Clinical and neurobiological correlates of D10S1423 genotype in Alzheimer's disease

D10S1423 identifies a susceptibility locus for Alzheimer's disease (AD7) in a prospective, longitudinal, double-blind study of asymptomatic individuals: results at 14 years

Typical forms of Alzheimer's disease (AD) appear to be influenced by multiple susceptibility loci. This report describes the prospective, longitudinal, double-blind assessment of the age-specific risk of AD encountered by 325 asymptomatic first-degree relatives of AD probands who carried the D10S1423 (AD7) 234 bp allele, the APOE E4 allele, or both, after 14 years of systematic follow-up. A total of 30 incident cases of AD were detected during the first 3752 subject-years of surveillance. The effects of carrying either or both of the D10S1423 234 bp and APOE E4 alleles on the age-specific risk of developing AD were determined using Kaplan-Meier survival analysis. The risk of developing AD was the greatest for individuals who carried both alleles (Mantel-Cox statistic = 16.46, df = 3, P = 0.0009; Breslow statistic = 13.38, df = 3, P = 0.004). Cox proportional hazards models were developed to estimate the risk ratios for each genotype, controlling for the potential effects of age at recruitment, sex, and years of education. Only individuals who carried both risk alleles exhibited a risk ratio that differed significantly from 1 (risk ratio = 7.5, P = 0.002, 95% CI = 2.1-27.0). Neither age at recruitment, sex, nor years of education made significant contributions to the model, although women tended to be at greater risk (P = 0.06). Recent evidence that D10S1423 resides within open reading frame C10orf112, whose predicted product resembles a low-density lipoprotein receptor, suggests a molecular mechanism for this gene-gene interaction.

Predicted gene sequence C10orf112 is transcribed, exhibits tissue-specific expression, and may correspond to AD7

Case-control and prospective longitudinal studies have revealed an interaction of the anonymous D10S1423 234 bp allele with the APOE4 allele in determining the age-specific risk of Alzheimer's disease (AD). The D10S1423 polymorphism resides within intron 10 of open reading frame C10orf112, whose predicted product resembles a low-density lipoprotein receptor (NCBI Build 35.1). These observations suggest that the D10S1423 234 bp allele may be in linkage disequilibrium with a C10orf112 gene variant whose product interacts with the apoE4 lipoprotein. Our initial exploration of this hypothesis focused on validating the C10orf112 gene model. RT-PCR amplification from human hippocampal mRNA confirmed that 34 of the predicted 39 exons of C10orf112 were expressed in this brain region. Northern blots revealed 1.2 kb and 3.2 kb mRNA species that hybridize to a cDNA probe consisting of contiguous exons 23-26. Expression of these C10orf112 mRNA species was limited to a subset of brain regions and heart tissue.

Huperzine A Reverses Cholinergic and Monoaminergic Dysfunction Induced by Bilateral Nucleus Basalis Magnocellularis Injection of β-Amyloid Peptide (1–40) in Rats

(1) Huperzine A, a promising therapeutic agent for Alzheimer's disease (AD), was tested for its effects on cholinergic and monoaminergic dysfunction induced by injecting beta-amyloid peptide-(1-40) into nucleus basalis magnocellularis of the rat. (2) Bilateral injection of 10 microg beta-amyloid peptide-(1-40) into nucleus basalis magnocellularis produced local deposits of amyloid plaque and functional abnormalities detected by microdialysis. In medial prefrontal cortex, reductions in the basal levels and stimulated release of acetylcholine, dopamine, norepinephrine, and 5-hydroxytryptamine were observed. However, oral huperzine A (0.18 mg/kg, once daily for 21 consecutive days) markedly reduced morphologic abnormalities at the injection site in rats infused with beta-amyloid peptide-(1-40). Likewise, this treatment ameliorated the beta-amyloid peptide-(1-40)-induced deficits in extracellular acetylcholine, dopamine, and norepinephrine (though not 5-hydroxytryptamine) in medial prefrontal cortex, and lessened the reduction in nicotine or methoctramine-stimulated release of acetylcholine and K(+)-evoked releases of acetylcholine and dopamine. (3) The present results provide the first direct evidence that huperzine A acts to oppose neurotoxic effects of beta-amyloid peptide on cholinergic, dopaminergic, and noradrenergic systems of the rat forebrain.

Genome survey for loci that influence successful aging: results at 10-cM resolution

OBJECTIVE

A systematic genome survey was initiated to identify loci that affect the likelihood of reaching age 90 with preserved cognition (successful aging).

