Donna G. Crenshaw

A TOMM40 variable-length polymorphism predicts the age of late-onset Alzheimer's disease.

The ɛ4 allele of the apolipoprotein E (APOE) gene is currently the strongest and most highly replicated genetic factor for risk and age of onset of late-onset Alzheimers disease (LOAD). Using phylogenetic analysis, we have identified a polymorphic poly-T variant, rs10524523, in the translocase of outer mitochondrial membrane 40 homolog (TOMM40) gene that provides greatly increased precision in the estimation of age of LOAD onset for APOE ɛ3 carriers. In two independent clinical cohorts, longer lengths of rs10524523 are associated with a higher risk for LOAD. For APOE ɛ3/4 patients who developed LOAD after 60 years of age, individuals with long poly-T repeats linked to APOE ɛ3 develop LOAD on an average of 7 years earlier than individuals with shorter poly-T repeats linked to APOE ɛ3 (70.5±1.2 years versus 77.6±2.1 years, P=0.02, n=34). Independent mutation events at rs10524523 that occurred during Caucasian evolution have given rise to multiple categories of poly-T length variants at this locus. On replication, these results will have clinical utility for predictive risk estimates for LOAD and for enabling clinical disease prevention studies. In addition, these results show the effective use of a phylogenetic approach for analysis of haplotypes of polymorphisms, including structural polymorphisms, which contribute to complex diseases.

The mitotic peptidyl-prolyl isomerase, Pin1, interacts with Cdc25 and Plx1.

The cis/trans peptidyl‐prolyl isomerase, Pin1, is a regulator of mitosis that is well conserved from yeast to man. Here we demonstrate that depletion of Pin1‐binding proteins from Xenopus egg extracts results in hyperphosphorylation and inactivation of the key mitotic regulator, Cdc2/cyclin B. We show biochemically that this phenotype is a consequence of Pin1 interaction with critical upstream regulators of Cdc2/cyclin B, including the Cdc2‐directed phosphatase, Cdc25, and its known regulator, Plx1. Although Pin1 could interact with Plx1 during interphase and mitosis, only the phosphorylated, mitotically active form of Cdc25 was able to bind Pin1, an event we have recapitulated using in vitro phosphorylated Cdc25. Taken together, these data suggest that Pin1 may modulate cell cycle control through interaction with Cdc25 and its activator, Plx1.

Genetic variation at a single locus and age of onset for Alzheimer's disease

This perspective article provides an opportunity to explain a new genetic finding for late‐onset Alzheimers 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 Alzheimers 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.

Using genetics to enable studies on the prevention of Alzheimer's disease.

Curing Alzheimers disease (AD) remains an elusive goal; indeed, it may even prove to be impossible, given the nature of the disease. Although modulating disease progression is an attractive target and will alleviate the burden of the most severe stages, this strategy will not reduce the prevalence of the disease itself. Preventing or (as described in this article) delaying the onset of cognitive impairment and AD will provide the greatest benefit to individuals and society by pushing the onset of disease into the later years of life. Because of the high variability in the age of onset of the disease, AD prevention studies that do not stratify participants by age‐dependent disease risk will be operationally challenging, being large in size and of long duration. We present a composite genetic biomarker to stratify disease risk so as to facilitate clinical studies in high‐risk populations. In addition, we discuss the rationale for the use of pioglitazone to delay the onset of AD in individuals at high risk.

TOMM40 and APOE: Requirements for replication studies of association with age of disease onset and enrichment of a clinical trial

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 Alzheimers 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.

New applications of disease genetics and pharmacogenetics to drug development.

TOMMORROW is a Phase III delay of onset clinical trial to determine whether low doses of pioglitazone, a molecule that induces mitochondrial doubling, delays the onset of MCI-AD in normal subjects treated with low dose compared to placebo. BOLD imaging studies in rodents and man were used to find the dose that increases oxygen consumption at central regions of the brain in higher proportion than activation of large corticol regions. The trial is made practical by the use of a pharmacogenetic algorithm based on TOMM40 and APOE genotypes and age to identify normal subjects at high risk of MCI-AD between the ages of 65-83 years within a five year follow-up period.

