Biomedical subjects
J A Fletcher
Publications and source records attributed to J A Fletcher.
Both DQA1 and DQB1 genes are implicated in HLA-associated protection from type 1 (insulin-dependent) diabetes mellitus in a British Caucasian population.
Inherited susceptibility to Type 1 (insulin-dependent) diabetes mellitus is partly determined by HLA genes. It has been suggested that protection from disease may be conferred by HLA-DQB1 genes which encode molecules with aspartate at position 57. We investigated the contributions of HLA-DRB1, DQA1 and DQB1 genes to protection from disease. Restriction fragment length polymorphism and sequence specific oligonucleotide analysis in 156 British Caucasian Type 1 diabetic and 116 control subjects showed protection from disease was associated with DR2, DRw6 and DR7 haplotypes. The most protective DQA1 allele was DQA1*0102 which occurred on both DR2 and DRw6 haplotypes. The DQB1 alleles DQB1*0303, DQB1*0602 and DQB1*0603 were associated with protection, as was DQB1*0604, which encodes an Asp-57 negative DQ beta molecule. Heterozygosity for both protective and predisposing HLA markers was reduced in diabetic compared with control subjects. We conclude that both DQA1 and DQB1 genes are implicated in HLA-associated protection from Type 1 diabetes in this British Caucasian population. The overall structure of the DQ heterodimer is critical and DQ beta-Asp 57 is of secondary importance in determining protection from disease. The effect of protective HLA types may predominate over that of predisposing markers.
Lineage-restricted chromosome translocation in a benign fibrous tumor of the breast.
We describe a clonal chromosome rearrangement, t(4;14)(q24-25;q24.3), in a benign fibrous tumor of the breast. This is the first reported cytogenetic analysis of a fibrous tumor of the breast and the first evidence for clonality in these lesions. A combined immunohistochemical/cytogenetic study demonstrated that cells with the clonal translocation were mesenchymal. Epithelial cells, in contrast, had normal chromosomes.
Fluorescent in situ hybridization assessment of chromosome 7 copy number in uncultured lung and kidney cells.
Trisomy 7 is common in cells cultured from nonneoplastic lung and kidney tissues, but the frequency of trisomy 7 in uncultured lung and kidney has not been determined. In this study, we used fluorescent in situ hybridization (FISH) to assess chromosome 7 copy number in uncultured interphase nuclei from lung and kidney specimens. All specimens had low level mosaicism for trisomy 7(1.5-5.25%), but control experiments indicated a potential wide margin of error in quantifying these events.
Radiosensitivity in vitro of human soft tissue sarcoma cell lines and skin fibroblasts derived from the same patients.
Skin fibroblast cell strains and tumour cell lines were established from 12 patients with various types of soft tissue neoplasms, and radiation survival curve parameters were measured in vitro. Soft tissue sarcoma cells were consistently more sensitive to X-irradiation than fibroblasts isolated from the same patient, and were also more sensitive as a group than cell lines derived from 34 other human tumours. There was a general correlation in radiosensitivity between fibroblasts and tumour cells derived from the same patient, indicating that some component of tumour cell sensitivity may relate to genetic factors in the host. Such genetic factors, however, do not explain all of the heterogeneity in tumour cell response. The response of soft tissue sarcoma in vivo may be dependent on complex radiomodifying factors other than inherent radiation sensitivity, thus making it difficult to predict clinical outcome by use of assays which use survival of irradiated tumour cell lines in vitro as an endpoint.
Cytogenetics and experimental models of sarcomas.
The sarcomas are an extremely heterogeneous group of neoplasms that continue to present substantial diagnostic and therapeutic challenges. It is notable, therefore, that great strides have been made in the genetic characterization of sarcomas over the past few years. The very consistent chromosome translocations in Ewing's sarcoma, myxoid liposarcoma, and alveolar rhabdomyosarcoma have been cloned, and the oncogenes deregulated by these translocations have been identified. These characteristic genetic aberrations can now be used as diagnostic markers.
