Abstract 4909: The role of CpG island methylator phenotype 2 (CIMP2) in early onset colorectal cancer patients

CpG Island Methylator Phenotype (CIMP), characterized by methylation at various promoter sites, has been reported as a subgroup in colorectal cancer. CIMP1 is often associated with microsatellite instability (MSI) as well as BRAF mutation while CIMP negative enriched with P53 mutant. Besides, a CIMP2 classification has also been established and indicated to be associated with KRAS mutation. Most of these experiments related to CIMP were carried out on tumor samples from late onset patients with a mean or median age of at least 60. Thus it was of interest to observe any deviation of such pattern among early onset colorectal cancer population. Bisulfite conversion of the extracted DNA from 73 tumor samples with MSS status were examined via pyrosequence for their methylation status among loci MINT1, MINT2 and MINT27, the most frequently methylated sites reported in CIMP 2 phenomenon. These samples were free from MLH1 methylation and BRAF mutation to exclude conditions of CIMP1. The age group ranged from 29 to 68 years old with a mean age of 50.7 years old. Sequencing of its genomic DNA for KRas mutation was also screened as per se to previous studies. It was found that CIMP2 appeared more frequently in patients over the age of 50 (p=0.04) when compared with patients below 50 years old. Furthermore, methylation of the CIMP 2 loci examined (MINT1, MINT2 and MINT27) were most likely accompanied with the mutation of KRas in patients over 50 years old (p=0.05) while there was no observed correlation of CIMP 2 loci and KRas mutation in patient samples under 50 years of age. Since the CIMP2 phenotype is not seen in early-onset CRC samples, our data suggests that an alternative pathway, but not CIMP, may be responsible for the tumorigenesis of early-onset MSS CRC. Moreover, current studies proposed chromosomal instability may be a distinct mechanism in the pathogenesis of CRC, thus investigation would be carried on this aspect.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4909.

Experimental investigation on regulated and unregulated emissions of a diesel/methanol compound combustion engine with and without diesel oxidation catalyst

The use of methanol in combination with diesel fuel is an effective measure to reduce particulate matter (PM) and nitrogen oxides (NOx) emissions from in-use diesel vehicles. In this study, a diesel/methanol compound combustion (DMCC) scheme was proposed and a 4-cylinder naturally-aspirated direct-injection diesel engine modified to operate on the proposed combustion scheme. The effect of DMCC and diesel oxidation catalyst (DOC) on the regulated emissions of total hydrocarbons (THC), carbon monoxide (CO), NOx and PM was investigated based on the Japanese 13 Mode test cycle. Certain unregulated emissions, including methane, ethyne, ethene, 1,3-butadiene, BTX (benzene, toluene, xylene), unburned methanol and formaldehyde were also evaluated based on the same test cycle. In addition, the soluble organic fraction (SOF) in the particulate and the particulate number concentration and size distribution were investigated at certain selected modes of operation. The results show that the DMCC scheme can effectively reduce NOx, particulate mass and number concentrations, ethyne, ethene and 1,3-butadiene emissions but significantly increase the emissions of THC, CO, NO(2), BTX, unburned methanol, formaldehyde, and the proportion of SOF in the particles. After the DOC, the emission of THC, CO, NO(2), as well as the unregulated gaseous emissions, can be significantly reduced when the exhaust gas temperature is sufficiently high while the particulate mass concentration is further reduced due to oxidation of the SOF.

Emission reduction from diesel engine using fumigation methanol and diesel oxidation catalyst

This study is aimed to investigate the combined application of fumigation methanol and a diesel oxidation catalyst for reducing emissions of an in-use diesel engine. Experiments were performed on a 4-cylinder naturally-aspirated direct-injection diesel engine operating at a constant speed of 1800 rev/min for five engine loads. The experimental results show that at low engine loads, the brake thermal efficiency decreases with increase in fumigation methanol; but at high loads, it slightly increases with increase in fumigation methanol. The fumigation method results in a significant increase in hydrocarbon (HC), carbon monoxide (CO), and nitrogen dioxide (NO(2)) emissions, but decrease in nitrogen oxides (NO(x)), smoke opacity and the particulate mass concentration. For the submicron particles, the total number of particles decreases. In all cases, there is little change in geometrical mean diameter of the particles. After catalytic conversion, the HC, CO, NO(2), particulate mass and particulate number concentrations were significantly reduced at medium to high engine loads; while the geometrical mean diameter of the particles becomes larger. Thus, the combined use of fumigation methanol and diesel oxidation catalyst leads to a reduction of HC, CO, NO(x), particulate mass and particulate number concentrations at medium to high engine loads.

