Utility of Polygenic Risk Scoring to Predict Cognitive Impairment as Measured by Preclinical Alzheimer Cognitive Composite Score.

Background: The utility of Polygenic Risk Scores (PRS) is gaining increasing attention for generating an individual genetic risk profile to predict subsequent likelihood of future onset of Alzheimer's disease (AD), especially those carry two copies of the APOE E3 allele, currently considered at neutral risk in all populations studied. Objectives: To access the performance of PRS in predicting individuals whilst pre-symptomatic or with mild cognitive impairment who are at greatest risk of progression of cognitive impairment due to Alzheimer's Disease from the Alzheimer's Disease Neuroimaging Initiative (ADNI) as measured by the Preclinical Alzheimer Cognitive Composite (PACC) score profile. Design: A longitudinal analysis of data from the ADNI study conducted across over 50 sites in the US and Canada. Setting: Multi-centre genetics study. Participants: 594 subjects either APOE E3 homozygotes or APOE E3/E4 heterozygotes who upon entry to the study were diagnosed as cognitively normal or with mild cognitive impairment. Measurements: Use of genotyping and/or whole genome sequencing data to calculate polygenic risk scores and assess its ability to predict subsequent cognitive decline as measured by PACC over 5 years. Results: Assessing both cognitively normal and mild cognitive impaired subjects using a PRS threshold of greater than 0.6, the high genetic risk participant group declined more than the low risk group over 5 years as measured by PACC score (PACC score reduced by time). Conclusions: Our findings have shown that polygenic risk score provides a promising tool to identify those with higher risk to decline over 5 years regardless of their APOE alleles according to modified PACC profile, especially its ability to identify APOE3/E3 cognitively normal individuals who are at most risk for early cognitive decline. This genotype accounts for approximately 60% of the general population and 35% of the AD population but currently would not be considered at higher risk without access to expensive or invasive biomarker testing.

Polygenic Risk Scoring is an Effective Approach to Predict Those Individuals Most Likely to Decline Cognitively Due to Alzheimer's Disease.

BACKGROUND: There is a clear need for simple and effective tests to identify individuals who are most likely to develop Alzheimer's Disease (AD) both for the purposes of clinical trial recruitment but also for improved management of patients who may be experiencing early pre-clinical symptoms or who have clinical concerns. OBJECTIVES: To predict individuals at greatest risk of progression of cognitive impairment due to Alzheimer's Disease in individuals from the Alzheimer's Disease Neuroimaging Initiative (ADNI) using a polygenic risk scoring algorithm. To compare the performance of a PRS algorithm in predicting cognitive decline against that of using the pTau/Aß1-42 ratio CSF biomarker profile. DESIGN: A longitudinal analysis of data from the Alzheimer's Disease Neuroimaging Initiative study conducted across over 50 sites in the US and Canada. SETTING: Multi-center genetics study. PARTICPANTS: 515 subjects who upon entry to the study were diagnosed as cognitively normal or with mild cognitive impairment. MEASUREMENTS: Use of genotyping and/or whole genome sequencing data to calculate polygenic risk scores and assess ability to predict subsequent cognitive decline as measured by CDR-SB and ADAS-Cog13 over 4 years. RESULTS: The overall performance for predicting those individuals who would decline by at least 15 ADAS-Cog13 points from a baseline mild cognitive impairment in 4 years was 72.8% (CI:67.9-77.7) AUC increasing to 79.1% (CI: 75.6-82.6) when also including cognitively normal participants. Assessing mild cognitive impaired subjects only and using a threshold of greater than 0.6, the high genetic risk participant group declined, on average, by 1.4 points (CDR-SB) more than the low risk group over 4 years. The performance of the PRS algorithm tested was similar to that of the pTau/Aß1-42 ratio CSF biomarker profile in predicting cognitive decline. CONCLUSION: Calculating polygenic risk scores offers a simple and effective way, using DNA extracted from a simple mouth swab, to select mild cognitively impaired patients who are most likely to decline cognitively over the next four years.

