Hypervariable polymorphism in the APOC3 gene

Citric Acid Cycle Intermediates in Cardioprotection

Over the last decade, there has been a concerted clinical effort to deliver on the laboratory promise that a variety of maneuvers can profoundly increase cardiac tolerance to ischemia and/or reduce additional damage consequent upon reperfusion. Here we will review the proximity of the metabolic approach to clinical practice. Specifically, we will focus on how the citric acid cycle is involved in cardioprotection. Inspired by cross-fertilization between fundamental cancer biology and cardiovascular medicine, a set of metabolic observations have identified novel metabolic pathways, easily manipulable in man, which can harness metabolism to robustly combat ischemia-reperfusion injury.

A common breakpoint on 11q23 in carriers of the constitutional t(11;22) translocation

Structural chromosomal rearrangements occur commonly in the general population. Individuals that carry a balanced translocation are at risk of having unbalanced offspring; therefore, the frequency of translocations in couples with recurrent spontaneous abortions is higher than that in the general population. The constitutional t(11;22) translocation is the most common recurrent non-Robertsonian translocation in humans and may serve as a model to determine the mechanism that causes recurrent meiotic translocations. We previously localized the t(11;22) translocation breakpoint to a region on 22q11 within a low-copy repeat, termed "LCR22." To define the breakpoint on 11q23 and to ascertain whether this region shares homology with LCR22 sequences, we performed haplotype analysis on patients with der(22) syndrome. We found that the breakpoint on 11q23 occurred between two genetic markers, D11S1340 and APOC3-tetra, both being present within a single bacterial-artificial-chromosome clone. To determine whether the breakpoint occurred within the same region among a larger set of carriers, we performed FISH mapping studies. The breakpoints were all within the same clone, suggesting that this region may harbor sequences that are prone to breakage. We narrowed the breakpoint interval, in both derivative chromosomes from two unrelated carriers, to a 190-bp, AT-rich repeat, which indicates that this repeat may mediate recombination events on chromosome 11. Interestingly, the LCR22s harbor AT-rich repeats, suggesting that this sequence motif may mediate recombination events in nonhomologous chromosomes during meiosis.

Anderson's disease: exclusion of apolipoprotein and intracellular lipid transport genes

Anderson's disease is a rare, hereditary hypocholesterolemic syndrome characterized by chronic diarrhea, steatorrhea, and failure to thrive associated with the absence of apo B48-containing lipoproteins. To further define the molecular basis of the disease, we studied 8 affected subjects in 7 unrelated families of North African origin after treatment with a low-fat diet. Lipid loading of intestinal biopsies persisted, but the pattern and extent of loading was variable among the patients. Electron microscopy showed lipoprotein-like particles in membrane-bound compartments, the densities (0.65 to 7.5 particles/mu(2)) and the mean diameters (169 to 580 nm) of which were, in general, significantly larger than in a normal fed subject (0.66 particles/mu(2), 209 nm mean diameter). There were also large lipid particles having diameters up to 7043 nm (average diameters from 368 to 2127 nm) that were not surrounded by a membrane. Rarely, lipoprotein-like particles 50 to 150 nm in diameter were observed in the intercellular spaces. Intestinal organ culture showed that apo B and apo AIV were synthesized with apparently normal molecular weights and that small amounts were secreted in lipid-bound forms (density <1.006 g/mL). Normal microsomal triglyceride transfer protein (MTP) and activity were also detected in intestinal biopsies. Segregation analyses of 4 families excluded, as a cause of the disease, significant regions of the genome surrounding the genes for apo AI, AIV, B, CI, CII, CIII, and E, as were the genes encoding 3 proteins involved in intracellular lipid transport, MTP, and fatty acid binding proteins 1 and 2. The results suggest that a factor other than apoproteins and MTP are important for human intestinal chylomicron assembly and secretion.