Chromosome aberrations in mesoblastic nephroma.
Mesoblastic nephroma (MN) is the most common renal tumor diagnosed in infancy. Histologically, MNs are designated as classic, cellular, or mixed type based upon variations in cellularity. Recent karyotypic reports have suggested that extra copies of chromosome 11 are a nonrandom occurrence in MNs. We analyzed nuclear suspensions prepared from a group of 17 formalin-fixed, paraffin-embedded tumors to determine the possible role of chromosome 11 copy number in the genesis of MN. Extra copies of D11Z1 (a probe for the centromeric region of chromosome 11) were detected in seven out of 10 MNs with cellular or mixed histology, whereas each of six classic histology MNs were disomic for D11Z1 (P < 0.05). Additional fluorescence in situ hybridization studies utilizing the probes for the alpha satellite, centromeric regions of chromosomes 7, 8, 9, 12, 17, and 20 were then carried out on all cases with cellular or mixed histology. Five out of 10 cellular or mixed MNs had extra copies of D8Z1, and four out of 10 had extra copies of D17Z1, suggesting that gains of chromosomes 8 and 17 may be additional nonrandom cytogenetic events associated with the evolution of MNs. DNA aneuploidy, as determined by image analysis, was detected in three tumors: all had greater than four chromosomal aberrations documented by fluorescence in situ hybridization.
Clonal rearrangement of chromosome band 6p21 in the mesenchymal component of pulmonary chondroid hamartoma.
Pulmonary chondroid hamartomas (PCH) are biphasic benign tumors that contain both mesenchymal and epithelial populations. In this report we describe two PCH in which clonal translocations at chromosome band 6p21 were demonstrated in mesenchymal cells. One of these had a unique translocation, t(6;14)(p21;q24), that was also found in one of two PCH karyotyped previously. The t(6;14) has not been described in other varieties of benign or malignant neoplasia. The 6p21 aberrations are of particular interest because break points in this chromosomal region appear to be characteristic of endometrial polyps. Endometrial polyps, like PCH, are biphasic benign tumors in which mesenchymal clonality has been demonstrated.
Cytogenetic evidence for a chromosome 22 tumor suppressor gene in ependymoma.
Although ependymomas comprise 5-10% of pediatric brain tumors, consistent cytogenetic aberrations have not been identified in these neoplasms. We report karyotypes for two ependymomas. A predominantly well-differentiated ependymoma contained several numerical chromosome aberrations, including monosomy 22. In contrast, an anaplastic ependymoma had a more complex karyotype that included loss of one chromosome 22 homologue and a balanced translocation at q13.3 in the remaining 22 homologue. These findings suggest the location of an ependymoma tumor suppressor gene on the long arm of chromosome 22.
Aberrant regulation of ras proteins in malignant tumour cells from type 1 neurofibromatosis patients.
Defects in the NF1 gene have been implicated in the inherited disorder neurofibromatosis type 1, which is characterized by several developmental abnormalities including an increased frequency of benign and malignant tumours of neural crest origin (neurofibromas and neurofibrosarcomas respectively). The NF1 gene encodes a ubiquitous protein homologous to p120GAP, the GTPase-activating protein (GAP) for the products of the ras protooncogenes. When expressed in non-mammalian systems, the region of the NF1 gene homologous to p120GAP produces a protein with GAP-like activity. Here we present evidence that the ras proteins in malignant tumour cell lines from patients with type 1 neurofibromatosis are in a constitutively activated state, as judged by the guanine nucleotide bound to them, and are necessary for cellular proliferation. These cells contain p21ras and p120GAP that are both functionally wild type, but barely any functional NF1 protein. Our results show that the NF1 protein is normally essential for correct negative regulation of ras proteins in the cell, even in the presence of normal p120GAP, and they support the hypothesis that NF1 is a tumour-suppressor gene whose product acts upstream of ras.
