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ABSTRACT: A number of recent studies have not replicated the association of the translocase of the outer mitochondrial membrane pore subunit (TOMM40) rs10524523 polymorphism, which is in linkage disequilibrium with apolipoprotein E (APOE), with age of onset of Alzheimer's disease (AD). This perspective describes the differences between these later studies and the original experiments. We highlight the necessity for using standardized and informative assessment tools and processes when determining the age of development of AD or AD symptoms, and also stress that this clinical phenotype is best measured reliably in prospective studies during which subjects are monitored over time. This is true when assessing potential biomarkers for age of onset and when assessing the therapeutic potential of medicines that may delay the onset or progression of this disease.
Alzheimer's & dementia: the journal of the Alzheimer's Association 01/2013; · 5.90 Impact Factor
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ABSTRACT: TOMM40 (translocase of the outer mitochondrial membrane pore subunit) is in linkage disequilibrium with apolipoprotein E (APOE). APOE e4 is linked to long (L; 21-29 T residues) poly-T variants within intron 6 of TOMM40, whereas APOE e3 can be associated with either a short (S; <21 T residues) or very long (VL; >29 T residues) variant. To assess the possible contribution of TOMM40 to Alzheimer's disease onset, we compared the effects of TOMM40 and APOE genotype on preclinical longitudinal memory decline.
An APOE e4-enriched cohort of 639 cognitively normal individuals aged 21 to 97 years with known TOMM40 genotype underwent longitudinal neuropsychological testing every 2 years. We estimated the longitudinal effect of age on memory using statistical models that simultaneously modeled cross-sectional and longitudinal effects of age on the Auditory Verbal Learning Test Long-Term Memory score by APOE, TOMM40, and the interaction between the two.
There were significant effects overall for both TOMM40 (linear effect, P = .04; quadratic effect, P = .03) and APOE (linear effect, P = .06; quadratic effect, P = .008), with no significant interaction (P = .63). In a piecewise model, there was a significant TOMM40 effect before age 60 years (P = .009), characterized by flattened test-retest improvement (VL/VL subgroup only) but no significant APOE effect, and a significant APOE effect after age 60 years (P = .006), characterized by accelerated memory decline (e4 carriers) but no significant TOMM40 effect.
Both TOMM40 and APOE significantly influence age-related memory performance, but they appear to do so independently of each other.
Alzheimer's & dementia: the journal of the Alzheimer's Association 11/2012; 8(6):490-5. · 5.90 Impact Factor
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ABSTRACT: A highly polymorphic T homopolymer was recently found to be associated with late-onset Alzheimer's disease risk and age of onset.
To explore the effects of the polymorphic polyT tract (rs10524523, referred as '523') on cognitive performance in cognitively healthy elderly individuals.
One hundred eighty-one participants were recruited from local independent-living retirement communities. Informed consent was obtained, and participants completed demographic questionnaires, a conventional paper-and-pencil neuropsychological battery, and the computerized Cambridge Neuropsychological Test Automated Battery (CANTAB). Saliva samples were collected for determination of the TOMM40 '523' (S, L, VL) and the apolipoprotein E (APOE) (ɛ2, 3, 4) genotypes. From the initial sample of 181 individuals, 127 were eligible for the association analysis. Participants were divided into three groups based on '523' genotypes (S/S, S/L-S/VL, and L/L-L/VL-VL/VL). Generalized linear models were used to evaluate the association between the '523' genotypes and neuropsychological test performance. Analyses were adjusted for age, sex, education, depression, and APOE ɛ4 status. A planned subanalysis was undertaken to evaluate the association between '523' genotypes and test performance in a sample restricted to APOE ɛ3 homozygotes.
The S homozygotes performed better, although not significantly, than the S/L-S/VL and the VL/L-L/VL-VL/VL genotype groups on measures associated with memory (CANTAB Paired Associates Learning, Verbal Recognition Memory free recall) and executive function (CANTAB measures of Intra-Extra Dimensional Set Shift). Follow-up analysis of APOE ɛ3 homozygotes only showed that the S/S group performed significantly better than the S/VL group on measures of episodic memory (CANTAB Paired Associates Learning and Verbal Recognition Memory free recall), attention (CANTAB Rapid Visual Information Processing latency), and executive function (Digit Symbol Substitution). The S/S group performed marginally better than the VL/VL group on Intra-Extra Dimensional Set Shift. None of the associations remained significant after applying a Bonferroni correction for multiple testing.
Results suggest important APOE-independent associations between the TOMM40 '523' polymorphism and specific cognitive domains of memory and executive control that are preferentially affected in early-stage Alzheimer's disease.
