Vibrio vulnificus septicemia in a patient with the hemochromatosis HFE C282Y mutation.

Vibrio vulnificus is an extremely invasive gram-negative bacillus found in marine waters that causes overwhelming bacteremia and shock that is associated with high mortality. Impaired iron metabolism has been implicated in the susceptibility to V vulnificus bacterial infections. We report a case of fatal V vulnificus sepsis in a 56-year-old man who died within 1 to 3 days after consuming raw seafood. At autopsy, he was found to have micronodular cirrhosis and iron overload. Postmortem genetic analysis revealed the presence of the hemochromatosis gene (HFE) C282Y mutation. To our knowledge, this is this first documented fatal case of V vulnificus infection in a patient proven to carry the HFE C282Y mutation. Because this patient was heterozygous for the major hereditary hemochromatosis mutation and was not previously diagnosed with clinical iron overload, the spectrum of clinical susceptibilities to V vulnificus infection may include carriers of the C282Y mutation.

Cd1d-restricted cellular lysis by peripheral blood lymphocytes: relevance to the inflammatory bowel diseases.

The CD1d molecule has been implicated to play a role in inflammatory bowel diseases (IBD), possibly through its presentation of an intestinal antigen trigger. To understand the role of the CD1d class I-like protein in IBD, we investigated the molecule's expression in diseased intestinal tissue and determined its potential to undergo specific recognition by intraepithelial and peripheral blood lymphocytes (PBLs) derived from IBD patients. We have observed an increase in precipitable CD1d in inflamed tissues, which suggests CD1d up-regulation in IBD; this was not accompanied by the occurrence of CD1d-specific cytotoxicity by lymphocytes isolated from the same tissue sites. In contrast, we have observed CD1d-specific cytotoxicity by PBLs from both patients and normal controls mediated by a possibly unique type of lymphocytic cell. These observations support a model in which intestinal inflammation may be initiated by circulating PBLs following the tissue-specific upregulation of CD1d. These activated PBLs may then be the source of the extraintestinal manifestations observed with IBD. We therefore propose that the cells responsible for this activity may play a role in regulating immune responses through the specific recognition of CD1d-specific antigen(s).

Absence of GNAI2 codon 179 oncogene mutations in inflammatory bowel disease.

The human GNAI2 gene coding for G protein, Galphai2, is located on chromosome 3p21 in proximity to the region where an inflammatory bowel disease (IBD) locus has been suggested. Galphai2-deficient mice develop a lethal diffuse colitis that resembles human ulcerative colitis (UC) and frequently progresses to colon adenocarcinoma. Furthermore, the human GNAI2 gene is subject to point mutations at certain positions, including three at codon 179, all of which have been reported in human endocrine tumors. In order to evaluate the possible involvement of this gene in IBD pathogenesis, we have examined GNAI2 codon 179 sequences in 28 familial IBD patients, including 13 UC, 15 Crohn's disease (CD), and 7 patients with colon cancer/dysplasia, from 12 multiplex IBD families. The wildtype codon 179, CGC for arginine, plus the first G of the codon 180 engender a sequence recognizable by the enzyme BstUI. Mutations, therefore, can result in the abrogation of BstUI digestion of polymerase chain reaction (PCR) products containing the codon 179. Using the PCR-restriction fragment length polymorphism technique, all 28 IBD patients, including those with colon cancer, and 14 non-IBD family members show a BstUI-cleavable PCR-banding pattern indicating the presence of wildtype codon 179. We conclude that, in the familial IBD and colon cancer/dysplasia patients studied, there is no detectable mutation in the codon 179 of the GNAI2 gene.

Gamma delta intraepithelial lymphocytes drive tumor necrosis factor-alpha responsiveness to intestinal iron challenge: relevance to hemochromatosis.

The dependence of intestinal epithelial cell (IEC) growth and differentiation on intraepithelial lymphocytes (IELs) expressing the gamma/delta (gamma delta) T-cell receptor (TCR), suggested a potential role for gamma delta + IELs in the regulation of iron absorption. We therefore examined the levels of hepatic iron and the IEL cytokine responses in C57BL/6J control and class I and TCR knockout lines (placed on a C57BL/6J genetic background) following the administration of supplemental dietary iron. The highest level of liver iron was found in the beta 2-microglobulin knockout (beta 2m-/-) mice followed by the TCR-delta knockout (TCR delta-/-) animals. TCR-alpha knockout (TCR alpha-/-) and control animals did not differ in their iron levels. Liver iron loading correlated inversely with the ability of the mice to generate an IEL tumor necrosis factor (TNF)-alpha response. These observations suggest a model in which IEC iron loading is communicated to IELs via the HFE class I protein. The result of this communication is the initiation of TNF-alpha release by gamma delta + IELs (sustained by macrophages and dendritic cells) contributing to the upregulation of ferritin expression and possibly to the normal maintenance of the IEC apoptotic pathway.

