Exome sequencing, ANGPTL3 mutations, and familial combined hypolipidemia.

We sequenced all protein-coding regions of the genome (the "exome") in two family members with combined hypolipidemia, marked by extremely low plasma levels of low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides. These two participants were compound heterozygotes for two distinct nonsense mutations in ANGPTL3 (encoding the angiopoietin-like 3 protein). ANGPTL3 has been reported to inhibit lipoprotein lipase and endothelial lipase, thereby increasing plasma triglyceride and HDL cholesterol levels in rodents. Our finding of ANGPTL3 mutations highlights a role for the gene in LDL cholesterol metabolism in humans and shows the usefulness of exome sequencing for identification of novel genetic causes of inherited disorders. (Funded by the National Human Genome Research Institute and others.).

Prevalence of ANGPTL3 and APOB gene mutations in subjects with combined hypolipidemia.

OBJECTIVE: Mutations of the ANGPTL3 gene have been associated with a novel form of primary hypobetalipoproteinemia, the combined hypolipidemia (cHLP), characterized by low total cholesterol and low HDL-cholesterol levels. The aim of this work is to define the role of ANGPTL3 gene as determinant of the combined hypolipidemia phenotype in 2 large cohorts of 913 among American and Italian subjects with primary hypobetalipoproteinemia (total cholesterol<5th percentile). METHODS AND RESULTS: The combined hypolipidemia cut-offs were chosen according to total cholesterol and HDL-cholesterol levels reported in the ANGPTL3 kindred described to date: total cholesterol levels, <2nd percentile and HDL-cholesterol, levels<2nd decile. Seventy-eight subjects with combined hypolipidemia were analyzed for ANGPTL3 and APOB genes. We identified nonsense and/or missense mutations in ANGPTL3 gene in 8 subjects; no mutations of the APOB gene were found. Mutated ANGPTL3 homozygous/compound heterozygous subjects showed a more severe biochemical phenotype compared to heterozygous or ANGPTL3 negative subjects, although ANGPTL3 heterozygotes did not differ from ANGPTL3 negative subjects. CONCLUSION: These results demonstrated that in a cohort of subjects with severe primary hypobetalipoproteinemia the prevalence of ANGPTL3 gene mutations responsible for a combined hypolipidemia phenotype is about 10%, whereas mutations of APOB gene are absent.

[Effects of gamma irradiation and O2-annealing on optical spectra of Bi doped cadmium tungstate crystal].

The Bi doped tungstate of cadmium crystals were O2-annealed at various temperature, and the absorption and emission spectra of O2-annealed Bi doped tungstate of cadmium crystals were investigated. The absorption intensity decreased, and the absorption side band was shifted to blue short wavelength as the increase of annealing temperature. The emissions at 528 nm and 1 078 nm were observed under excited by 373 and 980 nm, which they were attributed to the intrinsic emission of CdWO4 crystal and emission of Bi5+ ion, respectively. After the crystals were O2-annealed, the 528 nm emission intensity enhanced while the 1 078 nm intensity reduced. It was attributed to the transformation of Bi5+ to Bi3+ ions in the annealing process. After O2-annealed, the transmission of the crystal was enhanced obviously and the color of the crystal became weak. It is attributed to the decrease of oxygen vacancy (Vo) in crystal after the crystal was heated in O2 atmosphere. The 1 078 nm emission intensity reduced while the 528 nm intensity enhanced after the crystals were gamma-irradiated. It may be due to the transormation of Bi5+ to Bi3+ ions through evolution of gamma-irradiated.

Dissociation between intrahepatic triglyceride content and insulin resistance in familial hypobetalipoproteinemia.

BACKGROUND & AIMS: Hepatic steatosis is associated with insulin resistance, but it is not clear whether increased intrahepatic triglyceride (IHTG) content causes the resistance or is a marker. Subjects with familial hypobetalipoproteinemia (FHBL) have high levels of IHTG because of a genetic defect in hepatic export of triglycerides, and provide a unique cohort to study the relationship between steatosis and insulin sensitivity. METHODS: One group of lean subjects with normal IHTG content (2.2% +/- 0.6% of liver volume) (n = 6), and 3 groups of overweight and obese subjects matched for body mass index, were studied: (1) normal IHTG content (3.3% +/- 0.5%; n = 6), (2) high IHTG content (21.4% +/- 2.6%) due to nonalcoholic fatty liver disease (NAFLD; n = 6), and (3) high IHTG content (18.1% +/- 2.2%) due to FHBL (n = 3). A hyperinsulinemic-euglycemic clamp procedure, in conjunction with glucose tracer infusion, was used to determine multiorgan insulin sensitivity. RESULTS: Hepatic insulin sensitivity (reciprocal of glucose rate of appearance [micromol x kg fat-free mass(-1) x min(-1)] x insulin [mU/L]) was greatest in the Lean group (2.0 +/- 0.4); it was the same among subjects with FHBL (0.8 +/- 0.1) and the group with normal IHTG content, matched for body mass index (0.7 +/- 0.1), but greater than the NAFLD group (0.3 +/- 0.1) (P < .01). Muscle insulin sensitivity (percent increase in glucose uptake during insulin infusion) was greatest in the Lean group (576% +/- 70%). Muscle insulin sensitivity was similar in subjects with FHBL and those with normal IHTG (319% +/- 77%, 326% +/- 27%, respectively), but greater than the NAFLD group (145% +/- 18%) (P < .01). CONCLUSIONS: Steatosis is dissociated from insulin resistance in FHBL, which suggests that increased IHTG content is a marker, not a cause, of metabolic dysfunction.