European multicenter study on LOH of APOC3 at 11q23 in 766 breast cancer patients: relation to clinical variables. Breast Cancer Somatic Genetics Consortium

High frequencies of loss of heterozygosity (LOH) in chromosome 11q22-qter have been observed in various malignancies, including breast cancer. Previous studies on breast carcinomas by Winqvist et al (Cancer Res 55: 2660-2664) have indicated that a survival factor gene is located in band 11q23, and that the highly informative microsatellite polymorphism at the APOC3 locus would be a suitable tool to perform more extensive LOH studies. In this European multicentre study, we have examined the occurrence of APOC3 LOH and evaluated the effect of LOH of this chromosomal subregion on the clinical behaviour of the disease in a cohort of 766 breast cancer patients in more detail. LOH for APOC3 was found in 42% of the studied tumours, but it was not found to be significantly associated with any of the studied clinical variables, including cancer-specific survival time or survival time after recurrent/metastatic disease. According to the present findings, the putative survival factor gene on 11q23 is not located close enough to the APOC3 gene, but apparently at a more proximal location.

Linkage analysis of candidate genes and the small, dense low-density lipoprotein phenotype

There is accumulating evidence for the importance of small, dense low-density lipoprotein (LDL), the defining feature of the atherogenic lipoprotein phenotype, as a risk factor for coronary heart disease. Although both family studies and twin studies have demonstrated genetic influences on this phenotype, the specific gene(s) involved remain to be identified. The purpose of this study was to determine whether there was evidence for genetic linkage between small, dense LDL (LDL subclass phenotype B), as determined by gradient gel electrophoresis, and selected candidate genes known to be involved in lipid metabolism. The linkage analyses were based on a sample of 19 families, including 142 individual family members, using a lod score linkage analysis approach. Nine candidate genes were examined, including loci for manganese superoxide dismutase (Mn SOD2), apolipoproteins CIII, AII, and apo CII, lipoprotein lipase, hepatic lipase, microsomal triglyceride transport protein, the insulin receptor and the LDL receptor. The analyses did not provide significant evidence for genetic linkage between markers for any of these genes and LDL subclass phenotype B, nor did it confirm previous reports of linkage between the LDL receptor gene and LDL subclass phenotype B. Using three closely linked markers for the Mn SOD2 locus excluded close linkage between this candidate gene region and LDL subclass phenotype B. These findings demonstrate the complexity of genetically mapping risk factor phenotypes, and emphasize the necessity of identifying new genetic loci, other than known candidate genes, involved in susceptibility to atherosclerosis.

Evidence for two distinct tumor-suppressor gene loci on the long arm of chromosome 11 in human oral cancer

Loss of heterozygosity (LOH) on human chromosome 11 has been reported in a variety of human cancers. To search for the existence of tumor-suppressor gene(s) associated with oral squamous cell carcinoma (SCC) on chromosome 11, we have performed high-resolution deletion mapping in 31 patients with oral SCC using 22 microsatellite markers for this chromosomal region. LOH was observed in 14 of 25 cases (56.0%) that were informative with at least one locus. Most allelic deletions detected in our study were specific to the long arm of the chromosome. Furthermore, the data presented here show 2 distinct, commonly deleted regions. The first region, with frequent LOH, was restricted between markers DIIS939 and DIIS924 separated by 3 centimorgans (cM) on chromosome 11q23. The second region of common deletion was identified between markers DIIS912 and DIIS910, separated by 7 cM at 11q25. Our results suggest that at least 2 tumor-suppressor genes involved in the development of oral SCC are present on the long arm of chromosome 11.

Genetic mapping studies of 40 loci and 23 cosmids in chromosome 11p13-11q13, and exclusion of mu-calpain as the multiple endocrine neoplasia type 1 gene

Forty loci (16 polymorphic and 24 non-polymorphic) together with 23 cosmids isolated from a chromosome 11-specific library were used to construct a detailed genetic map of 11p13-11q13. The map was constructed by using a panel of 13 somatic cell hybrids that sub-divided this region into 19 intervals, a meiotic mapping panel of 33 multiple endocrine neoplasia type 1 (MEN1) families (134 affected and 269 unaffected members) and a mitotic mapping panel that was used to identify loss of heterozygosity in 38 MEN1-associated tumours. The results defined the most likely order of the 16 loci as being: 11pter-D11S871-(D11S288, D11S149)-11cen-CNTF-PGA-ROM1-D11S480-PYGM- SEA-D11S913-D11S970-D11S97- D11S146-INT2-D11S971-D11S533-11qter. The meiotic mapping studies indicated that the most likely location of the MEN1 gene was in the interval flanked by PYGM and D11S97, and the results of mitotic mapping suggested a possible location of the MEN1 gene telomeric to SEA. Mapping studies of the gene encoding mu-calpain (CAPN1) located CAPN1 to 11q13 and in the vicinity of the MEN1 locus. However, mutational analysis studies did not detect any germ-line CAPN1 DNA sequence abnormalities in 47 unrelated MEN1 patients and the results therefore exclude CAPN1 as the MEN1 gene. The detailed genetic map that has been constructed of the 11p13-11q13 region should facilitate the construction of a physical map and the identification of candidate genes for disease loci mapped to this region.

