Mental retardation in Down syndrome: From gene dosage imbalance to molecular and cellular mechanisms

Brain metabolic profile assessed by magnetic resonance spectroscopy in ‎‎children with Down syndrome: Relation to intelligence quotient

BACKGROUND

Down syndrome (DS) is one of the most common causes of intellectual disability. Children with DS have varying intelligence quotient (IQ) that can predict their learning abilities.

AIM

To assess the brain metabolic profiles of children with DS and compare them to standard controls, using magnetic resonance spectroscopy (MRS) and correlating the results with IQ.

METHODS

This case-control study included 40 children with DS aged 6-15 years and 40 age and sex-matched healthy children as controls. MRS was used to evaluate ratios of choline/creatine (Cho/Cr), N-acetyl aspartic acid/creatine (NAA/Cr), and myoinositol/creatine (MI/Cr (in the frontal, temporal, and occipital lobes and basal ganglia and compared to controls and correlated with IQ.

RESULTS

Children with DS showed significant reductions in NAA/Cr and MI/Cr and a non-significant reduction in Cho/Cr in frontal lobes compared to controls. Additionally, we observed significant decreases in NAA/Cr, MI/Cr, and Cho/Cr in the temporal and occipital lobes and basal ganglia in children with DS compared to controls. Furthermore, there was a significant correlation between IQ and metabolic ratios in the brains of children with DS.

CONCLUSION

Brain metabolic profile could be a good predictor of IQ in children with DS.

Transcriptomic analysis of stem cells from chorionic villi uncovers the impact of chromosomes 2, 6 and 22 in the clinical manifestations of Down syndrome

BACKGROUND

Down syndrome (DS) clinical multisystem condition is generally considered the result of a genetic imbalance generated by the extra copy of chromosome 21. Recent discoveries, however, demonstrate that the molecular mechanisms activated in DS compared to euploid individuals are more complex than previously thought. Here, we utilize mesenchymal stem cells from chorionic villi (CV) to uncover the role of comprehensive functional genomics-based understanding of DS complexity.

METHODS

Next-generation sequencing coupled with bioinformatic analysis was performed on CV obtained from women carrying fetuses with DS (DS-CV) to reveal specific genome-wide transcriptional changes compared to their euploid counterparts. Functional assays were carried out to confirm the biological processes identified as enriched in DS-CV compared to CV (i.e., cell cycle, proliferation features, immunosuppression and ROS production).

RESULTS

Genes located on chromosomes other than the canonical 21 (Ch. 2, 6 and 22) are responsible for the impairment of life-essential pathways, including cell cycle regulation, innate immune response and reaction to external stimuli were found to be differentially expressed in DS-CV. Experimental validation confirmed the key role of the biological pathways regulated by those genes in the etiology of such a multisystem condition.

CONCLUSIONS

NGS dataset generated in this study highlights the compromised functionality in the proliferative rate and in the innate response of DS-associated clinical conditions and identifies DS-CV as suitable tools for the development of specifically tailored, personalized intervention modalities.

Personalized clinical managements through exploring circulating neural cells and electroencephalography

BACKGROUND

Since an initial diagnosis of Alzheimer disease (AD) in 1907, early detection, was unavailable through 116 years. Up-regulation of V-Ets erythroblastosis virus E26 oncogene homolog 2 (Ets2) is capable to enhance neuronal susceptibility and degeneration. Protein expression (PE) of Ets2 has functional impact on AD and Down's syndrome, with diverse intensity. PE of Ets2 has an influential pathogenic impact on AD. Clinical aspects of neurological disorders directly interact with psychological maladies. However, deterioration requires an early management including programmed based protection.

AIM

To include cell biology in neuro-genetics; personalized, prognostics, predictive, preventive, predisposing (5xP) platform, accompanied by stratifying brain channels behavior pre- and post-intervention by light music in the AD-patients.

METHODS

Include exploration of PE assay and electroencephalography of brain channels. The processes are applied according to: (1) Triangle style, by application of cellular network; and (2) PE assay of Ets2 in the peripheral blood of the patients with AD, by Manual single cell based analysis, and Flow-cytometry. (1) Applying the Genetic counselling and pedigree analysis; (2) considering the psychological status of the referral cases; (3) considering the macro-and/or micro-environmental factors; (4) performing the required Genetics' analysis; and (5) applying the required complementary test(s).

RESULTS

PE of Ets2 has pathogenic role in AD. PE unmasked the nature of heterogeneity/diversity/course of evolution by exploring Ets2, D1853N polymorphism in Ataxia Telangiectasia mutated gene (ATM), vascular endothelial growth factor (VEGF), epidermal growth factor (EGF) and course of evolution at the single cell level of the brain. Ets2 revealed different cellular behavior in the blood and suggested the strategy as 'Gene Product-Based Therapy' and the personalized managements for the patients. PE reflected weak expression of ATM, mosaic pattern of Ets2; remarkable expression of VEGF and EGF by highlighting an early detective platform, considering circulating neural cells (CNCs) and the required molecular investigation, for the target individual(s) predisposed to AD or other neural disease including brain neoplasia. Brain channels-cooperation with diverse/interactive-ratios lead to strategic balancing for improving the life-quality in AD.

CONCLUSION

We highlighted application of the single CNCs and correlated Ratio based between Brain channels by providing the 5xP personalized clinical management model for an early detection and therapy of the patients with AD and their targeted/predisposed relatives. Novel-evolutionary/hypothetic/heterogenic-results in brain-channels offer personalizd/constructive markers with unlimited cooperation in health and disease.

A lightweight CNN and Transformer hybrid model for mental retardation screening among children from spontaneous speech

Mental retardation (MR) is a group of mental disorders characterized by low intelligence and social adjustment difficulties. Early diagnosis is beneficial for the timely intervention of children with MR to ease the degree of disability. Children with MR always have impaired speech functions compared to normal children, which is significant for clinical diagnosis. On the basis of this, our study proposes a spontaneous speech-based framework (MT-Net) for screening MR, which merges mobile inverted bottleneck convolutional blocks (MBConv) and visual Transformer blocks. MT-Net takes log-mel spectrograms converted from raw interview speech as data source, and utilizes MBConv and visual Transformer to learn low-level and high-level features well. In addition, SpecAugment, a data augmentation strategy, has been used to expand our audio dataset to further enhance the performance of MT-Net. The experimental results show that our proposed MT-Net outperforms Transformer networks (ViT) and convolutional neural networks (ResNet18, MobileNetV2, EfficientNetV2), achieving accuracy of 91.60% after using SpecAugment. Our proposed MT-Net has fewer parameters, low computing consumption and high prediction accuracy, which is expected to be an auxiliary screening tool for MR.

