains uncertain, possibly indicating linkage disequilibrium with another variant nearby.

Evidence against association of the FE65 gene (APBB1) intron 13 polymorphism in Alzheimer's patients

A genetic polymorphism in intron 13 of the FE65 gene (APBB1) was reported to be associated with Alzheimer's disease (AD). Our analyses of this polymorphism, both in a family-based or a case-control sample, fail to support the association between the FE65 intron 13 polymorphism and AD. We performed the sibship disequilibrium test (SDT, P=0.77) and the sib transmission/disequilibrium test (Sib-TDT, P=0.56) in a family-based study which included 526 subjects from 158 sibships. In addition, we compared the genotype and allele frequencies of this biallelic polymorphism in 311 AD patients to those of a control group consisting of 260 subjects and found no significant difference (chi(2), P=0.847 and P=0.586, respectively). Furthermore, our two-point linkage analysis in a family-based sample was in agreement with a genome wide scan for linkage to AD and showed no evidence for linkage to the short arm of chromosome 11 where the FE65 gene is located. We conclude that the association of the FE65 intron 13 polymorphism with AD, if any, is smaller than previously reported.

Maintenance treatment of major depression: a review of the literature

This review was undertaken to assess the indications for and efficacy of maintenance treatments for major depression. It was based on a search of the medical literature and a review of randomized clinical trials. The literature shows that antidepressant medications and, to a lesser extent, psychotherapy are both effective in preventing recurrence of major depression. Lithium and carbamazepine may also be effective. Antidepressant medications are probably more effective at full therapeutic doses than at the lower doses initially advised for maintenance treatment. Based on this review, maintenance treatment should be considered for any patient with recurrent major depression. It is clearly indicated in individuals with multiple frequent episodes. Patients with less-severe illness must weight the risks and benefits of treatment in light of their earlier course and symptoms, the current impact of treatment, and the likely future impact of additional episodes.

Bridging from clinical endpoints to estimates of treatment value for external decision makers

AIM

While clinical endpoints provide important information on the efficacy of treatment in controlled conditions, they often are not relevant to decision makers trying to gauge the potential economic impact or value of new treatments. Therefore, it is often necessary to translate changes in cognition, function or behavior into changes in cost or other measures, which can be problematic if not conducted in a transparent manner. The Dependence Scale (DS), which measures the level of assistance a patient requires due to AD-related deficits, may provide a useful measure of the impact of AD progression in a way that is relevant to patients, providers and payers, by linking clinical endpoints to estimates of cost effectiveness or value. The aim of this analysis was to test the association of the DS to clinical endpoints and AD-related costs.

METHOD

The relationship between DS score and other endpoints was explored using the Predictors Study, a large, multi-center cohort of patients with probable AD followed annually for four years. Enrollment required a modified Mini-Mental State Examination (mMMS) score >or= 30, equivalent to a score of approximately >or= 16 on the MMSE. DS summated scores (range: 0- 15) were compared to measures of cognition (MMSE), function (Blessed Dementia Rating Scale, BDRS, 0-17), behavior, extrapyramidal symptoms (EPS), and psychotic symptoms (illusions, delusions or hallucinations). Also, estimates for total cost (sum of direct medical cost, direct non-medical cost, and cost of informal caregivers' time) were compared to DS scores.

RESULTS

For the 172 patients in the analysis, mean baseline scores were: DS: 5.2 (SD: 2.0), MMSE: 23.0 (SD: 3.5), BDRS: 2.9 (SD: 1.3), EPS: 10.8%, behavior: 28.9% psychotic symptoms: 21.1%. After 4 years, mean scores were: DS: 8.9 (SD: 2.9), MMSE: 17.2 (SD: 4.7), BDRS: 5.2 (SD: 1.4), EPS: 37.5%, behavior: 60.0%, psychotic symptoms: 46.7%. At baseline, DS scores were significantly correlated with MMSE (r=-0.299, p < 0.01), BDRS (r=0.610, p < 0.01), behavior (r=.2633, p=0.0005), EPS (r=0.1910, p=0.0137) and psychotic symptoms (r=0.253, p < 0.01); and at 4-year follow-up, DS scores were significantly correlated with MMSE (r=-0.3705, p=0.017), BDRS (r=0.6982, p < 0.001). Correlations between DS and behavior (-0.0085, p=0.96), EPS (r=0.3824, p=0.0794), psychotic symptoms (r=0.130, ns) were not statistically significant at follow-up. DS scores were also significantly correlated with total costs at baseline (r=0.2615, p=0.0003) and follow-up (r=0.3359, p=0.0318).

