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PubMed2006

Neuregulin 1 transcripts are differentially expressed in schizophrenia and regulated by 5' SNPs associated with the disease.

Genetic variation in neuregulin 1 (NRG1) is associated with schizophrenia. The disease-associated SNPs are noncoding, and their functional implications remain unknown. We hypothesized that differential expression of the NRG1 gene explains its association to the disease. We examined four of the disease-associated SNPs that make up the original risk haplotype in the 5' upstream region of the gene for their effects on mRNA abundance of NRG1 types I-IV in human postmortem hippocampus. Diagnostic comparisons revealed a 34% increase in type I mRNA in schizophrenia and an interaction of diagnosis and genotype (SNP8NRG221132) on this transcript. Of potentially greater interest, a single SNP within the risk haplotype (SNP8NRG243177) and a 22-kb block of this core haplotype are associated with mRNA expression for the novel type IV isoform in patients and controls. Bioinformatic promoter analyses indicate that both SNPs lead to a gain/loss of putative binding sites for three transcription factors, serum response factor, myelin transcription factor-1, and High Mobility Group Box Protein-1. These data implicate variation in isoform expression as a molecular mechanism for the genetic association of NRG1 with schizophrenia.

Adult↗
PubMed2005

A nano-circular single-stranded DNA as a novel tool for SNPs detection.

Analysis of single nucleotides polymorphisms (SNPs) is very important for the elucidation of gene-based physiological differences. For high-throughput applications, detection systems need to be highly selective, highly sensitive, and simple. In this study, we investigated whether synchronous transcription and translation from nano-circular single-stranded DNA (ssDNA) might be useful for the detection of SNPs. A nano-circular probe ssDNA was designed to contain codons for a (His)6 peptide, and the sense mRNA transcribed from this ssDNA contains a Shine-Dalgarno sequence, a start AUG codon, 6 His codons (CAU), and a stop UAG codon. The entire circular ssDNA is 55 nt and contains T20 as a linker sequence and a binding site for the target SNP-containing DNAs. Our results that show SNPs can be detected by the cell-free synthesis of the (His)6 peptide from this ssDNA. Because this method allows sequence distinction, signal amplification, and easy detection in one system, it should improve the efficacy of high-throughput gene analysis.

Base Pair Mismatch↗
PubMed2006

Genome-wide tagging SNPs with entropy-based Monte Carlo method.

The number of common single nucleotide polymorphisms (SNPs) in the human genome is estimated to be around 3-6 million. It is highly anticipated that the study of SNPs will help provide a means for elucidating the genetic component of complex diseases and variable drug responses. High-throughput technologies such as oligonucleotide arrays have produced enormous amount of SNP data, which creates great challenges in genome-wide disease linkage and association studies. In this paper, we present an adaptation of the cross entropy (CE) method and propose an iterative CE Monte Carlo (CEMC) algorithm for tagging SNP selection. This differs from most of SNP selection algorithms in the literature in that our method is independent of the notion of haplotype block. Thus, the method is applicable to whole genome SNP selection without prior knowledge of block boundaries. We applied this block-free algorithm to three large datasets (two simulated and one real) that are in the order of thousands of SNPs. The successful applications to these large scale datasets demonstrate that CEMC is computationally feasible for whole genome SNP selection. Furthermore, the results show that CEMC is significantly better than random selection, and it also outperformed another block-free selection algorithm for the dataset considered.

Algorithms↗
PubMed2004

Screening of 12 SNPs of CYP3A4 in a Chinese population using oligonucleotide microarray.

Human cytochrome P450 3A4 (CYP34A) plays an important role in the metabolism of many endo- and xenomaterials. It also exhibits a substantial interindividual variation in enzymatic activity. It has been shown that the mutant alleles of CYP3A4 encoding inactive/decreased enzymes are largely caused by single nucleotide polymorphisms (SNPs) in the gene sequence. In the present study, with the goal of detecting the known SNPs of CYP3A4, an oligonucleotide microarray was created. A genotyping standard for this microarray was also established using constructed plasmids as standard templates. The 12 SNPs of CYP3A4 in 387 Chinese DNA samples were screened using this oligonucleotide microarray. Three heterozygous subjects of CYP3A4*/*4, 5 heterozygous subjects of CYP3A4*1/*5, 4 heterozygous subjects of CPY3A4*1/6, and 6 heterozygous subjects of CYP3A4*1/*18 were found. The genotyping results of the 18 heterozygous subjects and 12 wild-type subjects were validated by direct sequencing.