Noninvasive amino acid turnover predicts human embryo aneuploidy

Assisted reproduction technology has two significant problems: low success rates and multiple pregnancies. Because of these problems, the priority in IVF clinics is to develop a potential diagnostic test that can be used to select the embryos with the ultimate developmental competence. Aneuploidy screening as embryo selection criteria will ensure that the transferred embryos are euploid and high implantation rate. We hypothesize that aneuploidy in human preimplantation embryos could be discriminated by their amino acid metabolism profile in the spent culture media. Preimplantation genetic testing for aneuploidy results and spent embryo culture medium amino acid content were analyzed for 58 couples. The next-generation sequencing technique was used and coupled with TE biopsy. Forty euploid and 71 aneuploid blastocysts were evaluated. Embryos were cultured individually until day 5 or 6 of embryo development. Spent culture medium was collected after finishing the culture. There was no statistical difference between D3 and D5 embryo morphology between euploid and aneuploid embryos (p > .05). Eight amino acids, including SER, GLY, HIS, ARG, THR, ALA, PRO, and TYR, were detected in the culture medium from the blank control group, euploid group, and aneuploid group. Only TYR amino acid concentration was found significantly higher in the aneuploid group compared to the euploid group (p < .003). Tyrosine amino acid levels equal to and above 76.38 µmol/L could be considered aneuploid. Aneuploid embryos demonstrate altered amino acid turnover in vitro relative to euploid counterparts. A noninvasive method of amino acid profiling will be of value as a tool for routine preimplantation embryo selection among all patient groups.

Down-Klinefelter Syndrome (48,XXY,+21) in a Saudi Neonate: A Case Report and Literature Review

Aneuploidy is a category of chromosomal abnormalities involving a numerical abnormality of the chromosomes. The most common type seen in live-born babies is trisomy. Double aneuploidy that leads to trisomy of two different chromosomes occurs due to accidental meiotic nondisjunction events; both can have the same or a different parental origin. Other frequently found double aneuploidies include 48,XXX,+21; 48,XXY,+18, and 48,XXX,+18. Here, we report the case of double aneuploidy (Down-Klinefelter syndrome) in a Saudi newborn with the clinical features of Down syndrome, along with hypothyroidism and congenital heart disease, who was admitted to our neonatal intensive care unit. To our knowledge, this is the first case of its kind reported from the Kingdom of Saudi Arabia.

Novel method for trisomy 21 screening in the first trimester of pregnancy: fetal brain angle

OBJECTIVES

The present study was performed to examine the utility of a new first trimester marker called the "brain angle" (BA) in screening for trisomy 21. We postulate that differences in the midbrain anatomy between euploid fetuses and those that are affected by trisomy 21 are reflected in changes in BA measurements.

METHODS

In fetuses at 11⁺⁰-13⁺⁶ weeks of gestations, which were at high risk for trisomy 21, the angle was measured between the line crossing the thalamus and mesencephalon cranial border tangentially and the line crossing the brainstem lower limit. This angle was compared between fetuses with trisomy 21 (based on karyotyping) and those with a normal karyotype.

RESULTS

Trisomy 21 was detected in 45 (8%) of 560 fetuses. Receiver operating characteristic analysis showed that, at BA≥94°, the sensitivity and specificity for determining trisomy 21 were 97.8% (95% CI=88.2-99.9%) and 100% (95% CI=99.2-100%), respectively.

CONCLUSIONS

Fetal BA appears to be a promising new first trimester marker in screening for trisomy 21.

Determinants of trafficking, conduction, and disease within a K+ channel revealed through multiparametric deep mutational scanning

A long-standing goal in protein science and clinical genetics is to develop quantitative models of sequence, structure, and function relationships to understand how mutations cause disease. Deep mutational scanning (DMS) is a promising strategy to map how amino acids contribute to protein structure and function and to advance clinical variant interpretation. Here, we introduce 7429 single-residue missense mutations into the inward rectifier K⁺ channel Kir2.1 and determine how this affects folding, assembly, and trafficking, as well as regulation by allosteric ligands and ion conduction. Our data provide high-resolution information on a cotranslationally folded biogenic unit, trafficking and quality control signals, and segregated roles of different structural elements in fold stability and function. We show that Kir2.1 surface trafficking mutants are underrepresented in variant effect databases, which has implications for clinical practice. By comparing fitness scores with expert-reviewed variant effects, we can predict the pathogenicity of 'variants of unknown significance' and disease mechanisms of known pathogenic mutations. Our study in Kir2.1 provides a blueprint for how multiparametric DMS can help us understand the mechanistic basis of genetic disorders and the structure-function relationships of proteins.

Neurometabolite mapping highlights elevated myo-inositol profiles within the developing brain in down syndrome

The neurodevelopmental phenotype in Down Syndrome (DS), or Trisomy 21, is variable including a wide spectrum of cognitive impairment and a high risk of early-onset Alzheimer's disease (AD). A key metabolite of interest within the brain in DS is Myo-inositol (mIns). The NA+/mIns co-transporter is located on human chromosome 21 and is overexpressed in DS. In adults with DS, elevated brain mIns was previously associated with cognitive impairment and proposed as a risk marker for progression to AD. However, it is unknown if brain mIns is increased earlier in development. The aim of this study was to estimate mIns concentration levels and key brain metabolites [N-acetylaspartate (NAA), Choline (Cho) and Creatine (Cr)] in the developing brain in DS and aged-matched controls. We used in vivo magnetic resonance spectroscopy (MRS) in neonates with DS (n = 12) and age-matched controls (n = 26) scanned just after birth (36-45 weeks postmenstrual age). Moreover, we used Mass Spectrometry in early (10-20 weeks post conception) ex vivo fetal brain tissue samples from DS (n = 14) and control (n = 30) cases. Relative to [Cho] and [Cr], we report elevated ratios of [mIns] in vivo in the basal ganglia/thalamus, in neonates with DS, when compared to age-matched typically developing controls. Glycine concentration ratios [Gly]/[Cr] and [Cho]/[Cr] also appear elevated. We observed elevated [mIns] in the ex vivo fetal cortical brain tissue in DS compared with controls. In conclusion, a higher level of brain mIns was evident as early as 10 weeks post conception and was measurable in vivo from 36 weeks post-menstrual age. Future work will determine if this early difference in metabolites is linked to cognitive outcomes in childhood or has utility as a potential treatment biomarker for early intervention.