Frequent inactivation of axon guidance molecule RGMA in human colon cancer through genetic and epigenetic mechanisms

BACKGROUND & AIMS

Repulsive guidance molecule member A (RGMA) is a glycosylphosphatidylinositol-anchored glycoprotein and axon guidance molecule that signals through its receptor, neogenin (NEO1), a homologue of the deleted-in-colorectal cancer (DCC) gene. RGMA also functions as a bone morphogenetic protein (BMP) coreceptor. We studied the potential roles of RGMA and NEO1 in colorectal cancer (CRC) pathogenesis.

METHODS

We analyzed expression of RGMA and NEO1, as well as their epigenetic and genetic changes, in a large series of CRC samples, normal colon tissues, adenomas, and cell lines. These studies were accompanied by in vitro functional assay.

RESULTS

RGMA and NEO1 expression were significantly down-regulated in most CRCs, adenomas, and cell lines. RGMA was frequently silenced by promoter methylation in CRCs (86.7%), adenomas (90.9%), and CRC cell lines (92.3%) but not in normal colon tissues; allelic imbalance of RGMA and NEO1 was observed in 40% and 49% of CRCs, respectively. In CRC samples, reduced RGMA levels were significantly associated with mismatch repair deficiency or mutations in KRAS or BRAF. Exposure to 5-aza-2'-deoxycytidine restored RGMA expression in CRC cell lines. Transfection of RGMA into CRC cells suppressed cell proliferation, migration, and invasion and also increased apoptosis in response to DNA-damaging agent.

CONCLUSIONS

The frequent genetic and epigenetic inactivation of RGMA in CRCs and adenomas along with its in vitro function collectively support its role as a tumor suppressor in colon cells. These findings add to the expanding list of axon guidance molecules with disrupted function during colon carcinogenesis and create new opportunities for early detection and drug development.

Heritable somatic methylation and inactivation of MSH2 in families with Lynch syndrome due to deletion of the 3' exons of TACSTD1

Lynch syndrome patients are susceptible to colorectal and endometrial cancers owing to inactivating germline mutations in mismatch repair genes, including MSH2 (ref. 1). Here we describe patients from Dutch and Chinese families with MSH2-deficient tumors carrying heterozygous germline deletions of the last exons of TACSTD1, a gene directly upstream of MSH2 encoding Ep-CAM. Due to these deletions, transcription of TACSTD1 extends into MSH2. The MSH2 promoter in cis with the deletion is methylated in Ep-CAM positive but not in Ep-CAM negative normal tissues, thus revealing a correlation between activity of the mutated TACSTD1 allele and epigenetic inactivation of the corresponding MSH2 allele. Gene silencing by transcriptional read-through of a neighboring gene in either sense, as demonstrated here, or antisense direction, could represent a general mutational mechanism. Depending on the expression pattern of the neighboring gene that lacks its normal polyadenylation signal, this may cause either generalized or mosaic patterns of epigenetic inactivation.

Epigenetic-genetic interactions in the APC/WNT, RAS/RAF, and P53 pathways in colorectal carcinoma

PURPOSE

Early events in colorectal tumorigenesis include mutation of the adenomatous polyposis coli (APC) gene and epigenetic hypermethylation with transcriptional silencing of the O(6)-methylguanine DNA methyltransferase (MGMT), human mut L homologue 1 (hMLH1), and P16/CDKN2A genes. Epigenetic alterations affect genetic events: Loss of MGMT via hypermethylation reportedly predisposes to guanine-to-adenine or cytosine-to-thymine (G:C-->A:T) transition mutations in KRAS and P53, and silencing of hMLH1 leads to high levels of microsatellite instability (MSI-H)/mutator phenotype, suggesting that epigenetic-genetic subtypes exist.

EXPERIMENTAL DESIGN

We evaluated the relationships of aberrant methylation of APC, MGMT, hMLH1, P16, N33, and five MINTs to mutations in APC, KRAS, BRAF, and P53 in 208 colorectal carcinomas.

RESULTS

We found that APC hypermethylation was age related (P = 0.04), in contrast to the other genes, and did not cluster with CpG island methylator phenotype (CIMP) markers. Hypermethylation of APC concurrently with either MGMT or hMLH1 was strongly associated with occurrence of G-to-A transitions in APC [odds ratio (OR), 26.8; P < 0.0002 from multivariable logic regression model], but C-to-T transitions had no associations. There was no relationship of hypermethylation of any gene, including MGMT, with G-to-A or C-to-T transitions in KRAS or P53, although APC hypermethylation was associated with P53 mutation (P < 0.0002). CIMP with MSI-H due to hMLH1 hypermethylation, or CIMP with loss of MGMT expression in non-MSI-H tumors, was associated with BRAF mutation (OR, 4.5; P < 0.0002). CIMP was also associated with BRAF V600E T-to-A transversion (OR, 48.5; P < 0.0002).

CONCLUSIONS

Our findings suggest that the heterogeneous epigenetic dysregulation of promoter methylation in various genes is interrelated with the occurrence of mutations, as manifested in epigenetic-genetic subgroups of tumors.