Abnormal regulation of mammalian p21ras contributes to malignant tumor growth in von Recklinghausen (type 1) neurofibromatosis.
Tumor cell lines derived from malignant schwannomas removed from patients with neurofibromatosis type 1 (NF1) have been examined for the level of expression of NF1 protein. All three NF1 lines examined expressed lower levels of NF1 protein than control cells, and the level in one line was barely detectable. The tumor lines expressed normal levels of p120GAP and p21ras. Although the p21ras proteins isolated from the tumor cells had normal (nonmutant) biochemical properties in vitro, they displayed elevated levels of bound GTP in vivo. The level of total cellular GAP-like activity was reduced in extracts from the tumor line that expresses very little NF1 protein. Introduction of the catalytic region of GAP into this line resulted in morphological reversion and lower in vivo GTP binding by endogenous p21ras. These data implicate NF1 protein as a tumor suppressor gene product that negatively regulates p21ras and define a "positive" growth role for ras activity in NF1 malignancies.
Trisomy 5 and trisomy 7 are nonrandom aberrations in pigmented villonodular synovitis: confirmation of trisomy 7 in uncultured cells.
Pigmented villonodular synovitis (PVNS) is a proliferative lesion of disputed genesis. Recently, we reported trisomy 7 in short-term cultures of 1 PVNS. In the present report, we describe another specimen of PVNS in which 9 of 26 (35 percent) metaphase cells demonstrated trisomy 7 when analyzed after 3-15 days of tissue culture. In situ hybridization analysis, with a biotinylated probe to chromosome 7 alpha-satellite DNA, revealed trisomy 7 in 53 of 200 uncultured cells from this PVNS sample. Our findings indicate that trisomy 7 is a nonrandom aberration that arises in vivo in PVNS.
Translocation (12;22)(q13-14;q12) is a nonrandom aberration in soft-tissue clear-cell sarcoma.
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Clonal 6p21 rearrangement is restricted to the mesenchymal component of an endometrial polyp.
Previous cytogenetic analyses revealed t(6;20)(p21;q13) in two endometrial polyps. We karyotyped a large endometrial polyp in which 19 of 25 metaphase cells contained a t(1;6;4)(q21;p21;q13). Subsequent combined immunohistochemical/cytogenetic analysis showed all aberrant metaphase cells to be of mesenchymal derivation, whereas epithelial cells from the polyp were diploid. These studies indicate that rearrangement of chromosome band 6p21 is a characteristic cytogenetic aberration in the stromal component of endometrial polyps.
Molecular characterization of a 17q11.2 translocation in a malignant schwannoma cell line.
Malignant schwannomas are soft-tissue neoplasms that occur at increased frequency with germline alterations of the neurofibromatosis-1 (NF1) gene at 17q11.2. We report molecular and cytogenetic characterization of a malignant schwannoma cell line established from an individual affected with NF1. This cell line has a complex hyperdiploid karyotype with two cytogenetically identical der(13)t(13;17)(p11,q11.2) chromosomes. Using somatic cell hybrids, we mapped twelve chromosome-17 probes to either the der(13)t(13;17) chromosome or a small der(17) chromosome. Two chromosome-17p loci, including the p53 tumor suppressor gene, were present in the schwannoma cell line, but did not map to either of these chromosomes. Loss of heterozygosity studies indicated that the two der(13)t(13;17) chromosomes arose by duplication, presumably after the translocation event. The 17q11.2 translocation break-point maps distal to the NF1 gene, and may not disrupt its functioning. Although NF1 mRNA was detected in this cell line by polymerase chain reaction, Northern blot analysis revealed very little or none of the 13-kb mature NF1 transcript. This suggests that the single remaining allele of the NF1 gene contains a mutation that results in either greatly reduced transcription or message instability.
HLA class II gene polymorphism contributes little to Hashimoto's thyroiditis.