A multi-level developmental approach to exploring individual differences in Down syndrome: genes, brain, behaviour, and environment

In this article, we focus on the causes of individual differences in Down syndrome (DS), exemplifying the multi-level, multi-method, lifespan developmental approach advocated by Karmiloff-Smith (1998, 2009, 2012, 2016). We evaluate the possibility of linking variations in infant and child development with variations in the (elevated) risk for Alzheimer's disease (AD) in adults with DS. We review the theoretical basis for this argument, considering genetics, epigenetics, brain, behaviour and environment. In studies 1 and 2, we focus on variation in language development. We utilise data from the MacArthur-Bates Communicative Development Inventories (CDI; Fenson et al., 2007), and Mullen Scales of Early Learning (MSEL) receptive and productive language subscales (Mullen, 1995) from 84 infants and children with DS (mean age 2;3, range 0;7 to 5;3). As expected, there was developmental delay in both receptive and expressive vocabulary and wide individual differences. Study 1 examined the influence of an environmental measure (socio-economic status as measured by parental occupation) on the observed variability. SES did not predict a reliable amount of the variation. Study 2 examined the predictive power of a specific genetic measure (apolipoprotein APOE genotype) which modulates risk for AD in adulthood. There was no reliable effect of APOE genotype, though weak evidence that development was faster for the genotype conferring greater AD risk (ε4 carriers), consistent with recent observations in infant attention (D'Souza, Mason et al., 2020). Study 3 considered the concerted effect of the DS genotype on early brain development. We describe new magnetic resonance imaging methods for measuring prenatal and neonatal brain structure in DS (e.g., volumes of supratentorial brain, cortex, cerebellar volume; Patkee et al., 2019). We establish the methodological viability of linking differences in early brain structure to measures of infant cognitive development, measured by the MSEL, as a potential early marker of clinical relevance. Five case studies are presented as proof of concept, but these are as yet too few to discern a pattern.

Down Syndrome Is a Metabolic Disease: Altered Insulin Signaling Mediates Peripheral and Brain Dysfunctions

Down syndrome (DS) is the most frequent chromosomal abnormality that causes intellectual disability, resulting from the presence of an extra complete or segment of chromosome 21 (HSA21). In addition, trisomy of HSA21 contributes to altered energy metabolism that appears to be a strong determinant in the development of pathological phenotypes associated with DS. Alterations include, among others, mitochondrial defects, increased oxidative stress levels, impaired glucose, and lipid metabolism, finally resulting in reduced energy production and cellular dysfunctions. These molecular defects seem to account for a high incidence of metabolic disorders, i.e., diabetes and/or obesity, as well as a higher risk of developing Alzheimer’s disease (AD) in DS. A dysregulation of the insulin signaling with reduced downstream pathways represents a common pathophysiological aspect in the development of both peripheral and central alterations leading to diabetes/obesity and AD. This is further strengthened by evidence showing that the molecular mechanisms responsible for such alterations appear to be similar between peripheral organs and brain. Considering that DS subjects are at high risk to develop either peripheral or brain metabolic defects, this review will discuss current knowledge about the link between trisomy of HSA21 and defects of insulin and insulin-related pathways in DS. Drawing the molecular signature underlying these processes in DS is a key challenge to identify novel drug targets and set up new prevention strategies aimed to reduce the impact of metabolic disorders and cognitive decline.

Targeting Mitochondrial Network Architecture in Down Syndrome and Aging

Mitochondria are organelles that mainly control energy conversion in the cell. In addition, they also participate in many relevant activities, such as the regulation of apoptosis and calcium levels, and other metabolic tasks, all closely linked to cell viability. Functionality of mitochondria appears to depend upon their network architecture that may dynamically pass from an interconnected structure with long tubular units, to a fragmented one with short separate fragments. A decline in mitochondrial quality, which presents itself as an altered structural organization and a function of mitochondria, has been observed in Down syndrome (DS), as well as in aging and in age-related pathologies. This review provides a basic overview of mitochondrial dynamics, from fission/fusion mechanisms to mitochondrial homeostasis. Molecular mechanisms determining the disruption of the mitochondrial phenotype in DS and aging are discussed. The impaired activity of the transcriptional co-activator PGC-1α/PPARGC1A and the hyperactivation of the mammalian target of rapamycin (mTOR) kinase are emerging as molecular underlying causes of these mitochondrial alterations. It is, therefore, likely that either stimulating the PGC-1α activity or inhibiting mTOR signaling could reverse mitochondrial dysfunction. Evidence is summarized suggesting that drugs targeting either these pathways or other factors affecting the mitochondrial network may represent therapeutic approaches to improve and/or prevent the effects of altered mitochondrial function. Overall, from all these studies it emerges that the implementation of such strategies may exert protective effects in DS and age-related diseases.

Early alterations in cortical and cerebellar regional brain growth in Down Syndrome: An in vivo fetal and neonatal MRI assessment

Down Syndrome (DS) is the most frequent genetic cause of intellectual disability with a wide spectrum of neurodevelopmental outcomes. At present, the relationship between structural brain morphology and the spectrum of cognitive phenotypes in DS, is not well understood. This study aimed to quantify the development of the fetal and neonatal brain in DS participants, with and without a congenital cardiac defect compared with a control population using dedicated, optimised and motion-corrected in vivo magnetic resonance imaging (MRI). We detected deviations in development and altered regional brain growth in the fetus with DS from 21 weeks' gestation, when compared to age-matched controls. Reduced cerebellar volume was apparent in the second trimester with significant alteration in cortical growth becoming evident during the third trimester. Developmental abnormalities in the cortex and cerebellum are likely substrates for later neurocognitive impairment, and ongoing studies will allow us to confirm the role of antenatal MRI as an early biomarker for subsequent cognitive ability in DS. In the era of rapidly developing technologies, we believe that the results of this study will assist counselling for prospective parents.

Early alterations in cortical and cerebellar regional brain growth in Down Syndrome: An in vivo fetal and neonatal MRI assessment

Down Syndrome (DS) is the most frequent genetic cause of intellectual disability with a wide spectrum of neurodevelopmental outcomes. At present, the relationship between structural brain morphology and the spectrum of cognitive phenotypes in DS, is not well understood. This study aimed to quantify the development of the fetal and neonatal brain in DS participants, with and without a congenital cardiac defect compared with a control population using dedicated, optimised and motion-corrected in vivo magnetic resonance imaging (MRI). We detected deviations in development and altered regional brain growth in the fetus with DS from 21 weeks' gestation, when compared to age-matched controls. Reduced cerebellar volume was apparent in the second trimester with significant alteration in cortical growth becoming evident during the third trimester. Developmental abnormalities in the cortex and cerebellum are likely substrates for later neurocognitive impairment, and ongoing studies will allow us to confirm the role of antenatal MRI as an early biomarker for subsequent cognitive ability in DS. In the era of rapidly developing technologies, we believe that the results of this study will assist counselling for prospective parents.

Single cell transcriptome in aneuploidies reveals mechanisms of gene dosage imbalance

Aneuploidy is a major source of gene dosage imbalance due to copy number alterations (CNA), and viable human trisomies are model disorders of altered gene expression. We study gene and allele-specific expression (ASE) of 9668 single-cell fibroblasts from trisomy 21 (T21) discordant twins and from mosaic T21, T18, T13 and T8. We examine 928 single cells with deep scRNAseq. Expected and observed overexpression of trisomic genes in trisomic vs. diploid bulk RNAseq is not detectable in trisomic vs. diploid single cells. Instead, for trisomic genes with low-to-average expression, their altered gene dosage is mainly due to the higher fraction of trisomic cells simultaneously expressing these genes, in agreement with a stochastic 2-state burst-like model of transcription. These results, confirmed in a further analysis of 8740 single fibroblasts with shallow scRNAseq, suggest that the specific transcriptional profile of each gene contributes to the phenotypic variability of trisomies. We propose an improved model to understand the effects of CNA and, generally, of gene regulation on gene dosage imbalance.