China↗
PubMed2003

Efficient selective screening of haplotype tag SNPs.

UNLABELLED: Haplotypes defined by common single nucleotide polymorphisms (SNPs) have important implications for mapping of disease genes and human traits. Often only a small subset of the SNPs is sufficient to capture the full haplotype information. Such subsets of markers are called haplotype tagging SNPs (htSNPs). Although htSNPs can be identified by eye, efficient computer algorithms and flexible interactive software tools are required for large datasets such as the human genome haplotype map. We describe a java-based program, SNPtagger, which screens for minimal sets of SNP markers to represent given haplotypes according to various user requirements. The program offers several options for inclusion/exclusion of specific markers and presents alternative panels for final selection. AVAILABILITY: The www-based program is available at http://www.well.ox.ac.uk/~xiayi/haplotype/index.html.

Algorithms↗
PubMed2004

CLUSTAG: hierarchical clustering and graph methods for selecting tag SNPs.

UNLABELLED: Cluster and set-cover algorithms are developed to obtain a set of tag single nucleotide polymorphisms (SNPs) that can represent all the known SNPs in a chromosomal region, subject to the constraint that all SNPs must have a squared correlation R2>C with at least one tag SNP, where C is specified by the user. AVAILABILITY: http://hkumath.hku.hk/web/link/CLUSTAG/CLUSTAG.html CONTACT: mng@maths.hku.hk.

Algorithms↗
PubMed2006

A greedier approach for finding tag SNPs.

MOTIVATION: Recent studies have shown that a small subset of Single Nucleotide Polymorphisms (SNPs) (called tag SNPs) is sufficient to capture the haplotype patterns in a high linkage disequilibrium region. To find the minimum set of tag SNPs, exact algorithms for finding the optimal solution could take exponential time. On the other hand, approximation algorithms are more efficient but may fail to find the optimal solution. RESULTS: We propose a hybrid method that combines the ideas of the branch-and-bound method and the greedy algorithm. This method explores larger solution space to obtain a better solution than a traditional greedy algorithm. It also allows the user to adjust the efficiency of the program and quality of solutions. This algorithm has been implemented and tested on a variety of simulated and biological data. The experimental results indicate that our program can find better solutions than previous methods. This approach is quite general since it can be used to adapt other greedy algorithms to solve their corresponding problems. AVAILABILITY: The program is available upon request.

Algorithms↗
PubMed2006

Combining functional and linkage disequilibrium information in the selection of tag SNPs.

UNLABELLED: We have developed an online program, WCLUSTAG, for tag SNP selection that allows the user to specify variable tagging thresholds for different SNPs. Tag SNPs are selected such that a SNP with user-specified tagging threshold C will have a minimum R2 of C with at least one tag SNP. This flexible feature is useful for researchers who wish to prioritize genomic regions or SNPs in an association study. AVAILABILITY: The online WCLUSTAG program is available at http://bioinfo.hku.hk/wclustag/

Algorithms↗
PubMed2006

Search for low penetrance alleles for colorectal cancer through a scan of 1467 non-synonymous SNPs in 2575 cases and 2707 controls with validation by kin-cohort analysis of 14 704 first-degree relatives.

To identify low penetrance susceptibility alleles for colorectal cancer (CRC), we genotyped 1467 non-synonymous SNPs mapping to 871 candidate cancer genes in 2575 cases and 2707 controls. nsSNP selection was biased towards those predicted to be functionally deleterious. One SNP AKAP9 M463I remained significantly associated with CRC risk after stringent adjustment for multiple testing. Further SNPs associated with CRC risk included several previously reported to be associated with cancer risk including ATM F858L [OR=1.48; 95% confidence interval (CI): 1.06-2.07] and P1054R (OR=1.42; 95% CI: 1.14-1.77) and MTHFR A222V (OR=0.82; 95% CI: 0.69-0.97). To validate associations, we performed a kin-cohort analysis on the 14 704 first-degree relatives of cases for each SNP associated at the 5% level in the case-control analysis employing the marginal maximum likelihood method to infer genotypes of relatives. Our observations support the hypothesis that inherited predisposition to CRC is in part mediated through polymorphic variation and identify a number of SNPs defining inter-individual susceptibility. We have made data from this analysis publicly available at http://www.icr.ac.uk/research/research_sections/cancer_genetics/cancer_genetics_teams/molecular_and_population_genetics/software_and_databases/index.shtml in order to facilitate the identification of low penetrance CRC susceptibility alleles through pooled analyses.