MicroRNA expression profiles associated with prognosis and therapeutic outcome in colon adenocarcinoma

CONTEXT

MicroRNAs have potential as diagnostic biomarkers and therapeutic targets in cancer. No study has evaluated the association between microRNA expression patterns and colon cancer prognosis or therapeutic outcome.

OBJECTIVE

To identify microRNA expression patterns associated with colon adenocarcinomas, prognosis, or therapeutic outcome.

DESIGN, SETTING, AND PATIENTS

MicroRNA microarray expression profiling of tumors and paired nontumorous tissues was performed on a US test cohort of 84 patients with incident colon adenocarcinoma, recruited between 1993 and 2002. We evaluated associations with tumor status, TNM staging, survival prognosis, and response to adjuvant chemotherapy. Associations were validated in a second, independent Chinese cohort of 113 patients recruited between 1991 and 2000, using quantitative reverse transcription polymerase chain reaction assays. The final date of follow-up was December 31, 2005, for the Maryland cohort and August 16, 2004, for the Hong Kong cohort.

MAIN OUTCOME MEASURES

MicroRNAs that were differentially expressed in tumors and microRNA expression patterns associated with survival using cancer-specific death as the end point. RESULTS Thirty-seven microRNAs were differentially expressed in tumors from the test cohort. Selected for validation were miR-20a, miR-21, miR-106a, miR-181b, and miR-203, and all 5 were enriched in tumors from the validation cohort (P < .001). Higher miR-21 expression was present in adenomas (P = .006) and in tumors with more advanced TNM staging (P < .001). In situ hybridization demonstrated miR-21 to be expressed at high levels in colonic carcinoma cells. The 5-year cancer-specific survival rate was 57.5% for the Maryland cohort and was 49.5% for the Hong Kong cohort. High miR-21 expression was associated with poor survival in both the training (hazard ratio, 2.5; 95% confidence interval, 1.2-5.2) and validation cohorts (hazard ratio, 2.4; 95% confidence interval, 1.4-3.9), independent of clinical covariates, including TNM staging, and was associated with a poor therapeutic outcome.

CONCLUSIONS

Expression patterns of microRNAs are systematically altered in colon adenocarcinomas. High miR-21 expression is associated with poor survival and poor therapeutic outcome.

Experimental investigation on the performance, gaseous and particulate emissions of a methanol fumigated diesel engine

Experiments were conducted on a 4-cylinder direct-injection diesel engine with fumigation methanol injected into the air intake of each cylinder. The fumigation methanol was injected to top up 10%, 20% and 30% of the power output under different engine operating conditions. The effects of fumigation methanol on engine performance, gaseous emissions and particulate emission were investigated. The experimental results show that there is a decrease in the brake thermal efficiency when fumigation methanol is applied, except at the highest load of 0.67 MPa. At low loads, the brake thermal efficiency decreases with increase in fumigation methanol; but at high loads, it increases with increase in fumigation methanol. The fumigation method results in a significant increase in hydrocarbon (HC), carbon monoxide (CO), and nitrogen dioxide (NO(2)) emissions. The concentration of nitrogen oxides (NOx) is significantly reduced except at close to full load condition. There is also a reduction in the smoke opacity and the particulate matter (PM) mass concentration. For the submicron particles, the total number of particles decreases at low and medium loads but increases at high loads. In all cases, there is a shift of the particles towards smaller geometrical mean diameter, especially at high loads. The increase in nano-sized particles and the increase in NO(2) emission could have serious impact on human health.

Gene expression patterns of human colon tops and basal crypts and BMP antagonists as intestinal stem cell niche factors

Human colonic epithelial cell renewal, proliferation, and differentiation are stringently controlled by numerous regulatory pathways. To identify genetic programs of human colonic epithelial cell differentiation in vivo as well as candidate marker genes that define colonic epithelial stem/progenitor cells and the stem cell niche, we applied gene expression analysis of normal human colon tops and basal crypts by using expression microarrays with 30,000 genes. Nine hundred and sixty-nine cDNA clones were found to be differentially expressed between human colon crypts and tops. Pathway analysis revealed the differential expression of genes involved in cell cycle maintenance and apoptosis, as well as genes in bone morphogenetic protein (BMP), Notch, Wnt, EPH, and MYC signaling pathways. BMP antagonists gremlin 1, gremlin 2, and chordin-like 1 were found to be expressed by colon crypts. In situ hybridization and RT-PCR confirmed that these BMP antagonists are expressed by intestinal cryptal myofibroblasts and smooth muscle cells at the colon crypt. In vitro analysis demonstrated that gremlin 1 partially inhibits Caco-2 cell differentiation upon confluence and activates Wnt signaling in normal rat intestinal epithelial cells. Collectively, the expression data set provides a comprehensive picture of human colonic epithelial cell differentiation. Our study also suggests that BMP antagonists are candidate signaling components that make up the intestinal epithelial stem cell niche.