Investigating Potassium Channels in Budding Yeast: A Genetic Sandbox

Like all species, the model eukaryote Saccharomyces cerevisiae, or Bakers' yeast, concentrates potassium in the cytosol as an electrogenic osmolyte and enzyme cofactor. Yeast are capable of robust growth on a wide variety of potassium concentrations, ranging from 10 µM to 2.5 M, due to the presence of a high-affinity potassium uptake system and a battery of cation exchange transporters. Genetic perturbation of either of these systems retards yeast growth on low or high potassium, respectively. However, these potassium-sensitized yeast are a powerful genetic tool, which has been leveraged for diverse studies. Notably, the potassium-sensitive cells can be transformed with plasmids encoding potassium channels from bacteria, plants, or mammals, and subsequent changes in growth rate have been found to correlate with the activity of the introduced potassium channel. Discoveries arising from the use of this assay over the past three decades have increased our understanding of the structure-function relationships of various potassium channels, the mechanisms underlying the regulation of potassium channel function and trafficking, and the chemical basis of potassium channel modulation. In this article, we provide an overview of the major genetic tools used to study potassium channels in S. cerevisiae, a survey of seminal studies utilizing these tools, and a prospective for the future use of this elegant genetic approach.

Establishment of a human trisomy 18 induced pluripotent stem cell line from amniotic fluid cells

Trisomy 18 (18T) is the second most common autosomal trisomy syndrome in humans, but the detailed mechanism of its pathology remains unclear due to the lack of appropriate models of this disease. To resolve this problem, the current study reprogrammed human 18T amniotic fluid cells (AFCs) into an induced pluripotent stem cell (iPSC) line by introducing integration-free episomal vectors carrying pCXLE-hOCT3/4-shp53-F, pCXLE-hSK, pCXLE-hUL, and pCXWB-EBNA1. The pluripotency of 18T-iPSCs was subsequently validated by alkaline phosphatase staining, detection of iPSC biomarkers using real-time PCR and flow cytometry, detection of embryoid body (EB) formation, and detection of in vivo teratoma formation. Moreover, this study also investigated the transcriptomic profiles of 18T-iPSCs using RNA sequencing, and several gene clusters associated with the clinical manifestations of 18T were identified. In summary, the generated induced pluripotent stem cells line has typical pluripotency characteristics and can provide a useful tool with which to understand the development of 18T.

Mitochondrial dysfunction in down syndrome: molecular mechanisms and therapeutic targets

Trisomy of chromosome 21 (TS21) is the most common autosomal aneuploidy compatible with postnatal survival with a prevalence of 1 in 700 newborns. Its phenotype is highly complex with constant features, such as mental retardation, dysmorphic traits and hypotonia, and variable features including heart defects, susceptibility to Alzheimer’s disease (AD), type 2 diabetes, obesity and immune disorders. Overexpression of genes on chromosome-21 (Hsa21) is responsible for the pathogenesis of Down syndrome (DS) phenotypic features either in a direct or in an indirect manner since many Hsa21 genes can affect the expression of other genes mapping to different chromosomes. Many of these genes are involved in mitochondrial function and energy conversion, and play a central role in the mitochondrial dysfunction and chronic oxidative stress, consistently observed in DS subjects.

Recent studies highlight the deep interconnections between mitochondrial dysfunction and DS phenotype. In this short review we first provide a basic overview of mitochondrial phenotype in DS cells and tissues. We then discuss how specific Hsa21 genes may be involved in determining the disruption of mitochondrial DS phenotype and biogenesis. Finally we briefly focus on drugs that affect mitochondrial function and mitochondrial network suggesting possible therapeutic approaches to improve and/or prevent some aspects of the DS phenotype.

Muscle stem cell dysfunction impairs muscle regeneration in a mouse model of Down syndrome

Down syndrome, caused by trisomy 21, is characterized by a variety of medical conditions including intellectual impairments, cardiovascular defects, blood cell disorders and pre-mature aging phenotypes. Several somatic stem cell populations are dysfunctional in Down syndrome and their deficiencies may contribute to multiple Down syndrome phenotypes. Down syndrome is associated with muscle weakness but skeletal muscle stem cells or satellite cells in Down syndrome have not been investigated. We find that a failure in satellite cell expansion impairs muscle regeneration in the Ts65Dn mouse model of Down syndrome. Ts65Dn satellite cells accumulate DNA damage and over express Usp16, a histone de-ubiquitinating enzyme that regulates the DNA damage response. Impairment of satellite cell function, which further declines as Ts65Dn mice age, underscores stem cell deficiencies as an important contributor to Down syndrome pathologies.

Mitochondria as pharmacological targets in Down syndrome

Mitochondria play a pivotal role in cellular energy-generating processes and are considered master regulators of cell life and death fate. Mitochondrial function integrates signalling networks in several metabolic pathways controlling neurogenesis and neuroplasticity. Indeed, dysfunctional mitochondria and mitochondrial-dependent activation of intracellular stress cascades are critical initiating events in many human neurodegenerative or neurodevelopmental diseases including Down syndrome (DS). It is well established that trisomy of human chromosome 21 can cause DS. DS is associated with neurodevelopmental delay, intellectual disability and early neurodegeneration. Recently, molecular mechanisms responsible for mitochondrial damage and energy deficits have been identified and characterized in several DS-derived human cells and animal models of DS. Therefore, therapeutic strategies targeting mitochondria could have great potential for new treatment regimens in DS. The purpose of this review is to highlight recent studies concerning mitochondrial impairment in DS, focusing on alterations of the molecular pathways controlling mitochondrial function. We will also discuss the effects and molecular mechanisms of naturally occurring and chemically synthetized drugs that exert neuroprotective effects through modulation of mitochondrial function and attenuation of oxidative stress. These compounds might represent novel therapeutic tools for the modulation of energy deficits in DS.

Isolation of proflavine as a blocker of G protein-gated inward rectifier potassium channels by a cell growth-based screening system

The overexpression of Kir3.2, a subunit of the G protein-gated inwardly rectifying K(+) channel, is implicated in some of the neurological phenotypes of Down syndrome (DS). Chemical compounds that block Kir3.2 are expected to improve the symptoms of DS. The purpose of this study is to develop a cell-based screening system to identify Kir3.2 blockers and then investigate the mode of action of the blocker. Chemical screening was carried out using a K(+) transporter-deficient yeast strain that expressed a constitutively active Kir3.2 mutant. The mode of action of an effective blocker was electrophysiologically analyzed using Kir channels expressed in Xenopus oocytes. Proflavine was identified to inhibit the growth of Kir3.2-transformant cells and Kir3.2 activity in a concentration-dependent manner. The current inhibition was strong when membrane potentials (Vm) was above equilibrium potential of K(+) (EK). When Vm was below EK, the blockage apparently depended on the difference between Vm and [K(+)]. Furthermore, the inhibition became stronger by lowering extracellular [K(+)]. These results indicated that the yeast strain serves as a screening system to isolate Kir3.2 blockers and proflavine is a prototype of a pore blocker of Kir3.2.