METHODS

The genome survey was conducted at 10-cM resolution for simple sequence tandem repeat polymorphisms (SSTRPs) that identify genes for Successful AGing (SAG loci) by virtue of linkage disequilibrium. Efficiency was enhanced by genotyping pools of DNA from 100 cognitively intact elders and 100 young (18-25 years) adults. The comparison groups included equal numbers of white men and women of similar ethnicity that were recruited from the southwestern Pennsylvania region.

RESULTS

Our genome survey identified nine SAG candidate loci that may influence the likelihood of reaching age 90 or more with preserved cognition. Two of the autosomal SAG loci revealed stronger allelic associations with successful aging in men than women (D1S1728, D8S264) and two were located on sex chromosomes (DXS9902, DYS390). DXS9902 resides within a predicted gene, whereas six of the SAG loci are located within regions previously reported to show linkage to other phenotypes.

CONCLUSIONS

The results of our study suggest that loci with differential effects on the successful aging of men and women may be common. The majority of the SAG candidate loci detected in this study overlap with regions previously reported to show linkage to susceptibility genes for cardiovascular disorders, psychiatric disorders, and the accumulation of tissue damage resulting from oxidative stress.

D2S2944 identifies a likely susceptibility locus for recurrent, early-onset, major depression in women

Recurrent, early-onset, major depressive disorder (RE-MDD) is a strongly familial condition whose malignant effects have a significant negative impact on the health and longevity of patients and their family members. Sixteen of the 19 candidate susceptibility loci identified by a recent genome survey revealed allelic associations with RE-MDD in men or women, but not in both sexes. The association of D2S2944 alleles and genotypes with RE-MDD and related disorders was evaluated using a case-control study design employing 100 adults with RE-MDD and 100 adult controls who had no personal or family history of mental disorders. The results of the case-control study were subsequently evaluated in a sample of 81 families ascertained through probands with RE-MDD using the transmission/disequilibrium test. The frequency of the D2S2944 124-bp allele among women with RE-MDD was approximately three times that for female controls (P = 0.0003). Women who carried the D2S2944 124-bp allele revealed a significantly elevated risk of developing RE-MDD, as indicated by an odds ratio of 4.5 compared to female controls (P<0.001). In contrast, men with RE-MDD did not have an increased frequency of this allele compared to male controls, and men who were carriers did not exhibit an increased risk of developing RE-MDD or related disorders. Our findings also suggest that the D2S2944 124-bp allele increases the risk of alcohol and other substance use disorders among women with RE-MDD. The transmission/disequilibrium test provided confirmatory evidence of these sex-specific findings within families. The results of this study confirm the existence of sex-specific susceptibility loci for RE-MDD, and suggest that there may be important differences in the molecular pathophysiology of RE-MDD in men and women. Alternatively, our findings may reflect the existence of sex-specific differences in the molecular mechanisms that determine resilience to endogenous or environmental depressogenic stimuli. The identification and characterization of the D2S2944 susceptibility locus for RE-MDD and related substance use disorders is likely to provide important new insights into the clinical biology, treatment, and prevention of these disorders.

Genome survey for susceptibility loci for recurrent, early-onset major depression: results at 10cM resolution

Recurrent (two or more episodes), early-onset (first episode at < or = 25 years) major depressive disorder (RE-MDD) is a strongly familial condition (lambda(first-degree relatives) = 8) whose malignant effects have a significant negative impact on the health and longevity of patients and their family members. The goal of this study was to identify candidate susceptibility loci that influence the development of RE-MDD. We completed a systematic survey of the human genome, conducted at an average resolution of 10 cM, for the identification of simple sequence tandem repeat polymorphisms (SSTRPs) that target susceptibility genes for RE-MDD by virtue of linkage disequilibrium. The efficiency of our association study was enhanced by genotyping pools of DNA from 100 adults with RE-MDD and 100 adult controls who had no personal or family history of mental disorders. Both groups included equal numbers of Caucasian men and women and were matched as closely as possible for age and ethnicity. Allelic associations with RE-MDD were observed for 19 of the 387 SSTRPs in the CHLC Human Screening Set/Weber Version 9. Sixteen of the 19 candidate susceptibility loci revealed significant allelic associations with RE-MDD in men (n = 7) or women (n = 9), but not in both sexes. Evidence for both risk and protective alleles was detected. Two of the candidate susceptibility loci reside within several Mb of loci previously reported-megabases to be linked to "comorbid alcoholism and depression" in families of individuals with alcoholism and to a broadly defined affected phenotype that included recurrent major depression in the families of patients with bipolar disorder. Although it has been suggested that the genes that influence risk for MDD in the two sexes may not be entirely the same, the results of our study suggest that sex specificity of susceptibility loci for RE-MDD may be the rule rather than the exception. The observed preponderance of sex-specific susceptibility loci for RE-MDD suggests that there may be important differences in the molecular pathophysiology of RE-MDD in men and women. Alternatively, our findings may reflect the existence of sex-specific differences in the molecular mechanisms that determine resilience to endogenous or environmental depressogenic stimuli.