Microsatellite instability and novel mismatch repair gene mutations in northern Chinese population with hereditary non-polyposis colorectal cancer

OBJECTIVE

Hereditary non-polyposis colorectal cancer (HNPCC) syndrome is the most common cause of hereditary colorectal cancer with an early age of onset. Microsatellite instability (MSI) and germline mutation in one of the DNA mismatch repair (MMR) genes are found in the majority of HNPCC families and provide an opportunity for genetic diagnosis and prophylactic screening. The MMR gene mutation spectrum may vary across different populations and be influenced by founder mutations that prevail in specific ethnic groups. China is a big and ancient nation with enormous genetic diversity, which is especially notable between the northern and southern Chinese populations. A MMR gene mutation database for the southern Chinese population based in Hong Kong has been previously established. This study compares the MMR gene mutation spectrum and the MSI of HNPCC between the northern and southern Chinese populations.

METHODS

Twenty-five HNPCC families from northern China were systematically analyzed. The MSI analysis was performed using five loci in the USA National Cancer Institute (NCI) panel (D2S123, D5S346, BAT-25, BAT-26 and BAT-40) by PCR from the tumor and normal tissue. MSH2, MSH6 and MLH1 were performed using immunohistochemical staining. Two founder mutations of MSH2 and MLH1 were examined by PCR base analyses using primers flanking the two deletion sites (c.1452_1455delAATG in MSH2 and 1.8 kb deletion involving exon 11 of MLH1).

RESULTS

Of the 25 families collected, 19 met Bethesda guideline (BG) 1 and six met BG3. Twenty-two (15.7%) were extra-colonic cancers with gastric cancer (in seven patients) being the most common cancer type. Of the 25 tumors analyzed, 21 (84%) were high level microsatellite instability (MSI-H) and four (16%) were microsatellite stable (MSS). Eighteen (86%) of the 21 MSI-H tumors showed loss of either the MLH1 or the MSH2 protein. Three MSI-H tumors and all four MSS tumors showed no loss of expression of the three MMR proteins. Out of the 21 patients with MSI-H tumors, 12 (57%) showed pathogenic germline mutations in either MLH1 (n = 8) or MSH2 (n = 4). Overall, three novel mutations (in patients H22, H17 and H29) have been identified. One of them, c.503_4insA, caused a frameshift mutation in the MLH1 gene. The other two were found in the MSH2 gene, including a frameshift (c.899_890insAT) and a splice junction (IVS7-1G-->A, SA of Exon 8) mutation.

CONCLUSIONS

The results suggest a distinctly different mutation spectrum of MMR genes between northern and southern Chinese populations and call for a systematic, nationwide study to facilitate the design of a MMR gene mutation detection strategy tailored for individual populations in China.

[Experimental study on ultrafine particle characteristics exhausted from various fuelled vehicles]

The fine particle size distribution characteristics obtained from a diesel taxi, a diesel light bus, a gasoline private car and a liquefied petroleum gas (LPG) fuelled taxi were carried out on a chassis dynamometer system. The measurements were performed at different driving modes, i.e. , with low and high idling and from 10 kmxh(-1) to 70 kmxh(-1), 4 cruise operations using the instrument SMPS for collecting particles of 0.015-0.7microm diameter in range. It was found that different fuelled vehicles and different driving modes characterize considerable differences in size number and mass concentration distributions. Diesel vehicles contribute much more nuclei and accumulation mode particles of 30 - 150 nm, while LPG and gasoline fuelled vehicles exhaust much more nuclei mode particles of 15-30 nm. Overall, diesel-fuelled vehicles exhaust much more particles number and mass than gasoline and LPG fuelled vehicles; In the present study, diesel vehicles exhaust the ranges of total SMPS particle number, mass concentration with (0.3-3.6) x 10(8) number x cm(-3), 0.03 - 0.6 microg cm(- 3) respectively, and gasoline and LPG fuelled vehicles exhaust 2.3 x 10(4) - 1.2 x 10(7) number x cm(-3), 8 x 10(-5)-0.1 microgxcm(-3); 8.2 x 10(3)8.8 x 10(6) number x cm(-3), 1.7 x 10(-5) -0.09 microg x cm(-3), respectively; For all types of vehicles, the particle number and mass concentrations are small at low-idle and low-speed-driving modes, and are large at high-idle and high-speed-driving modes. They generally increase with the vehicle speed increasing from 10 to 70 kmx h(-1).