Aneuploidy: the impact of chromosome imbalance on nuclear organization and overall genome expression

The organization and dynamics of chromatin within the interphase nucleus as chromosome territories (CTs) and the relationship with transcriptional regulation are not fully understood. We studied a natural example of chromosomal disorganization: aneuploidy due to trisomies 13, 18 and 21. We hypothesized that the presence of an extra copy of one chromosome alters the CT distribution, which perturbs transcriptional activity. We used 3D-FISH to study the position of the chromosomes of interest (18 and 21) in cultured amniocytes and chorionic villus cells from pregnancies with a normal or aneuploid karyotype. We studied the volumes of nuclei and CTs in both conditions and performed a compared transcriptome analysis. We did not observe any differences between euploid and aneuploid cells in terms of the radial and relative CT positions, suggesting that the same rules govern nuclear organization in cases of trisomy. We observed lower volumes for CTs 18 and 21. Overall genome expression profiles highlighted changes in the expression of a subset of genes in trisomic chromosomes, while the majority of transcriptional changes concerned genes located on euploid chromosomes. Our results suggest that a dosage imbalance of the genes on trisomic chromosomes is associated with a disturbance of overall genomic expression.

Receptor-interacting protein 140 overexpression promotes neuro-2a neuronal differentiation by ERK1/2 signaling

Background:

Abnormal neuronal differentiation plays an important role in central nervous system (CNS) development abnormalities such as Down syndrome (DS), a disorder that results directly from overexpression of genes in trisomic cells. Receptor-interacting protein 140 (RIP140) is significantly upregulated in DS brains, suggesting its involvement in DS CNS development abnormalities. However, the role of RIP140 in neuronal differentiation is still not clear. The current study aimed to investigate the effect of RIP140 overexpression on the differentiation of neuro-2a (N2a) neuroblastoma cells, in vitro.

Methods:

Stably RIP140-overexpressing N2a (N2a-RIP140) cells were used as a neurodevelopmental model, and were constructed by lipofection and overexpression validated by real-time polymerase chain reaction and Western blot. Retinoic acid (RA) was used to stimulate N2a differentiation. Combining the expression of Tuj1 at the mRNA and protein levels, the percentage of cells baring neurites, and the number of neurites per cell body was semi-quantified to determine the effect of RIP140 on differentiation of N2a cells. Furthermore, western blot and the ERK1/2 inhibitor U0126 were used to identify the specific signaling pathway by which RIP140 induces differentiation of N2a cells. Statistical significance of the differences between groups was determined by one-way analysis of variance followed by the Dunnett test.

Results:

Compared to untransfected N2a cells RIPl40 expression in N2a-RIP140 cells was remarkably upregulated at both the mRNA and protein levels. N2a-RIP140 cells had a significantly increased percentage of cells baring neurites, and numbers of neurites per cell, as compared to N2a cells, in the absence and presence of RA (P < 0.05). In addition, Tuj1, a neuronal biomarker, was strongly upregulated in N2a-RIP140 cells (P < 0.05) and phosphorylated ERK1/2 (p-ERK1/2) levels in N2a-RIP140 cells were dramatically increased, while differentiation was inhibited by the ERK1/2-specific inhibitor U0126.

Conclusions:

RIP140 overexpression promotes N2a cell neuronal differentiation by activating the ERK1/2 pathway.

Down Syndrome Cognitive Phenotypes Modeled in Mice Trisomic for All HSA 21 Homologues

Down syndrome (DS), trisomy for chromosome 21, is the most common genetic cause of intellectual disability. The genomic regions on human chromosome 21 (HSA21) are syntenically conserved with regions on mouse chromosomes 10, 16, and 17 (Mmu10, Mmu16, and Mmu17). Recently, we created a genetic model of DS which carries engineered duplications of all three mouse syntenic regions homologous to HSA21. This 'triple trisomic' or TTS model thus represents the most complete and accurate murine model currently available for experimental studies of genotype-phenotype relationships in DS. Here we extended our initial studies of TTS mice. Locomotor activity, stereotypic and repetitive behavior, anxiety, working memory, long-term memory, and synaptic plasticity in the dentate gyrus were examined in the TTS and wild-type (WT) control mice. Changes in locomotor activity were most remarkable for a significant increase in ambulatory time and a reduction in average velocity of TTS mice. No changes were detected in repetitive and stereotypic behavior and in measures of anxiety. Working memory showed no changes when tested in Y-maze, but deficiency in a more challenging T-maze test was detected. Furthermore, long-term object recognition memory was significantly reduced in the TTS mice. These changes were accompanied by deficient long-term potentiation in the dentate gyrus, which was restored to the WT levels following blockade of GABAA receptors with picrotoxin (100 μM). TTS mice thus demonstrated a number of phenotypes characteristic of DS and may serve as a new standard by which to evaluate and direct findings in other less complete models of DS.

Aneuploid proliferation defects in yeast are not driven by copy number changes of a few dosage-sensitive genes

A central question is whether aneuploid phenotypes are the consequence of copy number changes of a few especially harmful genes that may be present on the extra chromosome or are caused by copy number alterations of many genes that confer no observable phenotype when varied individually. Bonney et al. used the proliferation defect exhibited by budding yeast strains carrying single additional chromosomes (disomes) to show that subtle changes in gene dosage across a chromosome can have significant phenotypic consequences.

Aneuploidy—the gain or loss of one or more whole chromosome—typically has an adverse impact on organismal fitness, manifest in conditions such as Down syndrome. A central question is whether aneuploid phenotypes are the consequence of copy number changes of a few especially harmful genes that may be present on the extra chromosome or are caused by copy number alterations of many genes that confer no observable phenotype when varied individually. We used the proliferation defect exhibited by budding yeast strains carrying single additional chromosomes (disomes) to distinguish between the “few critical genes” hypothesis and the “mass action of genes” hypothesis. Our results indicate that subtle changes in gene dosage across a chromosome can have significant phenotypic consequences. We conclude that phenotypic thresholds can be crossed by mass action of copy number changes that, on their own, are benign.

Neuropsychological late effects of treatment for acute leukemia in children with Down syndrome

BACKGROUND

Children with Down syndrome (DS) have an elevated risk of developing acute leukemia, but little is known about treatment-related neuropsychological morbidity because they are systematically excluded from research in this area. The current study investigated neuropsychological outcomes in children with DS treated for acute lymphoblastic leukemia (ALL) or acute myeloid leukemia (AML) compared to children with DS with no history of cancer.