DNA pooling and dense marker maps: a systematic search for genes for cognitive ability.

Pooling DNA from subjects within a group and comparing the pooled DNA across groups for a dense map of DNA markers offers a solution to the conundrum that linkage is systematic but not powerful whereas allelic association is powerful but not systematic. We used DNA pooling to screen 66 markers on chromosome 22 in original and replication samples of children of high general cognitive ability (g) and controls of average g. Although none of these markers survived our three-stage screening design (original pooling, replication pooling, individual genotyping), the results of DNA pooling were largely confirmed by individual genotyping. We can therefore exclude associations of major effect size on chromosome 22 for g, a key variable for cognitive neuroscience research on learning and memory.

DNA pooling identifies QTLs on chromosome 4 for general cognitive ability in children.

General cognitive ability (g), which is related to many aspects of brain functioning, is one of the most heritable traits in neuroscience. Similarly to other heritable quantitatively distributed traits, genetic influence on g is likely to be due to the combined action of many genes of small effect [quantitative trait loci (QTLs)], perhaps several on each chromosome. We used DNA pooling for the first time to search a chromosome systematically with a dense map of DNA markers for allelic associations with g. We screened 147 markers on chromosome 4 such that 85% of the chromosome were estimated to be within 1 cM of a marker. Comparing pooled DNA from 51 children of high g and from 51 controls of average g, 11 significant QTL associations emerged. The association with three of these 11 markers ( D4S2943, MSX1 and D4S1607 ) replicated using DNA pooling in independent samples of 50 children of extremely high g and 50 controls. Furthermore, all three associations were confirmed when each individual was genotyped separately ( D4S2943, P = 0. 00045; MSX1, P = 0.011; D4S1607, P = 0.019). Identifying specific genes responsible for such QTL associations will open new windows in cognitive neuroscience through which to observe pathways between genes and learning and memory.

Dopamine markers and general cognitive ability.

Because general cognitive ability (g) is among the most heritable behavioural traits, it is a reasonable target for a search for quantitative trait loci (QTLs). We used a selected-extremes design to test candidate genes for allelic association with g. Polymorphisms in four genes in the dopamine system (DRD2, DRD3, DRD4, DAT1) were genotyped for 51 high g children with IQ scores > 130 and for 51 average g control children. No significant allelic or genotypic differences were found between the high g and average g groups for these markers of the dopamine system, even though the selected-extremes design provides power to detect QTL associations that involve a relative risk of about 1.5.

Conservation of ancestral haplotypes telomeric of HLA-A.

Genes that predispose to haemochromatosis are though to be located within the several megabases telomeric of HLA-A. Further recombinant mapping has been used previously to map susceptibility genes for diseases such as insulin-dependent diabetes mellitus, myasthenia gravis and cystic fibrosis, and should be useful in relation to haemochromatosis. However, this method requires the recognition of ancestral haplotypes within the susceptibility region. Using a panel of six microsatellite markers from this region (MOG A, MOG B, MOG C, D6S464, D6S306 and D6S105), we show that ancestral haplotypes extend telomeric of HLA-A, at least as far as D6S105. Nine of 14 haplotypes carrying HLA-B7 and HLA-A3 shared the same microsatellite alleles between HLA-A and at least D6S105. Similarly, nine of 10 haplotypes sharing HLA-B8 and HLA-A1 shared the same microsatellite alleles, although a different set to those with HLA-B7 and HLA-A3. Haplotypes representing historical recombination events were also identified. These two findings demonstrate that recombinant mapping may be applicable to the mapping of disease genes in this region.

An increased gamma delta T cell population in the intestine of thymus-leukemia antigen transgenic mice.

In an approach to study thymic leukemia antigen's (TL's) function, we have developed transgenic mice that express T18d on virtually all somatic cells; in such mice, we initially observed changes in T cells within the thymus and lymph nodes as well as the ability of TL to undergo recognition by splenic T cells. As phase II of our study, we now present the results on the composition of gut T cell populations which may be a better measure of TL's true function. We have demonstrated an increase in the number of gamma delta T cells as well as the increase in gamma delta T cells expressing the V gamma 2 chain. These cells appear to be both CD4 and CD8 negative. This suggests that TL may select for a subset of gamma delta T cells within the gut and bolsters earlier reports implicating an H-2T regional gene product as the major histocompatibility complex ligand for gamma delta T cells.