The cis-regulatory effect of an Alzheimer’s disease-associated poly-T locus on expression of TOMM40 and apolipoprotein E genes

We investigated the genomic region spanning the Translocase of the Outer Mitochondrial Membrane 40‐kD (TOMM40) and Apolipoprotein E (APOE) genes, that has been associated with the risk and age of onset of late‐onset Alzheimers disease (LOAD) to determine whether a highly polymorphic, intronic poly‐T within this region (rs10524523; hereafter, 523) affects expression of the APOE and TOMM40 genes. Alleles of this locus are classified as S, short; L, long; and VL, very long based on the number of T residues.

Effects of Low Doses of Pioglitazone on Resting-State Functional Connectivity in Conscious Rat Brain

Pioglitazone (PIO) is a peroxisome proliferator-activated receptor-γ (PPARγ) agonist in clinical use for treatment of type 2 diabetes (T2DM). Accumulating evidence suggests PPARγ agonists may be useful for treating or delaying the onset of Alzheimer’s disease (AD), possibly via actions on mitochondria, and that dose strengths lower than those clinically used for T2DM may be efficacious. Our major objective was to determine if low doses of pioglitazone, administered orally, impacted brain activity. We measured blood-oxygenation-level dependent (BOLD) low-frequency fluctuations in conscious rats to map changes in brain resting-state functional connectivity due to daily, oral dosing with low-dose PIO. The connectivity in two neural circuits exhibited significant changes compared with vehicle after two days of treatment with PIO at 0.08 mg/kg/day. After 7 days of treatment with a range of PIO dose-strengths, connections between 17 pairs of brain regions were significantly affected. Functional connectivity with the CA1 region of the hippocampus, a region that is involved in memory and is affected early in the progression of AD, was specifically investigated in a seed-based analysis. This approach revealed that the spatial pattern of CA1 connectivity was consistent among all dose groups at baseline, prior to treatment with PIO, and in the control group imaged on day 7. Compared to baseline and controls, increased connectivity to CA1 was observed regionally in the hypothalamus and ventral thalamus in all PIO-treated groups, but was least pronounced in the group treated with the highest dose of PIO. These data support our hypothesis that PIO modulates neuronal and/or cerebrovascular function at dose strengths significantly lower than those used to treat T2DM and therefore may be a useful therapy for neurodegenerative diseases including AD.

The Importance of Being Connected

In the 17 years since the original report linking the 4 allele of the apolipoprotein E (APOE) gene [1] with late-onset Alzheimer’s disease (LOAD), considerable effort has been expended to elucidate the role that APOE plays in LOAD risk and age of disease onset. LOAD is a genetically complex and heterogeneous disorder. The disease has a strong heritability that is estimated to reach nearly 80% [2], yet only a few genes that account for a proportion of the observed genetic variability have been definitively associated with the disease [3]. The only firmly established genetic risk factor for sporadic AD, and the risk factor with the largest effect size, is the 4 allele of APOE [4]. Carriage of an APOE 4 allele significantly increases the lifetime risk for AD, with the level of risk increasing as the 4 allele dose increases [4, 5], and is associated with lower age of disease onset [4, 6–9]. The APOE gene occurs in an extended linkage region on chromosome 19 that provides an extraordinary genome wide association signal with LOAD. This association signal is generally attributed to the 4 allele of APOE, but other polymorphisms in adjacent genes and the APOE promoter may also contribute to disease pathogenesis. In this commentary, we consider the findings of Lescai et al. [10] in the context of an extensive phylogenetic analysis of the TOMM40-APOE region recently reported by our group [11, 12]. In this issue, Lescai and colleagues identify a haplotype, comprised of a specific allele of an APOE

Pipeline Pharmacogenetics: A Novel Approach to Integrating Pharmacogenetics into Drug Development

There has been a decline in the number of new drugs registered over the past decade and regulatory concerns for safety as well as payer concerns for efficacy have focused attention on stratified medicine. Integration of pharmacogenetics into the drug development pipeline will contribute to the development of new stratified drugs. We describe here the concept of pipeline pharmacogenetics and its application throughout the phases of drug discovery. Pipeline pharmacogenetics enables the evaluation of the genetic contribution to safety potentially lowering barriers to registration as well as providing rationale for efficacy and enabling co-development of genetic in vitro diagnostics.