PROCEDURE

Participants were 4 to 17 years of age at testing and were administered measures of intelligence, academic achievement, language, visual-motor and fine-motor skills, and adaptive function. Patients had been off treatment for at least 2 years.

RESULTS

The AML group (N = 12) had significantly lower verbal intelligence and receptive vocabulary compared to controls (N = 21). By contrast, the ALL group (N = 14) performed significantly worse than controls on measures of verbal intelligence, spelling, receptive and expressive vocabulary, visual-motor skills, and adaptive function.

CONCLUSIONS

Patients with DS treated for AML may have specific post-treatment morbidity in verbal function, whereas those treated for ALL have broader morbidity affecting multiple neuropsychological domains and overall adaptive function. We hypothesize that the broader impairment profile of ALL survivors may be related to a combination of the longer duration of central nervous system-directed treatment for ALL compared to AML and the concomitant limited access to intervention opportunities during active treatment.

Nest building is impaired in the Ts65Dn mouse model of Down syndrome and rescued by blocking 5HT2a receptors

Down syndrome (DS) has an incidence of about 1/700 births, and is therefore the most common cause of cognitive and behavioral impairments in children. Recent studies on mouse models of DS indicate that a number of pharmacotherapies could be beneficial for restoring cognitive abilities in individuals with DS. Attention deficits that are present in DS account in part for learning and memory deficiencies yet have been scarcely studied in corresponding models. Investigations of this relevant group of behaviors is more difficult in mouse models because of the difficulty in homologizing mouse and human behaviors and because standard laboratory environments do not always elicit behaviors of interest. Here we characterize nest building as a goal-directed behavior that is seriously impaired in young Ts65Dn mice, a genetic model of DS. We believe this impairment may reflect in part attention deficits, and we investigate the physiological, genetic, and pharmacological factors influencing its expression. Nesting behavior in young Ts65Dn mice was severely impaired when the animals were placed in a novel environment. But this context-dependent impairment was transient and reversible. The genetic determinants of this deficiency are restricted to a ∼100 gene segment on the murine chromosome 16. Nest building behavior is a highly integrated phenotypic trait that relies in part on limbic circuitry and on the frontal cortex in relation to cognitive and attention processes. We show that both serotonin content and 5HT2a receptors are increased in the frontal cortex of Ts65Dn mice and that pharmacological blockage of 5HT2a receptors in Ts65Dn mice rescues their context dependent nest building impairment. We propose that the nest-building trait could represent a marker of attention related deficits in DS models and could be of value in designing pharmacotherapies for this specific aspect of DS. 5HT2a modulation may improve goal-directed behavior in DS.

The association between behavioural and emotional problems and age in adults with Down syndrome without dementia: Examining a wide spectrum of behavioural and emotional problems

The literature on the association between behavioural and emotional problems and ageing in adults with Down syndrome (DS) without dementia is limited and has generally not reported on a wide range of behavioural and emotional problems. This research aimed to extend the field by examining the associations between age and a wide spectrum of behavioural and emotional problems in adults with DS without dementia. A preliminary analysis of the association between potential covariates and behavioural and emotional problems was also undertaken. Parents and caregivers completed a questionnaire on behavioural and emotional problems for 53 adults with DS aged between 16 and 56 years. Twenty-eight adults with DS and their caregivers were part of a longitudinal sample, which provided two time points of data approximately four years apart. Additionally, 25 participants with DS and their caregivers were from a cross sectional sample, which provided one time point of data. Random effects regression analyses were used to examine the patterns in item scores for behavioural and emotional problems associated with age. No significant associations between age and the range or severity of any behavioural and emotional items were found. This suggested a more positive pattern for ageing adults with DS than has been previously described. Given that behavioural and emotional problems were not associated with age, investigation into other factors that may be associated with the behavioural and emotional difficulties for adults with DS is discussed.

Impairment of translation in neurons as a putative causative factor for autism

BACKGROUND

A dramatic increase in the prevalence of autism and Autistic Spectrum Disorders (ASD) has been observed over the last two decades in USA, Europe and Asia. Given the accumulating data on the possible role of translation in the etiology of ASD, we analyzed potential effects of rare synonymous substitutions associated with ASD on mRNA stability, splicing enhancers and silencers, and codon usage.

PRESENTATION OF THE HYPOTHESIS

We hypothesize that subtle impairment of translation, resulting in dosage imbalance of neuron-specific proteins, contributes to the etiology of ASD synergistically with environmental neurotoxins.

TESTING THE HYPOTHESIS

A statistically significant shift from optimal to suboptimal codons caused by rare synonymous substitutions associated with ASD was detected whereas no effect on other analyzed characteristics of transcripts was identified. This result suggests that the impact of rare codons on the translation of genes involved in neuron development, even if slight in magnitude, could contribute to the pathogenesis of ASD in the presence of an aggressive chemical background. This hypothesis could be tested by further analysis of ASD-associated mutations, direct biochemical characterization of their effects, and assessment of in vivo effects on animal models.

IMPLICATIONS OF THE HYPOTHESIS

It seems likely that the synergistic action of environmental hazards with genetic variations that in themselves have limited or no deleterious effects but are potentiated by the environmental factors is a general principle that underlies the alarming increase in the ASD prevalence.

REVIEWERS

This article was reviewed by Andrey Rzhetsky, Neil R. Smalheiser, and Shamil R. Sunyaev.

Drosophila models of early onset cognitive disorders and their clinical applications

The number of genes known to cause human monogenic diseases is increasing rapidly. For the extremely large, genetically and phenotypically heterogeneous group of intellectual disability (ID) disorders, more than 600 causative genes have been identified to date. However, knowledge about the molecular mechanisms and networks disrupted by these genetic aberrations is lagging behind. The fruit fly Drosophila has emerged as a powerful model organism to close this knowledge gap. This review summarizes recent achievements that have been made in this model and envisions its future contribution to our understanding of ID genetics and neuropathology. The available resources and efficiency of Drosophila place it in a position to tackle the main challenges in the field: mapping functional modules of ID genes to provide conceptually novel insights into the genetic control of cognition, tailored functional studies to improve 'next-generation' diagnostics, and identification of reversible ID phenotypes and medication. Drosophila's behavioral repertoire and powerful genetics also open up perspectives for modeling genetically complex forms of ID and neuropsychiatric disorders, which overlap in their genetic etiologies. In conclusion, Drosophila provides many opportunities to advance future medical genomics of early onset cognitive disorders.

Structural and functional analysis of single neurons to correlate synaptic connectivity with grooming behavior

We describe a protocol to image the complex axonal branching structure of identified mechanosensory neurons in Drosophila, combined with a behavioral assay to evaluate the functional output of the neuron. The stimulation of identified mechanosensory neurons in live animals produces a stereotyped grooming reflex. The mechanosensory axonal arbor within the CNS is subsequently labeled with a lipophilic fluorescent dye and imaged by fluorescence microscopy. The behavioral output can therefore be correlated to the axonal morphology of the stimulated neuron in the same animal. Combining this protocol with genetic analysis provides a powerful tool for identifying the roles of molecules involved in different aspects of hard-wired neural circuit formation underlying an innate behavior. From behavioral analysis to axonal imaging, the protocol takes 4 d.