Heritable germline epimutation of MSH2 in a family with hereditary nonpolyposis colorectal cancer

Epimutations in the germline, such as methylation of the MLH1 gene, may contribute to hereditary cancer syndrome in human, but their transmission to offspring has never been documented. Here we report a family with inheritance, in three successive generations, of germline allele-specific and mosaic hypermethylation of the MSH2 gene, without evidence of DNA mismatch repair gene mutation. Three siblings carrying the germline methylation developed early-onset colorectal or endometrial cancers, all with microsatellite instability and MSH2 protein loss. Clonal bisulfite sequencing and pyrosequencing showed different methylation levels in different somatic tissues, with the highest level recorded in rectal mucosa and colon cancer tissue, and the lowest in blood leukocytes. This mosaic state of germline methylation with different tissue distribution could act as the first hit and provide a mechanism for genetic disease inheritance that may deviate from the mendelian pattern and be overlooked in conventional leukocyte-based genetic diagnosis strategy.

Recurrent KRAS codon 146 mutations in human colorectal cancer

An activating point mutation in codon 12 of the HRAS gene was the first somatic point mutation identified in a human cancer and established the role of somatic mutations as the common driver of oncogenesis. Since then, there have been over 11,000 mutations in the three RAS (HRAS, KRAS and NRAS) genes in codons 12, 13 and 61 reported in the literature. We report here the identification of recurrent somatic missense mutations at alanine 146, a highly conserved residue in the guanine nucleotide binding domain. In two independent series of colorectal cancers from Hong Kong and the United States we detected KRAS A146 mutations in 7/126 and 2/94 cases, respectively, giving a combined frequency of 4%. We also detected KRAS A146 mutations in 2/40 (5%) colorectal cell lines, including the NCI-60 colorectal cancer line HCC2998. Codon 146 mutations thus are likely to make an equal or greater contribution to colorectal cancer than codon 61 mutations (4.2% in our combined series, 1% in the literature). Lung adenocarcinomas and large cell carcinomas did not show codon 146 mutations. We did, however, identify a KRAS A146 mutation in the ML-2 acute myeloid leukemia cell line and an NRAS A146 mutation in the NALM-6 B-cell acute lymphoblastic leukemia line, suggesting that the contribution of codon 146 mutations is not entirely restricted to colorectal cancers or to KRAS.

BRAF and NRAS mutations are uncommon in melanomas arising in diverse internal organs

BACKGROUND

Malignant melanoma arising from different body compartments may be associated with differing aetiological factors and clinical behaviour, and may manifest diverse molecular genetic profiles. Although many studies have focused on cutaneous melanoma, little is known of mucosal and other types of melanoma. In particular, malignant melanoma of soft parts is different from other melanomas in many respects, yet manifests a common melanocytic differentiation. Mutation of BRAF is now known to be common in cutaneous melanomas, and raises possible new therapeutic options of anti-RAF treatment for these patients. Few data are available for non-cutaneous melanomas.

AIMS

To study the incidence of BRAF and NRAS mutations in melanomas arising in diverse internal organs.

METHODS

Fifty one melanomas from various internal organs were investigated for BRAF and NRAS mutation by direct DNA sequencing.

RESULTS

BRAF and NRAS mutations were found in two and five mucosal melanomas arising from the aerodigestive and female genital tracts (n = 36). Their occurrence is mutually exclusive, giving a combined mutation incidence rate of 19.4% in mucosal melanomas. Both BRAF and NRAS mutations were absent in malignant melanoma of soft parts (n = 7). BRAF mutation was also absent in uveal melanoma (n = 6), but was seen in two of five cutaneous melanomas. The incidence of BRAF or combined BRAF/NRAS mutations in all non-cutaneous groups was significantly lower than published rates for cutaneous melanomas.

CONCLUSION

Each melanoma subtype may have a unique oncogenetic pathway of tumour development, and only a small fraction of non-cutaneous melanomas may benefit from anti-RAF treatment.

Mutations of PIK3CA in gastric adenocarcinoma

Background

Activation of the phosphatidylinositol 3-kinase (PI3K) through mutational inactivation of PTEN tumour suppressor gene is common in diverse cancer types, but rarely reported in gastric cancer. Recently, mutations in PIK3CA, which encodes the p110α catalytic subunit of PI3K, have been identified in various human cancers, including 3 of 12 gastric cancers. Eighty percent of these reported mutations clustered within 2 regions involving the helical and kinase domains. In vitro study on one of the "hot-spot" mutants has demonstrated it as an activating mutation.

Methods

Based on these data, we initiated PIK3CA mutation screening in 94 human gastric cancers by direct sequencing of the gene regions in which 80% of all the known PIK3CA mutations were found. We also examined PIK3CA expression level by extracting data from the previous large-scale gene expression profiling study. Using Significance Analysis of Microarrays (SAM), we further searched for genes that show correlating expression with PIK3CA.