Aged↗
PubMed2004

A FRET-based analysis of SNPs without fluorescent probes.

Fluorescence resonance energy transfer (FRET) is a simple procedure for detecting specific DNA sequences, and is therefore used in many fields. However, the cost is relatively high, because FRET-based methods usually require fluorescent probes. We have designed a cost-effective way of using FRET, and developed a novel approach for the genotyping of single nucleotide polymorphisms (SNPs) and allele frequency estimation. The key feature of this method is that it uses a DNA-binding fluorogenic molecule, SYBR Green I, as an energy donor for FRET. In this method, single base extension is performed with dideoxynucleotides labeled with an orange dye and a red dye in the presence of SYBR Green I. The dyes incorporated into the extended products accept energy from SYBR Green I and emit fluorescence. We have validated the method with ten SNPs, which were successfully discriminated by end-point measurements of orange and red fluorescence intensity in a microplate fluorescence reader. Using a mixture of homozygous samples, we also confirmed the potential of this method for estimation of allele frequency. Application of this strategy to large-scale studies will reduce the time and cost of genotyping a vast number of SNPs.

Benzothiazoles↗
PubMed2004

Linkage and association studies of discoidin domain receptor 1 (DDR1) single nucleotide polymorphisms (SNPs) in juvenile oligoarthritis.

OBJECTIVES: Multiple independent juvenile oligoarthritis susceptibility loci have been identified within the major histocompatibility complex (MHC), including HLA-A, HLA-DRB1 and an as yet unlocalized effect in the centromeric class I region. The discoidin domain receptor 1 (DDR1) gene resides within this region and codes for a receptor tyrosine kinase that plays an important role in regulating cell attachment to collagen, chemotaxis, proliferation and matrix metalloproteinase (MMP) production. DDR1 expression in chondrocytes has not been investigated. The objectives of this study were to investigate expression of DDR1 in healthy chondrocytes and to identify linkage and association of this candidate gene with juvenile oligoarthritis. METHODS: A set of 135 simplex juvenile idiopathic arthritis families consisting of one affected child and healthy parent(s) and 199 healthy unrelated individuals were genotyped for six single nucleotide polymorphisms (SNPs) within the DDR1 gene using the primer extension SNaPshot trade mark method. Single-point and multipoint transmission disequilibrium tests were carried out with the ETDT and TDTPHASE packages. Allele frequency comparisons between cases and controls were carried out with the chi(2) test. DDR1 expression was investigated in normal articular cartilage by RT-PCR and immunofluorescence methods. RESULTS: No linkage and association with any of the six SNPs or their haplotypic combinations were observed in the families studied. No significant differences were observed in allele frequencies between patients and controls. DDR1 expression was found in normal articular cartilage by RT-PCR and by immunofluorescence. CONCLUSIONS: The DDR1 SNPs examined are not involved in susceptibility to juvenile oligoarthritis.

Arthritis, Juvenile↗
PubMed2000

Parallel genotyping of human SNPs using generic high-density oligonucleotide tag arrays.

Large scale human genetic studies require technologies for generating millions of genotypes with relative ease but also at a reasonable cost and with high accuracy. We describe a highly parallel method for genotyping single nucleotide polymorphisms (SNPs), using generic high-density oligonucleotide arrays that contain thousands of preselected 20-mer oligonucleotide tags. First, marker-specific primers are used in PCR amplifications of genomic regions containing SNPs. Second, the amplification products are used as templates in single base extension (SBE) reactions using chimeric primers with 3' complementarity to the specific SNP loci and 5' complementarity to specific probes, or tags, synthesized on the array. The SBE primers, terminating one base before the polymorphic site, are extended in the presence of labeled dideoxy NTPs, using a different label for each of the two SNP alleles, and hybridized to the tag array. Third, genotypes are deduced from the fluorescence intensity ratio of the two colors. This approach takes advantage of multiplexed sample preparation, hybridization, and analysis at each stage. We illustrate and test this method by genotyping 44 individuals for 142 human SNPs identified previously in 62 candidate hypertension genes. Because the hybridization results are quantitative, this method can also be used for allele-frequency estimation in pooled DNA samples.