DISCUSSION

AD is associated with deficits in cognition, function and behavior, thus it is imperative that these constructs are assessed in trials of AD treatment. However, assessing multiple endpoints can lead to confusion for decision makers if treatments do not impact all endpoints similarly, especially if the measures are not used typically in practice. One potential method for translating these deficits into a more meaningful outcome would be to identify a separate construct, one that takes a broader view of the overall impact of the disease. Patient dependence, as measured by the DS, would appear to be a reasonable choice - it is associated with the three clinical endpoints, as well as measures of cost (medical and informal), thereby providing a bridge between measures of clinical efficacy and value in a single, transparent measure.

Cholecystokinin B receptor antagonists enhance the locomotor response to the N-methyl-D-aspartate antagonists phencyclidine and dizocilpine maleate

The cholecystokinin antagonists L-740,093, L-365,260, LY-288513 and CI988, which are all selective for the cholecystokininB receptor subtype, were examined for their ability to modulate locomotor activity induced by the non-competitive N-methyl-D-aspartate receptor antagonists phencyclidine and dizocilpine maleate (MK-801) in habituated rats. It was found that the locomotor effects (motility, locomotion) produced by subcutaneous administration of phencyclidine (2 mg/kg) were significantly potentiated by intraperitoneal (i.p.) administration of L-740,093 (1 mg/kg), L-365,260 (10 mg/kg), LY-288513 (10 mg/kg), but not CI-988 (10 mg/kg). Locomotor activity induced by subcutaneous administration of MK-801 (0.15 mg/kg) was potentiated by intraperitoneal L-740,093 (0.3, 1 and 3 mg/kg). L-740,093, L-365,260, LY-288513 and CI-988 administered alone did not alter spontaneous locomotor activity (motility) as compared to vehicle/saline controls. However, when these antagonists were administered to naive, unhabituated rats, L-365,260 and LY-288513 caused a significant reduction in motility compared to the vehicle control. These findings suggest that, although cholecystokinin may be involved in exploratory behaviour exhibited by rats in a novel environment (unhabituated rats), its role is negligible in rats subjected to a familiar environment (habituated rats). Furthermore, these results support the interpretation that cholecystokinin has a suppressant effect on locomotion elicited by phencyclidine and MK-801, and that this inhibitory action of cholecystokinin is mediated via the cholecystokininB receptor, since it can be eliminated by administration of cholecystokininB antagonists. It is suggested that the site of action of the cholecystokininB receptors involves mainly the cholecystokinin/glutamate projection from the cortex to the anterior nucleus accumbens and/or striatum. Finally, the present study provides two examples of endogenous release of a neuropeptide resulting in behavioural consequences.

Knowledge of and Attitudes about Alzheimer Disease Genetics: Report of a Pilot Survey and Two Focus Groups

OBJECTIVES

In preparation for the development of an educational intervention on Alzheimer disease (AD) genetics, we undertook a pilot survey of knowledge in this area and attitudes toward genetic testing for AD among individuals with a family history of AD.

METHODS

For the pilot study, we administered a 30-min questionnaire to 57 unaffected individuals from a genetic linkage study. For the focus groups, we interviewed two groups of subjects, ages 44-70 years, with a family history of AD, one of 10 Caucasians and the other of 6 African-Americans.

RESULTS

The pilot study showed that there was limited knowledge of genetics overall and AD genetics in particular, considerable concern about personal risk, and little knowledge of or interest in genetic testing for the disease. The focus groups reinforced and fleshed out these impressions and highlighted the importance of caregiving experience in the attitudes toward personal risk for AD.