Scaling up syphilis testing in China: implementation beyond the clinic.

China is experiencing a syphilis epidemic of enormous proportions. The regions most heavily affected by syphilis correspond to regions where sexually transmitted HIV infection is also a major public health threat. Many high-risk patients in China fail to receive routine syphilis screening. This missed public health opportunity stems from both a failure of many high-risk individuals to seek clinical care and a disconnect between policy and practice. New point-of-care syphilis testing enables screening in non-traditional settings such as community organizations or sex venues. This paper describes the current Chinese syphilis policies, suggests a spatiotemporal framework (based on targeting high-risk times and places) to improve screening and care practices, and emphasizes a syphilis control policy extending beyond the clinical setting.

Integrated syphilis/HIV screening in China: a qualitative analysis.

BACKGROUND: The last decade has seen enormous advances in HIV treatment and care, but how to implement scaled up HIV testing, prevention, and treatment in low-income areas still presents a formidable public health challenge. South China faces expanding syphilis and sexually transmitted HIV epidemics, but health systems characteristics important for scaling up syphilis and HIV testing have not been defined. METHODS: A purposive sample to ensure public, private, and public-private hybrid STI clinic inclusion was selected in a South China city. Eight key informant interviews were conducted with the STI clinic manager, followed by eight focus group discussions with physicians. Data collection relied on a semi-structured format that included questions in each of the following domains: 1) clinical facilities; 2) laboratory capacity with a focus on syphilis/HIV diagnosis; 3) clinic personnel; 4) physical space with a focus on locations to disclose confidential results; 5) financial support. RESULTS: Public STI clinics had free syphilis testing/treatment and laboratory facilities to perform essential syphilis and HIV tests. However, despite serving a large number of STI patients, private STI clinics lacked nontreponemal syphilis testing, HIV testing, and had fewer connections to the public health infrastructure. Formally trained assistant physicians were 2.5 times as common as physicians at STI clinics. Only one of the 8 sites had onsite voluntary counseling and testing (VCT) services available. CONCLUSION: These STI case studies reveal the potential for expanding integrated syphilis/HIV services at public STI clinics in China. More health services research is needed to guide scale-up of syphilis/HIV testing in China.

Aggressive Prophylactic Treatments for Postoperative Nausea and Vomiting Improve Outcomes in Pediatric Adenotonsillectomy Procedure.

OBJECTIVE: Postoperative nausea and vomiting (PONV) is an extremely common side effect of general anesthesia that is difficult to manage. We tested a hypothesis that an aggressive prophylactic intervention with additional antiemetic drugs will reduce the incidence of PONV in a high-risk pediatric population undergoing adenotonsillectomy. METHODS: In this retrospective study, pediatric patients undergoing adenotonsillectomy were screened for their risk factors for PONV. Patients who had 3 or more risk factors were identified as high risk and received either scopolamine patch preoperatively (for patients over 40 kg body weight) or diphenhydramine immediately postextubation in addition to ondansetron and dexamethasone, which are given routinely. Incidences of PONV within the first 60 minutes of a postanesthesia care unit (PACU) stay were collected and analyzed. RESULTS: Overall postoperative vomiting rates during the first hour of a PACU stay were 4.3% for the group that was treated with dexamethasone and ondansetron only and 3.9% for the group that was treated with additional antiemetic drugs. Aggressive prophylactic management of PONV did reduce the rate of nausea and vomiting in a group of high-risk patients (p < 0.0001). The postoperative antiemetic drug usage was also decreased during the first 60 minutes of a PACU stay. However, the approach did not reduce the overall rate of PONV for the entire study population (p = 0.1612 for nausea and p = 0.0678 for vomiting). CONCLUSION: Aggressive intraoperative management of PONV with additional antiemetic drugs are beneficial in high-risk pediatric population. Intraoperative diphenhydramine usage decreased the rate of PONV. However, preoperative scopolamine patch prevention did not improve PONV, which may be related to the drug's longer onset of action. Our result suggests that current clinical practice is undertreating PONV in pediatric patients receiving general anesthesia.