D10S1423 identifies a susceptibility locus for Alzheimer's disease in a prospective, longitudinal, double-blind study of asymptomatic individuals

Typical, later-onset forms of Alzheimer's disease (AD) appear to be influenced by multiple susceptibility loci, combinations of which contribute to the development of this disorder. We previously reported the results of a systematic survey of the human genome for the identification of highly informative DNA polymorphisms (SSTRPs) that target new AD risk genes. In addition to the APOE locus, our survey detected five new candidate susceptibility loci for AD, including D10S1423. An association of the D10S1423 234-bp allele with AD has been reported in three independent samples of AD cases and controls (Boston, Pittsburgh, Bonn). Data from our case-control studies suggest a strong synergistic interaction between the D10S1423 234-bp and APOE E4 risk alleles (234-bp carrier: OR = 2.5, 95% CI = 1.4--4.5; E4 carrier: OR = 8.3, 95% CI = 4.3--15.8; both alleles: OR = 23.1, 95% CI = 5.3--99.5). This report describes the prospective, longitudinal, double-blind assessment of the age-specific risk of AD encountered by 325 asymptomatic first-degree relatives of AD probands who carried the D10S1423 234-bp allele, the APOE E4 allele, or both, after 11.5 years of systematic follow-up. A total of 18 incident cases of AD were detected during the first 3379 subject-years of this longitudinal study. The effects of carrying either or both of the D10S1423 234-bp and APOE E4 alleles on the age-specific risk of developing AD were determined using Kaplan-Meier survival analysis. The age-specific risk of developing AD was the greatest for individuals who carried both alleles (Mantel--Cox statistic = 20.12, df = 3, P = 0.0002; Breslow statistic = 13.36, df = 3, P = 0.004). Cox proportional hazards models were developed to estimate the risk ratios for each genotype, controlling for the potential effects of age at recruitment, sex, and years of education. In the resulting best fitting model, only individuals who carried both risk alleles exhibited a risk ratio that differed significantly from 1 (risk ratio = 16.2, P = 0.008, 95% CI = 2.1--128.3). After controlling for these genotypes, female gender was also significantly associated with increased risk of developing AD (risk ratio = 5.1, P = 0.02, 95% CI = 1.2--21.1). Neither age at recruitment nor years of education made significant contributions to the model.

Allelic association between the D10S1423 marker and Alzheimer's disease in a German population

Recently a full genome survey detected an allelic association between Alzheimer's disease (AD) and the D10S1423 marker on chromosome 10p12-14 (40 cM from the telomere). In this study we examined the D10S1423 marker in an ethnically homogeneous German population of 80 AD patients and two groups of controls, 168 healthy subjects and 149 depressed patients. The 234-bp allele of the D10S1423 marker showed a significant association with AD (P = 0.033). In conclusion, our results support that the D10S1423 marker is associated with an increased AD risk and provides further evidence for an AD susceptibility locus on chromosome 10.

Do susceptibility loci contribute to the expression of more than one mental disorder? A view from the genetics of Alzheimer's disease

The susceptibility of developing most major psychiatric disorders is determined in part by contributions from risk alleles at multiple genetic loci. The central aim of this article is to highlight evidence from studies of neurodegenerative disorders suggesting that some of these alleles are shared by more than one psychiatric disorder, and to explore mechanisms that may underly these pleiotropic effects. The identification of constellations of susceptibility alleles associated with particular mental disorders will provide opportunities for new insights into the molecular and cellular pathophysiology of these disorders, and will have a major impact on psychiatric research and clinical care. This approach to reducing the variance in etiopathogenesis is also likely to be important for achieving the optimal use of available treatments (maximizing effectiveness and minimizing side effects), and for the discovery of novel medications or other interventions.