Methacholine challenge in pre-school children--which outcome measure?

The aim of our study was to evaluate the utility of interrupter resistance (R(int)), transcutaneous oximetry and auscultation as outcome measures for a recently suggested tripling-dose methacholine (Mch) challenge in pre-school children. We studied 57 children aged 3-6 years. R(int) was measured at baseline and after each Mch dose. Oxygen saturation (SaO(2)) and transcutaneous oxygen pressure (tcpO(2)) were monitored during the challenge. Mch concentrations of 0.22, 0.66, 2.0, 6.0 and 18.0 mg/ml were nebulised during tidal breathing. The challenge was terminated if there was wheeze, SaO(2) below 91% or persistent cough; this final Mch dose was considered as PCW. Nine healthy children, 17 with cough and 25 with wheeze performed the study up to the point of PCW or all five Mch inhalations. If a change of 20% of predicted R(int) or termination by wheeze, desaturation or cough is taken as a completed test, then 39 out of 51 children (78%) had adequate R(int) measurements on each occasions from start to completion. The success rate for tcpO(2) measurements was similar: 38 out of 51 (76%) had complete tcpO(2) data until a 15% fall of tcpO(2) or clinical endpoint was reached. Using the above-mentioned cut-off levels significant change in R(int) or tcpO(2) preceded PCW in most of the cases. Both R(int) and tcpO(2) measurements may allow detection of bronchial hyper-responsiveness at lower Mch doses and also provide a less subjective measure, but will not be feasible in all children.

Feasibility of shortened methacholine challenge in preschool children.

The aim of our study was to assess the feasibility and safety of a recently suggested tripling-dose methacholine (Mch) challenge in preschool children. Fifty-seven children aged 3-6 years were studied. Mch challenge was carried out using a tidal breathing method, with concentrations of 0.22, 0.66, 2.0, 6.0, and 18.0 mg/ml, at 5-min intervals, given by a Pari Turbo Boy compressor and Pari LC Plus nebulizer, for 1 min only. Oxygen saturation (SaO(2)) was monitored during the challenge. The challenge was terminated if there was wheeze, SaO(2) below 91%, or persistent cough. This final Mch dose was considered the provocative concentration inducing audible wheeze (PCW). Nine healthy children, 17 with cough and 25 with wheeze, completed the study. Mean output from nebulizers (SD) in these 51 children was 0.30 (0.05) ml/min. Geometric means for PCW in these groups were 2.88, 2.58, and 1.28 mg/ml Mch, respectively. The wheezing children were significantly more hyperresponsive than the coughing children (P < 0.05). A tripling-dose Mch protocol is safe and practicable in children over 3 years of age. A further reduction in nebulized dose may be needed for a more discriminatory test.

Lack of association of the alpha2-macroglobulin locus on chromosome 12 in AD.

OBJECTIVE: Analysis of AD has revealed that the apolipoprotein E locus (APOE) cannot account for all of the genetic risk associated with AD. Whole genome scanning in AD families suggests that a chromosome 12 locus may contribute significantly to disease development. The alpha2-macroglobulin gene (A2M) has been suggested as a candidate locus for AD based on analysis of familial AD. METHOD: We determined, in 195 neuropathologically verified AD cases and 107 age-matched control subjects, the association of two common polymorphisms in A2M (a pentanucleotide deletion 5' to the bait domain exon, and a valine-1000-isoleucine polymorphism in the thiolester site of the protein). RESULTS: Evidence was observed for linkage disequilibrium between the deletion and Ile1000 polymorphisms. No evidence was observed for an association between the thiolester polymorphism and AD alone or when accounting for the APOE-epsilon4 allele. No alteration in the frequency of the bait domain deletion was observed, although a small excess (4%) of deletion homozygotes was found in the AD group, which were absent in the control population. CONCLUSIONS: The A2M deletion polymorphism at most accounts for a small fraction of the genetic contribution toward AD, and this is small compared with APOE. Furthermore, reverse transcriptase PCR of A2M RNA from the brains of patients homozygous for the deletion polymorphism showed that the bait domain exon still is present in the RNA. This suggests that the A2M deletion polymorphism may be nonfunctional and that the chromosome 12 AD locus is situated elsewhere.