Overexpression of Down syndrome cell adhesion molecule impairs precise synaptic targeting

Fragile X syndrome is caused by loss of Fragile X Mental Retardation Protein (FMRP), an RNA binding protein that suppresses protein translation. Here, we identified Down Syndrome Cell Adhesion Molecule (Dscam) RNA, a molecule involved in neural development and implicated in Down syndrome, bound to FMRP. Elevated Dscam protein levels in Drosophila FMRP null animals and in animals with three copies of the Dscam gene both produced specific and similar synaptic targeting errors in a hard-wired neural circuit which impaired the animal’s sensory perception. Reducing Dscam levels in FMRP null animals reduced synaptic targeting errors and rescued behavioral responses. Our results demonstrate that excess Dscam protein may be a common molecular mechanism underlying altered neural wiring in major causes of intellectual disability.

Down Syndrome Related Muscle Hypotonia: Association with COL6A3 Functional SNP rs2270669

Down syndrome (DS), the principal cause for intellectual disability, is also associated with hormonal, immunological, and gastrointestinal abnormalities. Muscle hypotonia (MH) and congenital heart diseases (CHD) are also frequently observed. Collagen molecules are essential components for maintaining muscle integrity and are formed by the assembly of three chains, alpha 1–3. The type VI collagen is crucial for cardiac as well as skeletal muscles. The COL α1 (VI) and α2 (VI) chains are encoded by genes located at the 21st chromosome and are expected to have higher dosage in individuals with DS. The α 3 (VI) chain is encoded by the COL6A3 located at the chromosome 2. We hypothesized that apart from COL6A1 and COL6A2, COL6A3 may also have some role in the MH of subjects with DS. To find out the relevance of COL6A3 in DS associated MH and CHD, we genotyped two SNPs in COL6A3, rs2270669 and rs2270668, in individuals with DS. Subjects with DS were recruited based on the Diagnostic and Statistical Manual for Mental Disorders-IV and having trisomy of the 21st chromosome. Parents of individuals with DS and ethnically matched controls were enrolled for comparison. Informed written consent was obtained for participation. Peripheral blood was used for isolation of genomic DNA. Target genetic loci were studied by DNA sequence analysis. Data obtained was subjected to population – as well as family-based statistical analysis. rs2270668 was found to be non-polymorphic in the studied population. rs2270669 showed significant association of the “C” allele and “CC” genotype with DS probands having MH (P = 0.02). Computational analysis showed that rs2270669 may induce structural and functional alterations in the COL α3 (VI). Interaction of COLα3 (VI) with different proteins, crucial for muscle integrity, was also noticed by computational methods. This pioneering study on COL6A3 with DS related MH thus indicates that rs2270669 “C” could be considered as a risk factor for DS related MH.

The genomically mosaic brain: aneuploidy and more in neural diversity and disease

Genomically identical cells have long been assumed to comprise the human brain, with post-genomic mechanisms giving rise to its enormous diversity, complexity, and disease susceptibility. However, the identification of neural cells containing somatically generated mosaic aneuploidy - loss and/or gain of chromosomes from a euploid complement - and other genomic variations including LINE1 retrotransposons and regional patterns of DNA content variation (DCV), demonstrate that the brain is genomically heterogeneous. The precise phenotypes and functions produced by genomic mosaicism are not well understood, although the effects of constitutive aberrations, as observed in Down syndrome, implicate roles for defined mosaic genomes relevant to cellular survival, differentiation potential, stem cell biology, and brain organization. Here we discuss genomic mosaicism as a feature of the normal brain as well as a possible factor in the weak or complex genetic linkages observed for many of the most common forms of neurological and psychiatric diseases.

An epigenetic framework for neurodevelopmental disorders: from pathogenesis to potential therapy

Neurodevelopmental disorders (NDDs) are characterized by aberrant and delayed early-life development of the brain, leading to deficits in language, cognition, motor behaviour and other functional domains, often accompanied by somatic symptoms. Environmental factors like perinatal infection, malnutrition and trauma can increase the risk of the heterogeneous, multifactorial and polygenic disorders, autism and schizophrenia. Conversely, discrete genetic anomalies are involved in Down, Rett and Fragile X syndromes, tuberous sclerosis and neurofibromatosis, the less familiar Phelan-McDermid, Sotos, Kleefstra, Coffin-Lowry and "ATRX" syndromes, and the disorders of imprinting, Angelman and Prader-Willi syndromes. NDDs have been termed "synaptopathies" in reference to structural and functional disturbance of synaptic plasticity, several involve abnormal Ras-Kinase signalling ("rasopathies"), and many are characterized by disrupted cerebral connectivity and an imbalance between excitatory and inhibitory transmission. However, at a different level of integration, NDDs are accompanied by aberrant "epigenetic" regulation of processes critical for normal and orderly development of the brain. Epigenetics refers to potentially-heritable (by mitosis and/or meiosis) mechanisms controlling gene expression without changes in DNA sequence. In certain NDDs, prototypical epigenetic processes of DNA methylation and covalent histone marking are impacted. Conversely, others involve anomalies in chromatin-modelling, mRNA splicing/editing, mRNA translation, ribosome biogenesis and/or the regulatory actions of small nucleolar RNAs and micro-RNAs. Since epigenetic mechanisms are modifiable, this raises the hope of novel therapy, though questions remain concerning efficacy and safety. The above issues are critically surveyed in this review, which advocates a broad-based epigenetic framework for understanding and ultimately treating a diverse assemblage of NDDs ("epigenopathies") lying at the interface of genetic, developmental and environmental processes. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

Early-occurring proliferation defects in peripheral tissues of the Ts65Dn mouse model of Down syndrome are associated with patched1 over expression

Down syndrome (DS) is a genetic pathology due to the triplication of human chromosome 21. In addition to mental retardation, individuals with DS exhibit a large range of variable traits, including co-occurring congenital malformations. It is now clear that neurogenesis impairment underlies the typically reduced brain size and, hence, mental retardation in individuals with DS. The small body size and the constellation of congenital malformations in children with DS suggest that proliferation defects may involve peripheral tissues, in addition to the brain. The goal of the current study was to establish whether a generalized impairment of cell proliferation is a key feature of the trisomic condition. We used the Ts65Dn mouse, a widely used DS model, and examined proliferation in tissues with different embryological origin by 5-bromo-2-deoxyuridine immunohistochemistry. We found that 2-day-old (P2) Ts65Dn mice had notably fewer proliferating cells in the heart and liver, and in all proliferating niches of the skin and intestine. A reduced proliferation rate was still present in the intestine at P15. In all tissues, Ts65Dn mice had a similar number of apoptotic cells as euploid mice, indicating no unbalance in cell death. In the skin, liver and intestine of trisomic mice, we found a higher expression of patched1 (Ptch1), a receptor that represses the mitogenic sonic hedgehog (Shh) pathway. This suggests that Ptch1-dependent inhibition of Shh signaling may underlie proliferation impairment in trisomic peripheral tissues. In agreement with the widespread reduction in proliferation, neonate trisomic mice had a reduced body weight and this defect was still present at 30 days of age. Our findings show that, in all examined peripheral tissues, Ts65Dn mice exhibit a notable reduction in proliferation rate, suggesting that proliferation impairment may be a generalized defect of trisomic precursor cells.