G-->A substitution at position -75 of the apolipoprotein A-I gene promoter. Evidence against a direct effect on HDL cholesterol levels

The present study sought to resolve the contradictory evidence as to whether the G-->A substitution at position -75 of the apoA-I gene promoter raises HDL cholesterol (HDL-C) levels by examining the effect of this polymorphism in French Canadians, a relatively genetically homogeneous population. Among 308 women, carriers of the A allele displayed 12% and 10% higher mean plasma HDL-C and apoA-I concentrations, respectively, than did noncarriers. Among 345 men, no effect of the A allele was noted. The frequency distribution of HDL-C levels in women carrying the A but not the G allele appeared bimodal, with one peak corresponding to the mean of the noncarriers and a second to higher HDL-C. Thus it appears that only a subset of A alleles confers high HDL-C levels. This hypothesis was supported by data from four kindreds within which some but not all A alleles segregated with hyperalphalipoproteinemia. The data suggest that the A substitution in the apoA-I gene promoter does not directly confer high HDL-C levels but may be in linkage disequilibrium with other sequence polymorphism(s) at this locus in a subset of alleles that raise HDL-C levels.

Evidence for a cholesterol-lowering gene in a French-Canadian kindred with familial hypercholesterolemia

We describe a four-generation kindred with familial hypercholesterolemia (FH) in which two of the eight heterozygotes for a 5-kb deletion (exons 2 and 3) in the low density lipoprotein (LDL) receptor gene were found to have normal LDL-cholesterol levels. In our search for a gene responsible for the cholesterol-lowering effect in this family, we have studied variation in the genes encoding the LDL receptor, apolipoprotein (apo) B, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, apoAI-CIII-AIV, and lipoprotein lipase. The analysis showed that it was unlikely that variation in any of these genes was responsible for the cholesterol-lowering effect. Expression of the LDL receptor, as assessed in vitro with measurements of activity and mRNA levels, was similar in normo and hyperlipidemic subjects carrying the deletion. Analysis of the apo E isoforms revealed that most of the e2 allele carriers in this family, including the two normolipidemic 5-kb deletion carriers, were found to have LDL-cholesterol levels substantially lower than subjects with the other apo E isoforms. Thus, this kindred provides evidence for the existence of a gene or genes, including the apo e2 allele, with profound effects on LDL-cholesterol levels.

Loss of heterozygosity in cervical carcinoma: subchromosomal localization of a putative tumor-suppressor gene to chromosome 11q22-q24

Infection of cervical epithelial cells with so-called "aggressive" subtypes of human papilloma virus (HPV) appears to be an important factor in the etiology of cervical carcinoma. However, mounting evidence suggests that additional genetic changes are required for progression to an invasive carcinoma. Functional studies have shown that human chromosome 11 contains a gene or genes capable of suppressing tumorigenicity in cell lines derived from different histopathological types of cervical carcinoma, suggesting that aberration of this gene(s) may represent at least one of the additional changes required for tumorigenic progression. To identify the likely chromosomal position of this gene(s), we have carried out a systematic genetic analysis of chromosome 11 in the primary tumors of 32 patients with cervical carcinoma. Sixteen highly polymorphic markers, 10 of which were based on simple sequence repeats typed by PCR, were used to compare matched DNA samples from noninvolved tissue and portions of tumor tissue highly enriched for neoplastic cells by the cryostat-sectioning technique. Of the 32 patients examined, 14 (44%) demonstrated clonal genetic alterations resulting in loss of heterozygosity for one or more markers. Seven of the clonal genetic alterations on chromosome 11 were specific to the long arm, and the overlap between these and other allelic deletions suggests that a suppressor gene(s) relevant to cervical carcinoma maps to chromosome 11q22-q24.