Degradation of Alzheimer's beta-amyloid protein by human cathepsin D.

The aim of the study was to identify and characterize human brain peptidases capable of degrading Alzheimer's beta-amyloid protein. Synthetic beta-amyloid protein (1-40) was rapidly degraded by a human brain soluble fraction, optimum activity occurring at around pH4. Pepstatin totally inhibited the activity showing that an aspartyl protease was responsible. HPLC separation and identification of the degradation products showed that the L34-M35 bond was the primary site of cleavage followed by hydrolysis of the F19-F20 and F20-A21 bonds. The major lysosomal aspartyl protease, cathepsin D, hydrolysed beta-amyloid protein with the same pH profile, inhibitor sensitivity and bond specificity as the activity present in human brain soluble fraction. We suggest that cathepsin D may play an important role in regulating brain concentrations of beta-amyloid protein (1-40).

Alpha2-macroglobulin polymorphisms in Alzheimer's disease and dementia with Lewy bodies.

Dementia with Lewy bodies (DLB) is the second most common cause of dementia in the elderly after Alzheimer's disease (AD). The apolipoprotein E gene (APOE) is a major risk factor, but can only account for approximately 50% of AD cases. Whole genome scanning in late-onset AD families has suggested that a locus on chromosome 12 may contribute significantly to disease development. Recently the alpha2-macroglobulin gene (A2M) on chromosome 12 has been suggested as a candidate locus for AD. We therefore determined the influence of two polymorphisms in A2M, a pentanucleotide deletion 5' to the bait domain exon, and a valine to isoleucine polymorphism in the thiolester site of the protein, in AD and DLB cohorts. No evidence was observed for an association between the thiolester or deletion polymorphisms and AD or DLB alone or when accounting for the APOE epsilon4 allele. We did, however, identify a non-significant excess of deletion homozygotes in the AD and DLB groups. This genotype accounted for 4% of disease cases but was absent in the control population. Given that the A2M deletion polymorphism is non-functional, the chromosome 12 AD/DLB locus may be situated elsewhere and not with these A2M polymorphisms.

Removal of Arg1 and Phe22 from CLIP (ACTH18-39) by rodent pituitary and blood peptidases.

The major product on incubation of CLIP (ACTH18-39) with rat and mouse serum, rat plasma and whole blood, and soluble extracts of rat pituitary is [des-Arg1]-CLIP (ACTH19-39) while [des-Phe22]-CLIP (ACTH18-38) is the major product with pituitary particulate fraction. In both cases, p-chloromercuribenzoate-sensitive, metal-dependent peptidase activity appears to be responsible for the cleavage. The serum enzyme may be related to proline aminopeptidase. Material coeluting with [des-Arg]-CLIP on two HPLC solvent gradients is present in the superfusion media from neurointermediate lobes of genetically obese (ob/ob) mice but is not present in acid extracts of the lobe. This suggests that postsecretory processing of CLIP may involve removal of the N-terminal Arg residue.

Specificity of action of human brain alanyl aminopeptidase on Leu-enkephalin and dynorphin-related peptides.

The major cystosolic aminopeptidase (alanylaminopeptidase) was purified to homogeneity from human cerebral cortex and the specificity of its actions on a series of Leu-enkephalin-related peptides of increasing chain length was determined. In each case, only the N-terminal Tyr-Gly bond was hydrolysed. Kinetic analysis of the data revealed that the specificity constant (kcat/Km;s-1M-1) falls with increasing chain length from a maximum of 13.6 x 10(4) for Leu-enkephalin (5 residues) to 5.8 x 10(2) for dynorphin (1-13). Dynorphin 1-17, while not being degraded itself acted as a competitive inhibitor (Ki = 2.7 microM) of the degradation of smaller peptides. Beta-endorphin was not hydrolysed by analylaminopeptidase, nor did it act as an inhibitor of the enzyme.