Results

We have identified PIK3CA mutations in 4 cases (4.3%), all involving the previously reported hotspots. Among these 4 cases, 3 tumours demonstrated microsatellite instability and 2 tumours harboured concurrent KRAS mutation. Data extracted from microarray studies showed an increased expression of PIK3CA in gastric cancers when compared with the non-neoplastic gastric mucosae (p < 0.001). SAM further identified 2910 genes whose expression levels were positively associated with that of PIK3CA.

Conclusion

Our data suggested that activation of the PI3K signalling pathway in gastric cancer may be achieved through up-regulation or mutation of PIK3CA, in which the latter may be a consequence of mismatch repair deficiency.

MSH2 c.1452-1455delAATG is a founder mutation and an important cause of hereditary nonpolyposis colorectal cancer in the southern Chinese population

Hereditary nonpolyposis colorectal cancer (HNPCC) accounts for approximately 2% of all colorectal cancer (CRC) cases and is the most common hereditary CRC syndrome. We have previously reported a high incidence of microsatellite instability (MSI) and germline mismatch repair (MMR) gene mutations in young Hong Kong Chinese with CRC. Ongoing studies at the Hereditary Gastrointestinal Cancer Registry in Hong Kong have revealed a unique germline MSH2 c.1452-1455delAATG mutation that has not been reported in other ethnic groups. Detailed analysis showed that this specific MSH2 mutation constituted 21% of all germline MMR gene mutations and 36% of all MSH2 germline mutations identified. We designed a specific PCR-based diagnostic test on paraffin-embedded tissues and identified this germline mutation in 2 (1.5%) of 138 consecutive patients with early-onset CRC (<46 years of age at diagnosis). Haplotype analysis was performed using 11 microsatellite markers located between D2S391 and D2S123. All 10 families had the same disease haplotype, suggesting a founder effect. These 10 families all originated from the Chinese province of Guangdong, which historically included Hong Kong. It is the most populous of the Chinese provinces, with a population of >93 million. Further analysis suggested that this founder mutation may date back to between 22 and 103 generations ago. The identification of this MSH2 founder mutation has important implications for the design of mutation-detection strategies for the southern Chinese population. Since there were major emigrations from Hong Kong and Guangdong province during the 19th and 20th centuries, this finding is also significant for Chinese communities worldwide.

Downregulation of ID4 by promoter hypermethylation in gastric adenocarcinoma

Promoter hypermethylation has become apparent as a common mechanism of gene silencing in cancer. Based on our published microarray expression data, we noticed a prominent downregulation of ID4 in gastric adenocarcinoma. The dense 5' CpG island covering the previously mapped upstream promoter of ID4 has prompted us to relate its downregulation to promoter hypermethylation. ID proteins are distinct members in the helix-loop-helix family of transcriptional regulators, which modulate various key developmental processes. Emerging data have suggested the involvement of ID genes in tumorigenesis. In this study using bisulfite genomic sequencing, we have found hypermethylation of ID4 promoter in most gastric cancer cell lines and 30% of primary tumors. This correlated with decreased level of ID4 expression. Restoration of ID4 expression in various gastric cancer cell lines was achieved by treatment with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine, which at times required the synergistic action of the histone deacetylase inhibitor trichostatin A, but not with trichostatin A alone. Re-expression was accompanied by the corresponding ID4 promoter demethylation. Furthermore, we have found significant association of ID4 promoter methylation with hMLH1 promoter methylation (P=0.008) and microsatellite instability (P=0.006). Overall, our results have shown that transcriptional silencing of ID4 is related to the aberrant methylation of its promoter in gastric cancer. The significant association of ID4 and hMLH1 promoter hypermethylation suggested that ID4 may also be among the genes being targeted in the CpG island methylator phenotype tumorigenic pathway.

Paediatric utilization of a general emergency department in a developing country

AIM

Knowledge of the spectrum and frequencies of pediatric emergencies presenting to an emergency department (ED) of individual developing countries is vital in optimizing the quality of care delivered locally.

METHODS

A prospective 6 wk review of all pediatric (< 18 y) attendees to an urban ED was done, with patient age, presenting complaints, diagnoses, time of arrival and disposition recorded.

RESULTS

Complete data were available on 1172 patients, with an age range of 4 d to 18 y (mean +/- SD 6.9 +/- 5.6 y); 43% were aged < or = 4 y. The main presenting complaints were injuries (26.9%), fever (24%) and breathing difficulties (16.6%). The most common diagnosis was minor trauma (24.2%), with soft-tissue injuries predominating (80.6%). The other diagnoses were asthma (12.6%), upper respiratory infections (12.1%), other infections (12.1%) and gastroenteritis (11.8%). Equal proportions of patients were seen throughout the day. 25% of patients were admitted. Young age (< 1 y); presence of past medical history, general practitioner referrals, diagnosis of bronchiolitis and pneumonia were significantly associated with risk of admission.