UNLABELLED: Previous studies of HLA and Hashimoto's thyroiditis have shown weak associations between the disease and various HLA-DR antigens. OBJECTIVE: To define better the contribution of HLA class II alleles to susceptibility to Hashimoto's thyroiditis. DESIGN AND MEASUREMENTS: Comparison of HLA-DRB, DQA and DQB restriction fragment length polymorphisms in patients with Hashimoto's thyroiditis and control subjects, and meta-analysis of this and other published studies. PATIENTS: Fifty Caucasian patients with Hashimoto's thyroiditis and 93 racially-matched control subjects. RESULTS: A 4.6 kb Taq 1 DQA restriction fragment length polymorphism occurred in 60% of patients compared with 35.5% of controls, Pc < 0.025. No other restriction fragment length polymorphism was significantly associated with the disease. Meta-analysis of several studies demonstrated weak, positive associations between the disease and DR3 and DR4. An association with DR5 was not significant. CONCLUSIONS: DR antigens are unlikely to determine disease susceptibility directly. These findings indicate that any contribution of HLA genes to inherited susceptibility to Hashimoto's thyroiditis is small and requires confirmation in family studies.
Susceptibility to IDDM in a Chinese population. Role of HLA class II alleles.
MHC associations with IDDM in a Chinese population were studied to investigate genetic susceptibility to the disorder. The frequency of HLA-DR3 was significantly higher in the diabetic patients (19/49 [38.7%] vs. control subjects, 11/105 [10.5%], Pc less than 1.3 x 10(-3), RR = 5.3 [CI 2.3-12.1]), whereas DR4 was not (11/49 [22.4%] vs. 28/105 [26.7%], NS). The frequency of DR3/4 heterozygosity was higher in the diabetic patients (6/49 [12.2%] vs. control subjects, 0/105 [0%], P = 1.7 x 10(-3), RR = 31.5 [CI 3.8-263.6]). The frequency of DR3/9 heterozygosity also was higher in the diabetic patients (6/49 [12.2%] vs. control subjects, 2/105 [1.9%], P = 0.03, RR = 6.2 [CI 3.0-12.7]). No significant associations were noted between DQB1 alleles and IDDM. Among DR4-positive subjects, the frequency of DQB1 allele DQB1*0302 was higher in the diabetic patients (10/11 [90.0%] vs. control subjects, 12/24 [50%], Pc less than 0.05, RR = 7.0 [CI 1.3-38.0]), and the frequency of DQB1*0401 was significantly lower in the diabetic patients (2/11 [18.2%] vs. control subjects, 16/24 [66.7%], Pc = 0.04, RR = 0.1 [CI 0.02-0.46]). No DR4 subtype was associated significantly with IDDM. The frequency of DQA1*0501, a DQA1 allele, was higher in diabetic patients (22/41 [53.7%] vs. control subjects, 20/95 [21.1%], Pc less than 3 x 10(-3), RR = 4.3 [CI 2.0-9.3]). The frequency of DQA1*0301, which has been associated consistently with IDDM in other ethnic groups, was not significantly higher in the diabetic patients in this study (27/41 [65.9%] vs. control subjects, 53/95 [55.8%], NS).(ABSTRACT TRUNCATED AT 250 WORDS)
Extremely poor prognosis of pediatric acute lymphoblastic leukemia with translocation (9;22): updated experience.
Approximately five percent of pediatric acute lymphoblastic leukemias (ALL) contain a translocation (9;22)(q34;q11) which results in rearrangement of the bcr and abl genes. At a median follow-up of 5 years, we assessed the prognostic implications of translocation (9;22) in 434 children receiving intensive treatment for ALL. Four-year event-free and overall survivals were only 0% and 20%, respectively, in 15 children with translocation (9;22), but were 81% and 89%, respectively, in 419 children lacking translocation (9;22) (P < 0.001). Based on these findings, we recommend very intensive treatment approaches for all children with translocation (9;22)-positive ALL.