Human brain leucyl aminopeptidase: isolation, characterization and specificity against some neuropeptides.

In order to obtain a greater understanding of the role of aminopeptidases in the degradation of peptides and proteins in the nervous system, we have isolated and characterized leucyl aminopeptidase (EC 3.4.11.1) from human cerebral cortex and studied its action on some physiologically important neuropeptides. The enzyme has a low specificity constant for the hydrolysis of Leu-7-amido-4-methylcoumarin (69s-1M-1) but the peptides Tyr-Gly-Gly and Tyr-Gly-Gly-Phe-Leu (Leu5-enkephalin) were much better substrates (specificity constants 8300 and 18050s -1M-1 respectively). Optimum activity for the degradation of Leu-enkephalin was obtained at pH10.5 in the presence of 5mM-Mn++. A sharp drop in specificity constant occurred with increasing chain length in the series Leu-enkephalin, dynorphin 1-8, 1-10 and 1-13, suggesting that the enzyme functions only as an oligopeptidase. Other neuropeptides were poor substrates (cholecystokinin octapeptide, angiotensin-I) or not hydrolysed at all (somatostatin, Arg8-vasopressin).

Thyrotrophin releasing hormone degradation by rat synaptosomal peptidases: production of the metabolite His-Pro.

The dipeptide, His-Pro, is the major product of the degradation of TRH by rat synaptic membranes in vitro. A small amount of His-Pro is also formed from TRH by the synaptosomal soluble fraction. From inhibitor studies, the main route to His-Pro appears to involve removal of the pGlu residue by membrane-bound metal-dependent pyroglutamylaminopeptidase followed by deamidation. The deamidation step is not mediated by proline endopeptidase (EC3.4.21.26) nor dipeptidylpeptidase-IV (EC3.4.14.5) since it is insensitive to bacitracin and diprotin-A, and may therefore involve a novel membrane-bound TRH metabolizing enzyme. His-Pro is degraded rapidly by the soluble synaptosomal fraction, presumably by prolidase (EC3.4.13.9) and more slowly by the synaptic membrane fraction.

Stability of [D-Trp11]-neurotensin to rat brain peptidases.

The stability of neurotensin (NT) and a potent, long lasting analogue, [D-Trp11]-NT, to rat brain peptidases was compared by incubating the peptides with subcellular fractions (synaptosomes, synaptic membranes) and a purified endopeptidase from rat brain. Degradation of the peptides with time was followed by high performance liquid chromatography (HPLC). The rates of degradation (pmol/min/mg prot.) in synaptosomes were 890 (NT) and 59 [D-Trp11]-NT), and in synaptic membranes were 1180 (NT) and 12 ([D-Trp11]-NT). The main products of the degradation of [D-Trp11]-NT by synaptic peptidases (isolated by HPLC and characterized by amino acid analysis) were the 1-3, 1-4 and 6-13 fragments implying cleavage of [D-Trp11]-NT at the Tyr3-Glu4, Glu4-Asn5 and Asn5-Lys6 bonds. The rates of degradation of NT and [D-Trp11]-NT by the purified endopeptidase from rat brain were 27.2 and 0.76 pmol/min/microliter of enzyme solution respectively. This endopeptidase, which hydrolyses NT at Arg8-Arg9, may be responsible along with other endopeptidases for NT degradation at nerve terminals.

Nitric oxide synthase gene polymorphisms in Alzheimer's disease and dementia with Lewy bodies.

Evidence suggests that vascular and inflammatory components may be important in the aetiology of dementia and genetic risk factors affecting these processes may therefore influence disease development. Recently, polymorphisms in the endothelial constitutive nitric oxide synthase 3 (NOS3) and also the inducible nitric oxide synthase gene (NOS2A) have been suggested to lead to increased risk of Alzheimer's disease (AD) or dementia with Lewy bodies. We have studied the relationship of both these NOS gene polymorphisms to development of AD and dementia with Lewy bodies and find no evidence for association with either condition. We conclude that NOS gene polymorphisms do not alter disease risk in the majority of late-onset dementia cases.