CONCLUSION

A wide spectrum of paediatric illnesses was seen in the ED, with an overrepresentation of young children. This supports the decision to have either a separate pediatric ED or paediatric residents on the staff. The training curricula should emphasize the management of pediatric trauma, infections and asthma. Alternatively, developing guidelines for the five most common presenting complaints would account for 82% of all attendees and could be directed towards all staff on the ED.

Germline, somatic and epigenetic events underlying mismatch repair deficiency in colorectal and HNPCC-related cancers

High-frequency microsatellite instability (MSI-H) results from deficiency in nucleotide mismatch repair. It contributes significantly to carcinogenesis in the human colorectal mucosa. Here we study 41 colorectal and three other HNPCC-related cancers with MSI-H to provide comprehensive information on the mechanisms of inactivation of the two major proteins involved, hMLH1 and hMSH2. Seventeen of the patients had family histories meeting the criteria for Bethesda grades 1, 2 or 3. Of these familial cases, 14 (83%) had early-onset disease, defined on the basis of diagnosis prior to the age of 50, but in three the disease was of late onset (>50 years). A second subset of 20 patients had early onset disease without family history. The remaining seven patients were selected to allow comparisons with sporadic, late-onset disease, the molecular basis of which has been extensively reported elsewhere. We stratified the tumours initially on the basis of hMLH1 or hMSH2 protein deficiency, detected by immunohistochemistry, and then by analysis of germline and somatic mutation, mRNA transcription, loss of heterozygosity (LOH) at the hMLH1 and hMSH2 loci, and methylation status in two regions of the hMLH1 promoter. The functional significance of several of these changes in the MSI-H tumours was confirmed by comparisons with 16 tumours with low-frequency microsatellite instability and 56 tumours with stable microsatellites. As anticipated, patients with family histories usually showed germline mutation of hMSH2 or hMLH1. In many cases the residual normal allele was silenced in their tumours by loss of heterozygosity (LOH). The small subset of late-onset, sporadic cases confirmed the preponderance in this group of biallelic hMLH1 promoter methylation. In the early-onset, apparently sporadic subset there were 11 tumours with hMLH1 deficiency, five with hMSH2 deficiency and four with no detectable abnormality in expression of either protein. These showed a complex mixture of lesions, including germline and somatic mutations, promoter methylation, LOH, suppression of wild-type RNA by as yet undiscovered mechanisms, or no detectable abnormality in any of these parameters. Evidence is presented to indicate that methylation in proximal region of the hMLH1 promoter is a more reliable correlate of transcriptional silencing in colorectal cancers than methylation in upstream region. These observations have significant implications for management of patients with MSI-H tumours.

Discrimination of an infected brain tumor from a cerebral abscess by combined MR perfusion and diffusion imaging

The aim of this study was to investigate the signal characteristics of the abscess wall and tumor wall on diffusion-weighted and perfusion-weighted images and thus to evaluate the feasibility of using combined MR diffusion and perfusion imaging to differentiate pyogenic cerebral abscess from infected brain tumor. The tumor wall of various types of cystic or necrotic brain tumor was significantly hyperintense relative to that of cerebral abscess wall on both diffusion-weighted images and regional cerebral blood volume maps. Sixteen patients who had cerebral masses with large cystic or necrotic cavities were imaged to generate diffusion-weighted images and regional cerebral blood volume maps using single-shot echoplanar imaging (EPI) pulse sequences. Apart from qualitative analysis, apparent diffusion coefficients (ADC) as well as regional cerebral blood volume (rCBV) ratios were calculated from the abscess wall and peripheral tumor wall and comparison was made by using Student's t-test. The tumor wall of various types of cystic or necrotic brain tumor had significantly lower ADCs relative to those of the abscess wall (P<0.005) and thus appeared relatively hyperintense on diffusion-weighted images. The mean rCBV ratio relative to normal white matter (2.90+/-0.62) of the peripheral tumor wall of various types of cystic or necrotic brain tumor were significantly larger than the mean rCBV ratio (0.45+/-0.11) of the pyogenic cerebral abscess wall (P<0.001) by Student's t-test. It is concluded that the combined MR diffusion and perfusion imaging might be capable of differentiating an infected brain tumor from a pyogenic cerebral abscess.

Acquired immunodeficiency syndrome presenting as childhood non-Hodgkin's lymphoma

Two children with non-Hodgkin's lymphoma (NHL) as the presenting illness of acquired immunodeficiency syndrome (AIDS) are described. There was a delay in diagnosing the underlying AIDS in both cases. In the first case, an 18-month-old boy with stage IV, high-grade,T-cell NHL, the diagnosis of underlying AIDS was suspected only when he developed recurrent and profound opportunistic infection during chemotherapy. The second case, an eight-month-old female infant presented initially with hepatosplenomegaly and thrombocytopenia of undetermined cause. She had progressive abdominal distension and swelling of her right eye one year later due to high grade B-cell NHL. She was later found to be sero-positive for HIV during pre-chemotherapy screening. As the prevalence of HIV infection continues to increase, HIV infection should be considered in the differential diagnoses of childhood hepatosplenomegaly and thrombocytopenia, and as a possible underlying cause of childhood cancer, especially NHL.