Genomic determinants in the phenotypic variability of Down syndrome

Down syndrome caused by trisomy 21 is a collection of phenotypes with variable expressivity and penetrance. The significant advances in exploring the human genome now provide the tools to better understand the contribution of trisomy 21 in the different manifestations of Down syndrome, and the functional links between the genome variability and the phenotypic variability.

Aneuploid human embryonic stem cells: origins and potential for modeling chromosomal disorders

Chromosomal aneuploidies are widely recognized genetic disorders in humans that often lead to spontaneous abortion. Aneuploid fetuses that survive to term commonly exhibit impaired developmental growth and mental retardation in addition to multiple congenital malformations. Preimplantation genetic screening is used to detect chromosomal aneuploidies in early embryos. Human embryonic stem cell (ESC) cell lines generated from aneuploid embryos created a unique repository of cell lines. The spectrum of aneuploidies in these ESC lines reflects the range of common embryonic chromosomal aberrations and significantly differs from the spectrum of aneuploid human ESC lines generated by cell adaptation in culture. The aneuploid human ESC lines represent an excellent model to study human chromosomal abnormalities especially in the early stages of development.

Mitochondrial dysfunction and Down's syndrome: is there a role for coenzyme Q(10) ?

Structural changes and abnormal function of mitochondria have been documented in Down's syndrome (DS) cells, patients, and animal models. DS cells in culture exhibit a wide array of functional mitochondrial abnormalities including reduced mitochondrial membrane potential, reduced ATP production, and decreased oxido-reductase activity. New research has also brought to central stage the prominent role of oxidative stress in this condition. This review focuses on recent advances in the field with a particular emphasis on novel translational approaches involving the utilization of coenzyme Q(10) (CoQ(10) ) to treat a variety of clinical phenotypes associated with DS that are linked to increased oxidative stress and energy deficits. CoQ(10) has already provided promising results in several different conditions associated with altered energy metabolism and oxidative stress in the CNS. Two studies conducted in Ancona investigated the effect of CoQ(10) treatment on DNA damage in DS patients. Although the effect of CoQ(10) was evidenced only at single cell level, the treatment affected the distribution of cells according to their content in oxidized bases. In fact, it produced a strong negative correlation linking cellular CoQ(10) content and the amount of oxidized purines. Results suggest that the effect of CoQ(10) treatment in DS not only reflects antioxidant efficacy, but likely modulates DNA repair mechanisms.

VDR TaqI polymorphism is associated with chronic periodontitis in Italian population

AIM

The aim of this study is to investigate the relationship between a vitamin D receptor polymorphism and the diagnosis of periodontal disease in non-smoker Italian patients with aggressive and chronic periodontitis.

MATERIALS AND METHODS

DNA was obtained from the internal cheek mucosa of 115 patients with chronic periodontitis, 58 with aggressive periodontitis and 65 healthy controls. Allelic discrimination was performed using TaqMan SNP Genotyping Assays. Genotype and allele frequencies were calculated.

RESULTS

Comparisons between diseased patients and healthy controls showed significant differences. Moreover, calculating the odds ratio, individuals with the TT genotype, was more susceptible than individuals with tt to chronic periodontitis and individuals with Tt to aggressive periodontitis. Interestingly, the dominant model (TT + Tt vs. tt) was applicable to chronic periodontitis, whilst for aggressive periodontitis the recessive model (TT vs. Tt + tt) gave the highest odds ratio.

CONCLUSIONS

These data indicated that VDR TaqI polymorphism is differentially associated with development of chronic periodontitis and aggressive periodontitis in Italian population. The study of VDR polymorphisms may therefore be essential for the prevention of periodontitis and for a pre-treatment periodontal and/or for implant assessment. Moreover VDR TaqI polymorphism could be useful to discriminate between aggressive and chronic forms of periodontal disease.

Meta-analysis of heterogeneous Down Syndrome data reveals consistent genome-wide dosage effects related to neurological processes

Background

Down syndrome (DS; trisomy 21) is the most common genetic cause of mental retardation in the human population and key molecular networks dysregulated in DS are still unknown. Many different experimental techniques have been applied to analyse the effects of dosage imbalance at the molecular and phenotypical level, however, currently no integrative approach exists that attempts to extract the common information.

Results

We have performed a statistical meta-analysis from 45 heterogeneous publicly available DS data sets in order to identify consistent dosage effects from these studies. We identified 324 genes with significant genome-wide dosage effects, including well investigated genes like SOD1, APP, RUNX1 and DYRK1A as well as a large proportion of novel genes (N = 62). Furthermore, we characterized these genes using gene ontology, molecular interactions and promoter sequence analysis. In order to judge relevance of the 324 genes for more general cerebral pathologies we used independent publicly available microarry data from brain studies not related with DS and identified a subset of 79 genes with potential impact for neurocognitive processes. All results have been made available through a web server under http://ds-geneminer.molgen.mpg.de/.

Conclusions

Our study represents a comprehensive integrative analysis of heterogeneous data including genome-wide transcript levels in the domain of trisomy 21. The detected dosage effects build a resource for further studies of DS pathology and the development of new therapies.

Molecular diagnosis of Down syndrome using quantitative APEX-2 microarrays

OBJECTIVE

To develop a new rapid and high-throughput microarray-based prenatal diagnostic test for the detection of trisomy 21 (T21).

METHODS

The T21 arrayed primer extension-2 (APEX-2) assay discriminates between trisomy and euploid DNA samples by comparing the signal intensities of allelic fractions of heterozygous single nucleotide polymorphisms (SNPs) after APEX reaction. After preliminary validation using DNA samples from Down syndrome patients, we analyzed DNA samples from cultured and uncultured amniocytes and chorionic villus for 90 SNPs with high heterozygosity from the 21(q21.1q22.2) region. Differences in allelic ratios of heterozygous SNPs in normal and T21 individuals were verified by t-test.

RESULTS

Analysis of the T21 APEX-2 assay results revealed that 90 SNPs were sufficient for reliable discrimination between T21 and euploid DNA samples (P≤0.05 for one or both strands). Using 134 clinical samples from cultured or uncultured fetal cells, both the sensitivity and the specificity of the assay were 100%.

CONCLUSION

Our study provides a proof of principle demonstration of the use of the modified APEX-2 assay as a new, fast and reliable method for prenatal diagnosis of fetal T21.