CONCLUSIONS

These results underscore the value of genetics education for this and other complex diseases and suggest specific foci for educational interventions.

New insights into genetic aspects of Alzheimer's disease. Does genetic information make a difference in clinical practice?

Genetic testing sometimes offers definitive information for patients who have a family history of early-onset Alzheimer's disease that occurs before age 50 in a Mendelian pattern. However, for patients who are already symptomatic, especially those with sufficient symptoms to warrant a clinical diagnosis of Alzheimer's disease, genetic testing may not contribute a great deal of information beyond that already available from the clinical and family history. For prediction of disease onset, genetic testing can sometimes give a clear picture of disease risk, but each patient must carefully weigh the risks and benefits of having that information. For early-onset Alzheimer's disease occurring beyond age 50 or without a clear Mendelian pattern, genetic testing is unlikely to be informative. In patients who have a family history of late-onset Alzheimer's disease, while APOE's contribution to increased risk is indisputable, its potential use as a genetic test is very limited. Testing may be helpful as an adjunct to clinical diagnosis but does not obviate the need for a full workup for treatable causes. Thus, the benefit of testing may be marginal. No consensus has been reached as to the value of genetic testing for early detection of late-onset disease, but APOE testing might become important in the future if it helps to define the need for intervention or to select an optimal intervention. There is a broad consensus that APOE testing lacks sufficient predictive value to be suitable for predictive testing in asymptomatic persons.

Modulation of motor behaviour by NMDA- and cholecystokinin-antagonism

Motor behaviour relies on complex neurochemical interactions in the basal ganglia, in particular the striatum. Antagonistic influences in this region are exerted by afferent projections from, on the one hand, the ventral mesencephalon, utilizing dopamine as a transmitter, and, on the other hand, from the cerebral cortex, signalling by the excitatory amino acid glutamate. The activity in both these neuronal populations appears to be regulated by the neuropeptide cholecystokinin. This article concentrates on interactions between cholecystokinin and glutamate, summarizing some recent morphological, biochemical and behavioural findings. It is suggested that cholecystokinin, acting via the cholecystokininB receptor, potentiates the glutamatergic excitatory input to the striatum.

Genomic structure, expression pattern, and chromosomal localization of the human calsenilin gene: no association between an exonic polymorphism and Alzheimer's disease

Calsenilin is a recently-identified member of the neuronal calcium sensor family. Like other members of this family, it is found in the brain and binds calcium. Calsenilin was discovered by virtue of its interaction with both presenilin-1 and -2, proteins that are involved in the etiology of Alzheimer's disease. Because calsenilin may play a role in Alzheimer's disease and other disease with alterations in calcium homeostasis, we characterized the human gene. The gene, which we localized to chromosome 2, extends over a region of at least 74 kb and includes nine exons. Interestingly, the ninth exon of calsenilin contains a highly polymorphic CA repeat, adjacent to the stop codon. In a study of Alzheimer patients and their unaffected siblings, there was no evidence of association of AD with any calsenilin allele. This CA repeat will be useful for linkage and linkage disequilibrium studies to determine whether calsenilin variants contribute to risk in other diseases.

Family-based tests of association in the presence and absence of known linkage

Correlation among sibling marker genotypes may invalidate the results of family-based tests of association in the presence of linkage. We apply an empirical variance estimation method, which is implemented in the program package FBAT, on Caucasian families with asthma in the presence and absence of linkage and compare the results with those obtained using the TDT (TDTEX-PAIRS) on the same data sets. Our results indicate that both tests generally perform comparably in either setting.

The importance of watching our weights: how the choice of weights for non-independent sib pairs can dramatically alter results

Handling non-independent sib pairs in families with multiple affected sibs presents a problem in likelihood-based nonparametric linkage analyses. We contrast the more stable partial-likelihood solution in MAPMAKER/SIBS with the extremely variable partial-likelihood approach used in ASPEX, and the potential inflation of lods when the problem is ignored as in BETA.