Alzheimer's & dementia: the journal of the Alzheimer's Association 08/2012; 8(5):381-8. · 5.90 Impact Factor
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Colton Linnertz,
Ann M Saunders, Michael W Lutz,
Donna M Crenshaw,
Iris Grossman,
Daniel K Burns,
Keith E Whitfield,
Michael A Hauser,
Jeanette J McCarthy,
Megan Ulmer,
Rand Allingham,
Kathleen A Welsh-Bohmer,
Allen D Roses,
Ornit Chiba-Falek
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ABSTRACT: We previously discovered that a polymorphic, deoxythymidine-homopolymer (poly-T, rs10524523) in intron 6 of the TOMM40 gene is associated with age-of-onset of Alzheimer's disease and with cognitive performance in elderly. Three allele groups were defined for rs10524523, hereafter '523', based on the number of 'T'-residues: 'Short' (S, T≤19), 'Long' (L, 20≤T≤29) and 'Very Long' (VL, T≥30). Homopolymers, particularly long homopolymers like '523', are difficult to genotype because 'slippage' occurs during PCR-amplification. We initially genotyped this locus by PCR-amplification followed by Sanger-sequencing. However, we recognized the need to develop a higher-throughput genotyping method that is also accurate and reliable. Here we describe a new '523' genotyping assay that is simple and inexpensive to perform in a standard molecular genetics laboratory. The assay is based on the detection of differences in PCR-fragment length using capillary electrophoresis. We discuss technical problems, solutions, and the steps taken for validation. We employed the novel assay to investigate the '523' allele frequencies in different ethnicities. Whites and Hispanics have similar frequencies of S/L/VL alleles (0.45/0.11/0.44 and 0.43/0.09/0.48, respectively). In African-Americans, the frequency of the L-allele (0.10) is similar to Whites and Hispanics; however, the S-allele is more prevalent (0.65) and the VL-allele is concomitantly less frequent (0.25). The allele frequencies determined using the new methodology are compared to previous reports for Ghanaian, Japanese, Korean and Han Chinese cohorts. Finally, we studied the linkage pattern between TOMM40-'523' and APOE alleles. In Whites and Hispanics, consistent with previous reports, the L is primarily linked to ε4, while the majority of the VL and S are linked to ε3. Interestingly, in African-Americans, Ghanaians and Japanese, there is an increased frequency of the '523'S-APOEε4 haplotype. These data may be used as references for '523' allele and '523'-APOE haplotype frequencies in diverse populations for the design of research studies and clinical trials.
PLoS ONE 01/2012; 7(2):e30994. · 4.09 Impact Factor
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ABSTRACT: Neurofilament light (NFL) proteins in cerebrospinal fluid (CSF) are a marker of neuronal damage, especially subcortical axonal injury and white matter disease. Subjects with Alzheimer's disease (AD) have shown elevated levels of CSF NFL as compared to controls. However, the presence of the APOE ε4 allele, an established risk factor for AD, was not found to associate with higher CSF NFL concentrations. We examined whether TOMM40 variants, which have been reported to influence age of onset of AD and are in linkage disequilibrium with APOE, have an effect on CSF NFL levels, in 47 healthy, cognitively intact individuals with or without APOE ε4. Our results show that the presence of APOE ε4 alone does not affect CSF NFL levels significantly; however APOE and TOMM40 appear to interact. Subjects with APOE ε4 have higher CSF NFL levels than non-ε4 carriers, only when they do not carry a short poly-T variant of TOMM40, which is associated with later age of onset of AD, and may act as protective against the dose effect of ε4.
Experimental gerontology 10/2011; 47(5):347-52. · 3.34 Impact Factor
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Journal of clinical psychopharmacology 08/2011; 31(4):544-6. · 5.09 Impact Factor
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ABSTRACT: Abnormalities of the hypothalamic-pituitary-adrenal (HPA) axis have been reported in subjects with Alzheimer's disease (AD) and may include increased cerebrospinal fluid (CSF) cortisol concentrations. Moreover, presence of the APOE ɛ4 allele, which is an established risk factor for the development of AD, has been shown to associate with higher CSF cortisol levels, especially in AD sufferers. In this study, we examined whether TOMM40 variants, which have been reported to influence age of onset of AD, also had an effect on CSF cortisol levels, in healthy, cognitively intact individuals with or without APOE ɛ4. In our results, the increase in CSF cortisol associated with the presence of the APOE ɛ4 allele was only detected when a short TOMM40 poly-T variant, shown to associate with later age of onset of AD in ɛ4 carriers, was not present. These results are consistent with previous reports (e.g., Roses et al., 2009) suggesting that TOMM40 poly-T variants influence the effects of APOE alleles.