46,XX, inv(6)(p21.1p23) in a pedigree with hereditary haemochromatosis.

Hereditary haemochromatosis (HFE) is a recessive genetic disease of iron overload which has been shown by linkage analysis to reside on the short arm of chromosome 6, close to the major histocompatibility complex (MHC). Positional cloning of the putative HFE locus has been hampered, in part, by the lack of a structural alteration on 6p. In this report, we describe a pedigree with HFE which carries a balanced paracentric inversion of chromosome 6, inv(6)(p21.1p23), a rarely reported chromosomal rearrangement in this region. We have determined the inheritance of the chromosome harbouring the inversion, which segregates as an HFE chromosome. Because the HFE locus has been mapped distal to the HLA-F class I locus at 6p21.3, the breakpoints associated with this chromosomal rearrangement may provide a significant genomic landmark for positional cloning of the HFE gene.

No association between general cognitive ability and the A1 allele of the D2 dopamine receptor gene.

Berman and Noble (1995) reported significantly reduced visuospatial performance in children with the TAQI A1 allele of the D2 dopamine receptor (DRD2) gene. Given that visuospatial performance loads highly on an unrotated principal component indexing general cognitive ability, we tested the association between DRD2 and WISC-R IQ comparing 51 high-IQ, 51 average-IQ, and 35 low-IQ children in the IQ Quantitative Trait Loci (QTL) Project. No statistically significant association between the TAQI A DRD2 alleles and IQ was found. Given that a statistically significant portion of genetic variance for specific cognitive abilities is independent of general cognitive ability, it is possible that the TAQI DRD2 association is specific to visuospatial performance and independent of general cognitive ability.

Transgenic mice expressing the thymus leukemia antigen fail to control cutaneous herpes simplex virus infection.

TL-transgenic mice expressing the thymus leukemia antigen demonstrate a lack of viral clearance following cutaneous HSV infection of the footpad. In this study, both uninfected and HSV-infected TL-transgenic mice demonstrate increased concentrations of IL-4 as well as decreased concentrations of IFN-gamma which may possibly underlie the impairment of viral clearance. Furthermore, lymphocytes from HSV-infected nontransgenic mice, adoptively transferred into HSV-infected TL-transgenic mice, promoted viral clearance and led to an increase in IFN-gamma production. Transgenic mice which were subcutaneously injected with IFN-gamma in the right footpad were also capable of clearing the viral challenge; however, clearance was restricted solely to the right footpad. These studies support the possibility of perturbations in the immune system of TL-transgenic mice and effectively demonstrate the utility of this model system in the study of HSV clearance, persistence, and potential spontaneous reactivation. Moreover, the TL-transgenic animals may provide a useful model system for additional studies requiring a host system skewed toward a Th2 phenotype.

Expansion of natural (NK1+) T cells that express alpha beta T cell receptors in transporters associated with antigen presentation-1 null and thymus leukemia antigen positive mice.

Thymic selection of natural killer-1+ natural T cells that express alpha beta T cell receptors requires a conserved beta 2-microglobulin-associated molecule, presumably CD1d, displayed by CD4+8+ thymocytes. Here we demonstrate that positive selection of natural T cells occurs independent of transporters associated with antigen presentation-1 (TAP-1) function. Moreover, natural T cells in TAP-1o/o mice are numerically expanded. Several H-2 class Ib molecules function in a TAP-independent manner, suggesting that if expressed in TAP-1o/o thymocytes, they could play a role in natural T cell development. Of these class Ib molecules, H-2TL is expressed by TAP-1o/o thymocytes. Moreover, we find that thymi of TL+ mice congenic or transgenic for H-2T18 also have a numerically expanded natural T cell repertoire compared with TL- mice. This expansion, as in TAP-1o/o thymi, is evident in each of the limited T cell receptor V beta chains expressed by natural T cells, suggesting that TL and CD1d impact similar repertoires. Thus TL, in addition to CD1d, plays a role in natural T cell development.

Structure and content of the major histocompatibility complex (MHC) class I regions of the great anthropoid apes.