Blood Pressure↗
PubMed2001

Y-chromosomal SNPs in Finno-Ugric-speaking populations analyzed by minisequencing on microarrays.

An increasing number of single nucleotide polymorphisms (SNPs) on the Y chromosome are being identified. To utilize the full potential of the SNP markers in population genetic studies, new genotyping methods with high throughput are required. We describe a microarray system based on the minisequencing single nucleotide primer extension principle for multiplex genotyping of Y-chromosomal SNP markers. The system was applied for screening a panel of 25 Y-chromosomal SNPs in a unique collection of samples representing five Finno--Ugric populations. The specific minisequencing reaction provides 5-fold to infinite discrimination between the Y-chromosomal genotypes, and the microarray format of the system allows parallel and simultaneous analysis of large numbers of SNPs and samples. In addition to the SNP markers, five Y-chromosomal microsatellite loci were typed. Altogether 10,000 genotypes were generated to assess the genetic diversity in these population samples. Six of the 25 SNP markers (M9, Tat, SRY10831, M17, M12, 92R7) were polymorphic in the analyzed populations, yielding six distinct SNP haplotypes. The microsatellite data were used to study the genetic structure of two major SNP haplotypes in the Finns and the Saami in more detail. We found that the most common haplotypes are shared between the Finns and the Saami, and that the SNP haplotypes show regional differences within the Finns and the Saami, which supports the hypothesis of two separate settlement waves to Finland.

Cross-Sectional Studies↗
PubMed2002

Rapid mapping of zebrafish mutations with SNPs and oligonucleotide microarrays.

Large-scale genetic screens in zebrafish have identified thousands of mutations in hundreds of essential genes. The genetic mapping of these mutations is necessary to link DNA sequences to the gene functions defined by mutant phenotypes. Here, we report two advances that will accelerate the mapping of zebrafish mutations: (1) The construction of a first generation single nucleotide polymorphism (SNP) map of the zebrafish genome comprising 2035 SNPs and 178 small insertions/deletions, and (2) the development of a method for mapping mutations in which hundreds of SNPs can be scored in parallel with an oligonucleotide microarray. We have demonstrated the utility of the microarray technique in crosses with haploid and diploid embryos by mapping two known mutations to their previously identified locations. We have also used this approach to localize four previously unmapped mutations. We expect that mapping with SNPs and oligonucleotide microarrays will accelerate the molecular analysis of zebrafish mutations.

Animals↗
PubMed2006

Sickle cell leg ulcers: associations with haemolysis and SNPs in Klotho, TEK and genes of the TGF-beta/BMP pathway.

Cutaneous leg ulcers are common in sickle cell anaemia and their risk might be genetically determined. Sickle cell anaemia patients were studied to examine the relationship of leg ulcers with haemolysis and with single nucleotide polymorphisms (SNPs) in candidate genes that could affect sickle vasoocclusion. Leg ulcer patients had lower haemoglobin levels and higher levels of lactate dehydrogenase, bilirubin, aspartate transaminase and reticulocytes than did control patients with sickle cell anaemia but without leg ulcers. Age-adjusted comparisons showed that sickle cell anaemia-alpha thalassaemia was more frequent among controls than cases. These results strongly suggested that the likelihood of having leg ulcers was related to the intensity of haemolysis. 215 SNPs in more than 100 candidate genes were studied. Associations were found with SNPs in Klotho, TEK and several genes in the TGF-beta/BMP signalling pathway by genotypic association analyses. KL directly or indirectly promotes endothelial nitric oxide (NO) production and the TEK receptor tyrosine kinase is involved in angiogenesis. The TGF-beta/BMP signalling pathway modulates wound healing and angiogenesis, among its other functions. Haemolysis-driven phenotypes, such as leg ulcers, could be improved by agents that reduce sickle erythrocyte density or increase NO bioavailability.