Predicting microbial growth: growth responses of salmonellae in a laboratory medium as affected by pH, sodium chloride and storage temperature.

The growth responses of salmonellae (mixed inoculum of Salmonella thompson, S. stanley and S. infantis) as affected by NaCl concentration, pH level and storage temperature were studied in laboratory medium. Growth curves were obtained at 5 concentrations of NaCl (0.5-4.5%, w/v), 5 pH levels (5.6-6.8) and 5 storage temperatures (10-30 degrees C). Sigmoid curves (Gompertz form) were fitted to the data and the curve parameters used to produce a polynomial model from which predicted growth curves could be generated for any combination of NaCl, pH and storage temperature within the limits studied. From those growth curves values for growth rate, generation time, lag time and other values such as time to a 1000-fold increase in numbers were derived. Such a model offers a cost-effective approach to understanding the microbial growth response in foods, and forms a data-base against which other controlling factors could be evaluated. Some problems of fitting curves to microbial growth data and of modelling such data are discussed.

Predicting fungal growth: the effect of water activity on Aspergillus flavus and related species.

Growth of four species belonging to Aspergillus Section Flavi (A. flavus, A. oryzae, A. parasiticus and A. nomius) was studied at 30 degrees C at ten water activities (aw) between 0.995 and 0.810 adjusted with equal mixtures of glucose and fructose. Colony diameters were measured at intervals and plotted against time. A flexible growth model describing the change in colony diameter (mm) with respect to time was first fitted to the measured growth data and from the fitted curves the maximum colony growth rates were calculated. These values were then fitted with respect to aw to predict colony growth rates at any aw within the range tested. The optimum aw for each species and time to reach a colony diameter of 3 mm were also calculated.

Predicting microbial growth: the consequences of quantity of data.

Having developed a mathematical model of the growth responses in a laboratory medium of salmonellae (mixed inoculum of Salmonella thompson, S stanley and S. infantis) as affected by pH level, NaCl concentration and storage temperature, the consequences of systematic removal of data has been examined. Three-dimensional plots of fitted response surfaces for the whole data set and the data reduced by three strategies highlighted differences between models and illustrated the consequences of using insufficient data. The risk of an erroneous model was demonstrated.

The effect of 100% CO2 on the growth of nonproteolytic Clostridium botulinum at chill temperatures.

The growth of a cocktail of spores from six nonproteolytic Clostridium botulinum type B and E isolates at 5 and 10 degrees C was used to assess the combined effect of NaCl (0.5-4.5% w/v), pH (5.5-6.5) and atmosphere (10% H2:90% N2, 5% CO2:10% H2:85% N2, or 100% CO2) in buffered peptone, yeast, glucose, starch broth with an Eh of approximately -350 mV. Under all atmospheres growth tended to be slower as the concentration of NaCl increased and with NaCl combined with pH levels below 6.0. Of the atmospheres tested, growth occurred at a slower rate and over a narrower range of conditions when C. botulinum was exposed to 100% CO2. This effect was enhanced when the incubation temperature was 5 degrees C. The results indicate that while CO2 decreased C. botulinum growth at chill temperatures, prevention of growth also depended on the NaCl concentration and the pH of the medium.

[Adjuvant treatment in surgery of colon and rectal cancer]. / Tratamientos adyuvantes de la cirugía en el cáncer de colon y recto.

Up to now, there has been no real evidence about the effectiveness of adjuvant surgical treatments in colo-rectal cancer in patients with no evidence of disease. Investigations are frequently out of the rules that must be followed to accept the effectiveness of some treatment. Results with radiotherapy as a loco-regional treatment and chemotherapy or immunotherapy as systemic treatments are contradictory. Our opinion is that, at least in patients with Dukes'C stage, efforts must persist to find the best adjuvant scheme to prolong the free-disease interval, or ideally, increasing the number of patients healed by surgery.