Psychoneuroendocrinology 07/2011; 37(3):366-71. · 5.81 Impact Factor
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Sterling C Johnson,
Asenath La Rue,
Bruce P Hermann,
Guofan Xu,
Rebecca L Koscik,
Erin M Jonaitis,
Barbara B Bendlin,
Kirk J Hogan,
Allen D Roses,
Ann M Saunders, Michael W Lutz,
Sanjay Asthana,
Robert C Green,
Mark A Sager
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ABSTRACT: Apolipoprotein E (APOE) genotypes are associated with variable risk of developing late-onset Alzheimer's disease (LOAD), with APOE epsilon 4 (APOE ε4) having higher risk. A variable poly-T length polymorphism at rs10524523, within intron 6 of the translocase of the outer mitochondrial membrane (TOMM40) gene, has been shown to influence age of onset in LOAD, with very long (VL) poly-T length associated with earlier disease onset, and short poly-T length associated with later onset. In this study, we tested the hypothesis that brain and cognitive changes suggestive of presymptomatic LOAD may be associated with this TOMM40 polymorphism.
Among healthy APOE ε3 homozygous adults (N = 117; mean age, 55 years), we compared those who were homozygous for VL/VL (n = 35) TOMM40 poly-T lengths (who were presumably at higher risk) with those homozygous for short (S/S; n = 38) poly-T lengths, as well as those with heterozygous (S/VL; n = 44) poly-T length polymorphisms, on measures of learning and memory and on structural brain imaging.
The VL/VL group showed lower performance than the S/S TOMM40 group on primacy retrieval from a verbal list learning task, a finding which is also seen in early Alzheimer's disease. A dose-dependent increase in the VL TOMM40 polymorphism (from no VL alleles, to S/VL heterozygous, to VL/VL homozygous) was associated with decreasing gray matter volume in the ventral posterior cingulate and medial ventral precuneus, a region of the brain affected early in LOAD.
These findings among APOE ε3/ε3 late middle-aged adults suggest that a subgroup with VL TOMM40 poly-T lengths may be experiencing incipient LOAD-related cognitive and brain changes.
Alzheimer's & dementia: the journal of the Alzheimer's Association 07/2011; 7(4):456-65. · 5.90 Impact Factor
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Journal of Alzheimer's disease: JAD 01/2011; 24(2):247-51. · 3.74 Impact Factor
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ABSTRACT: Alzheimer's disease (AD) presents one of the leading healthcare challenges of the 21st century, with a projected worldwide prevalence of >107 million cases by 2025. While biomarkers have been identified, which may correlate with disease progression or subtype for the purpose of disease monitoring or differential diagnosis, a biomarker for reliable prediction of late onset disease risk has not been available until now. This deficiency in reliable predictive biomarkers, coupled with the devastating nature of the disease, places AD at a high priority for focus by predictive, preventive and personalized medicine. Recent data, discovered using phylogenetic analysis, suggest that a variable length poly-T sequence polymorphism in the TOMM40 gene, adjacent to the APOE gene, is predictive of risk of AD age-of-onset when coupled with a subject's current age. This finding offers hope for reliable assignment of disease risk within a 5-7 year window, and is expected to guide enrichment of clinical trials in order to speed development of preventative medicines.
EPMA Journal, The 06/2010; 1(2):293-303.
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ABSTRACT: This perspective article provides an opportunity to explain a new genetic finding for late-onset Alzheimer's disease (LOAD). It is specifically written for physicians and scientists who are interested in LOAD, but it may be relevant to those interested in identifying susceptibility variants for other complex diseases. The significant finding discussed here is that a variable-length, deoxythymidine homopolymer (poly-T) within intron 6 of the TOMM40 gene is associated with the age of onset of LOAD [Roses AD, Lutz MW, Amrine-Madsen H, Saunders AM, Crenshaw DG, Sundseth SS, et al. A TOMM40 variable-length polymorphism predicts the age of late-onset Alzheimer's disease. Pharmacogenomics J 2009 December 22;[Epublication ahead of print]. This result was obtained with a phylogenetic study of the genetic polymorphisms that reside within the linkage disequilibrium (LD) block that contains the TOMM40, APOE, and APOC1 genes from patients with LOAD and age-matched subjects without disease. Although the data will have diagnostic, prognostic, and therapeutic strategy implications, this perspective is meant to place the inheritance pattern for this "complex" human disease into context, and to highlight the potential utility of applying phylogenetic tools to the study of the genetics of complex diseases.
Alzheimer's & dementia: the journal of the Alzheimer's Association 03/2010; 6(2):125-31. · 5.90 Impact Factor