Adult↗
PubMed2006

New SNPs in the IGF2 gene and association between this gene and backfat thickness and lean meat content in Large White pigs.

IGF2-in3-G3072A is a causative mutation for paternally expressed quantitative trait loci on the p arm of porcine chromosome 2 with substantial effect on muscle growth and backfat thickness. The linkage disequilibrium between IGF2-in3-G3072A and IGF2-in7-G162C (IGF2-NciI) in four breeds and associations between these polymorphisms and growth and meat performance in pigs of the Large White breed were analysed. A significant effect of these polymorphisms on backfat thickness and lean meat content was found. In addition, we identified two new single nucleotide polymorphisms (SNPs) in intron 7 of the gene. The existence of complete linkage disequilibrium between IGF2-in3-G3072A locus in the population under study where the locus segregated and SNPs in intron 7 of the IGF2 gene detectable with simple and reliable polymerase chain reaction-restriction fragment length polymorphism techniques (G162C, C179G and G186T) offer possibilities to use these SNPs for genotyping of quantitative trait nucleotide in Large White and Landrace breeds.

Animals↗
PubMed2001

Generation and comparison of EST-derived SSRs and SNPs in barley (Hordeum vulgare L.).

The progress of genome sequencing projects of model plants like barley, combined with the recent advances of high throughput assays, has provided a wealth of sequence information. This information is being employed to develop a high density transcript map of barley (Hordeum vulgare L.). To achieve this goal, the available EST database is being used as a resource for the development of novel microsatellite (SSR) and single nucleotide polymorphism (SNP) markers. So far, a total of 692 microsatellites representing different di-, tri- and tetra-nucleotide repeats were identified from a set of 19,000 EST sequences. Non-redundant SSRs have been used for mapping and so far 76 microsatellite loci were mapped. In addition to the 180 SNP primer pairs, which were designed to target specific ESTs, 72 were polymorphic among the seven genotypes examined here. Of these, 60 SNPs have been mapped applying a denaturing HPLC approach. To examine the potential of the EST-derived markers for pedigree studies, EST-derived SSRs (75 loci) and SNPs (72 loci) were used to fingerprint a set of seven genotypes. The results show that although both marker types yielded similar groupings, a larger data set of both SSRs and SNPs is necessary to obtain stable clusters in unrelated germplasm.

Chromatography, High Pressure Liquid↗
PubMed2004

The reliability of haplotyping inference in nuclear families: misassignment rates for SNPs and microsatellites.

Single nucleotide polymorphisms (SNPs) are widely used when investigators try to map complex disease genes. Although biallelic SNP markers are less informative than microsatellite markers, one can increase their information content by using haplotypes. However, assigning haplotypes (i.e., assigning phase) correctly can be problematic in the presence of SNP heterozygosity. For example, a doubly heterozygous individual, with genotype 12, 12, could have haplotypes 1-1/2-2 or 1-2/2-1 with equal probability; in the absence of additional information, there is no way to determine which haplotype is correct. Thus an algorithm that assigns haplotypes to such an individual will assign the wrong one 50% of the time. We have studied the frequency of haplotype misassignments, i.e., haplotypes that are misassigned solely because of inherent marker ambiguity (not because of errors in genotyping or calculation). We examined both SNPs and microsatellite markers. We used the computer programs GENEHUNTER and SIMWALK to assign the haplotypes. We simulated (a) families with 1-5 children, (b) haplotypes involving different numbers of marker loci (3, 5, 7 and 10 loci, all in linkage equilibrium), and (c) different allele frequencies. Misassignment rates are highest (a) in small families, (b) with many SNP loci, and (c) for loci with the greatest heterozygosity (i.e., where both alleles have frequency 0.5). For example, for triads (i.e., one-child families with both parents genotyped), misassignment rates for SNPs can reach almost 50%. Family sizes of 4-5 children are required in order to ensure a misassignment frequency of < or = 5% for ten-SNP haplotypes with allele frequencies of 0.25-0.5. For microsatellites, a family size of at least 2-3 children is necessary to keep haplotyping misassignments < or = 5%. Finally, we point out that it is misleading for a computer program to yield haplotype assignments without indicating that they may have been misassigned, and we discuss the implications of these misassignments for association and linkage analysis.

Chromosome Mapping↗