Bipolar cell diversity in the primate retina: morphologic and immunocytochemical analysis of a new world monkey, the marmoset Callithrix jacchus

The aim of this study was to identify the bipolar cell types in the retina of a New World monkey, the common marmoset, and compare them with those found in the Old World macaque monkey. Retinal whole-mounts, sections, or both, were stained by using DiI labeling and immunohistochemical methods. Semithin sections were analyzed by using quantitative methods. We show that the same morphologic types of bipolar cell as described for the Old World macaque monkey by Boycott and Wässle (Boycott and Wässle [1991] Eur. J. Neurosci. 3:1069-1088) are present in marmoset retina: two types of midget bipolar cells, six type of diffuse bipolar cells, a blue cone bipolar cell, and one type of rod bipolar cell. The pattern of staining with different immunohistochemical markers ("fingerprint") of each bipolar cell type in marmoset was also the same as described for macaque, with one exception: the flat midget bipolar cell (FMB) class is labeled by antibodies to recoverin in macaque but is labeled by antibodies to CD15 in marmoset. The labeled FMB cells in marmoset make contact with multiple cone photoreceptors throughout most of the extrafoveal retina. The spatial density of bipolar cells in marmoset is shown to be sufficient to support one-to-one connectivity of midget bipolar and ganglion cells in the fovea and to allow for parallel pathways to ganglion cells throughout the retina. Quantitative differences in the morphology and receptor connectivity between marmoset and macaque can be related to differences in cone and rod photoreceptor density between the species. We conclude that bipolar cell diversity is a preserved feature of the primate retina.

Early-onset colorectal cancer with stable microsatellite DNA and near-diploid chromosomes

Colorectal cancer has been described in terms of genetic instability selectively affecting either microsatellite sequences (MIN) or chromosome number and structure (CIN). A subgroup with apparently stable, near-diploid chromosomes and stable microsatellites (MACS) also exists. These distinctions are important, partly because of their value in highlighting different pathways of carcinogenesis, and partly because of their direct relevance to prognosis. Study of early-onset cancer has often proved a fruitful resource for the identification of the nature and function of cancer susceptibility genes. In a study of colorectal cancer with stable microsatellite DNA, we describe 22 early-onset tumours (mean age=33), compared with 16 late-onset tumours (mean age=68). Both groups contained carcinomas with the MACS phenotype, characterized by near diploid DNA content, as defined by flow cytometry, and minimal chromosome arm deletion or amplification (six or less events per genome), determined by comparative genomic hybridization (CGH). Minimal chromosome imbalance correlated strongly with diploid DNA content (P<0.001). The proportion of MACS cancers was significantly greater in early-onset as compared to late-onset tumours (64 vs 13%, P=0.005). Of the chromosome arm imbalances commonly observed in late-onset tumours, only 18q- was observed more than twice amongst the 14 early-onset MACS tumours. Seventy-nine per cent of these MACS tumours were located in the distal colon, and 69% were at advanced clinico-pathological stages (with lymph node or distant metastasis). A positive family history of colorectal or other cancers was elicited in seven patients in the MACS early-onset group, and one additional patient in this group had a metachronous ovarian cancer. The results suggest that MACS cancer may have a genetic basis different from either MIN or CIN, and further studies of these cancers may lead to discovery of new mechanisms of colorectal carcinogenesis and cancer susceptibility.

A novel germline 1.8-kb deletion of hMLH1 mimicking alternative splicing: a founder mutation in the Chinese population

We have previously reported that there is a high incidence of microsatellite instability (MSI) and germline mismatch repair gene mutation in colorectal cancer arising from young Hong Kong Chinese. Most of the germline mutations involve hMSH2, which is different from the mutation spectrum in the Western population. It is well known that alternative splicing is common in hMLH1, which complicates RNA based mutation detection methods. In contrast, large deletions in hMLH1, commonly observed in some ethnic groups, tend to escape detection by exon-by-exon direct DNA sequencing. Here we report the detection of a novel germline 1.8 kb deletion involving exon 11 of hMLH1 in a local hereditary non-polyposis colorectal cancer family. This mutation generates a mRNA transcript with deletion of exons 10-11, which is indistinguishable from one of the most common and predominant hMLH1 splice variants. A diagnostic test based on PCR of the breakpoint region led to the identification of an additional young colorectal cancer patient with this mutation. Haplotype analysis suggests that they may share a common ancestral mutation. Our results caution investigators in the interpretation of alternative splicing and have important implications for the design of hMLH1 mutation detection strategy in the Chinese population.