The origins of the functional class I genes predated human speciation, a phenomenon known as trans-speciation. The retention of class Ia orthologues within the great apes, however, has not been paralleled by studies designed to examine the pseudogene content, organization, and structure of their class I regions. Therefore, we have begun the systematic characterization of the Old World primate MHCs. The numbers and sizes of fragments harboring class I sequences were similar among the chimpanzee, gorilla, and human genomes tested. Both of the gorillas included in our study possessed genomic fragments carrying orthologues of the recently evolved HLA-H pseudogene identical to those found in the human. The overall megabase restriction fragment patterns of humans and chimpanzees appeared slightly more similar to each other, although the HLA-A subregional megabase variants may have been generated following the emergence of Homo sapiens. Based on the results of this initial study, it is difficult to generate a firm species tree and to determine human's closest evolutionary neighbor. Nevertheless, an analysis of MHC subregional similarities and differences in the hominoid apes may ultimately aid in localizing and identifying MHC haplotype-associated disease genes such as idiopathic hemochromatosis.

Thymus-leukemia antigen interacts with T cells and self-peptides.

The functional role of the class Ib thymus-leukemia (TL) Ag expressed within the thymic cortex and intestinal mucosa of the mouse remains unknown. In an approach to elucidate the potential functionality of TL, we developed transgenic mice that ectopically express the H-2T18d gene product on essentially all nucleated cells through the control of a heterologous H-2Kb gene promoter. Transgenic mice demonstrated an increase in the number of CD4+ lymphocytes within the thymus and lymph nodes; these cells displayed an altered T cell receptor repertoire possibly suggesting a role for the ectopically expressed TL protein. The TL protein additionally displayed the characteristics of a bona fide transplantation Ag, because skin grafts from transgenic animals onto MHC- and minor histocompatibility Ag-matched nontransgenic recipient mice resulted in a rapid and vigorous immunologic rejection of the allograft. In MLR studies, transgenic stimulator cells induced the proliferation of responders to a level intermediate between genetically identical and H-2-disparate responder-stimulator combinations. The TL protein was also capable of stimulating cytotoxic T lymphocytes, thereby resulting in specific lysis of TL+ target cells. Further data demonstrated that the TL protein assembles with peptides that are modified at the amino terminus, and that TL retains these molecules at the cell surface. Together, these data suggest that H-2T18d is capable of interacting with T cells via a bound peptide. These data further support the possibility that TL may subserve a specialized function within the immunologic system.

Localization of the hemochromatosis disease gene: linkage disequilibrium analysis using an American patient collection.

The genetic basis of idiopathic hemochromatosis, a common disorder of iron metabolism, has remained an enigma for over two decades. In an attempt to refine the chromosomal localization of this gene, we have conducted a linkage disequilibrium mapping study utilizing a large group of unrelated American patients. The 12 microsatellites used as genetic markers in this analysis include a series of recently described polymorphic dinucleotide (D6S1558, D6S1545 and D6S1554) and tetranucleotide (D6S1016 and D6S1281) repeats which map between D6S105 and D6S299. Haplotype reconstructions indicate that a core genotype, composed of D6S464 allele 3/D6S1260 allele 4/D6S1558 allele 5, exists on a majority of disease chromosomes. Stringent statistical measures of marker-disease disequilibrium suggest that only associations with D6S1260 are significant and furthermore, aid in the assignment of refined centromeric and telomeric limits for the likely location of the hemochromatosis gene. In summary, the genetic data presented in this report predict that the hemochromatosis locus resides between D6S464 and D6S1558, most likely very close to marker D6S1260. Because a single yeast artificial chromosome clone contains all three of the above loci, a thorough search for coding sequences in this region is likely to identify the gene mutated in this common disorder.

Mapping and characterization of non-HLA multigene assemblages in the human MHC class I region.

The major histocompatibility complex (MHC) class I region has been shown to be associated with a variety of immune and nonimmune disorders. In an effort to initiate steps designed to identify the idiopathic hemochromatosis disease gene (HFE), we have cloned and mapped two expressed messages using probes from the HLA-H subregion that lie immediately distal to the HLA-A9 breakpoint. Although the cDNA clones identify distinct multifragment families that are dispersed throughout the MHC, the gene sequences from which the two cDNA clones derive map centromeric to the HLA-B locus and are absent from the genomes of higher nonhuman primates. This suggests that a syntenic coding segment arose within a highly polymorphic region (TNF to HLA-B interval) as the result of an insertion event following the emergence of Homo sapiens. An additional syntenic cluster exists within a peak of linkage disequilibrium with the HFE gene and may define coding sequences that underlie the defect in genetic iron overload. These data generally support the concept that the class I region is potentially gene-rich and further highlight the possibility that these new coding sequences may play a role in the development of a variety of HLA-linked diseases. The observations presented suggest that interlocus exchanges have played a structural role in the genesis of the human class I region.