Fatty liver and insulin resistance: not always linked.

One significant clinical symptom of familial hypobetalipoproteinemia [FHBL] due to defects in apolipoprotein B (apoB) is steatohepatosis. However, the increased hepatic fat content in apoB-related FHBL subjects was not associated with glucose intolerance, in contrast with what is the case in the metabolic syndrome. Meanwhile, in human subjects with similar apoB truncations, degree of obesity and insulin sensitivity, their liver triglyceride (TG) contents may vary considerably, suggesting that, in addition to defective apoB, other genes may affect the magnitude of hepatic TG accumulation. We hypothesized that genetic background affects the severity of hepatic steatosis and the expression of insulin sensitivity. To test the hypotheses, mouse apoB38.9-bearing congenies were bred under high, medium and low liver triglyceride (TG) backgrounds using "speed congenics" approach. These mice were fed on regular diet for 12 weeks. Their insulin sensitivity, serum and liver lipids were assessed. The highest liver fat strain [BALB/cByJ] accumulated significantly higher TG in the liver under apoB38.9 heterozygous condition, while the lowest liver fat strain [SWR/J] had the smallest liver TG change, suggesting that the genetic backgrounds affected the hepatic TG responses to the presence of the apoB38.9 mutation. Interestingly, only the low liver fat strain [SWR/J-apoB38.9] showed significant upward shifts of both glucose tolerance test (GTT) and insulin tolerance test (ITT) curves. Neither the glucose nor the insulin tolerance curves were altered in the two cognate congenics with higher liver fat content [BALB/cByJ and C57BL/6J]. Thus, hepatic TG contents and measures of glucose metabolism were dissociated from each other. It is tempting to conclude that hepatic TG per se may not be responsible for the insulin resistance seen in fatty liver. The genetic/molecular bases for the differences between SWR/J and the other two strains with respect to their glucose metabolic responses to increases in hepatic TG contents remain to be elucidated.

The c.43_44insCTG variation in PCSK9 is associated with low plasma LDL-cholesterol in a Caucasian population.

The genetic etiology of familial hypobetalipoproteinemia (FHBL) is unclear in the majority of cases. Mutations in apolipoprotein B (APOB) are the only confirmed causes of FHBL. Recently, loss-of-function mutations of PCSK9 gene have been shown to be associated with the hypocholesterolemia phenotype. Our primary goal was to confirm that mutations in PCSK9 could be another cause of FHBL. Using the sequencing approach, we found that the c.43_44insCTG variation in PCSK9, a common in-frame insertion in both African American and Caucasian populations, is associated with the hypocholesterolemia phenotype in three FHBL families. Then we tested whether this variation could be associated with lower cholesterol levels in the general population. A total of 403 subjects from a Caucasian population, in which hypobetalipoprotein (HBL) and normal groups were classified using standard criteria, were sequenced for this variation. The allele frequency of this variation in the HBL group was 0.186, but was only 0.128 in the normal lipid group. The mean plasma low-density lipoprotein (LDL)-cholesterol level in subjects heterozygous for this variant is significantly lower than that in the normal group (p<0.01). Heterozygous subjects also had higher high-density lipoprotein (HDL)-cholesterol levels (p<0.01). In general, LDL-cholesterol concentration in individuals with PCSK9 c.43_44insCTG variation was approximately 10-15 mg/dL lower than that in normal individuals. We conclude that the c.43_44insCTG variant plays a role in lowering cholesterol in the general population.

Genetic variants of ApoE account for variability of plasma low-density lipoprotein and apolipoprotein B levels in FHBL.

We report two novel APOB mutations causing short apolipoprotein B (apoB) truncations undetectable in plasma and familial hypobetalipoproteinemia (FHBL). In Family 56, a 5 bp deletion in APOB exon 7 (870_874del5) causes a frame shift, converting tyrosine to a stop codon (Y220X) and producing an apoB-5 truncation. In Family 59, a point mutation (1941G>T) in APOB exon 13 converts glutamic acid to stop codon (E578X), specifying apoB-13. A recurrent mutation in exon 26 (4432delT) produces apoB-30.9 in Family 58. In some members of these families, we observed that plasma low-density lipoprotein (LDL) cholesterol and apoB levels were unusually low even for subjects heterozygous for FHBL. To ascertain whether genetic variations in apolipoprotein E (apoE) would explain some of the variations of apoB and LDL cholesterol levels, apoE genotypes were assessed in affected subjects from a total of eight FHBL families with short apoB truncations. Heterozygous FHBL with the epsilon3/epsilon4 genotype had 10-1 5mg/dL higher plasma LDL cholesterol and apoB levels compared to subjects with the epsilon2/epsilon3 and epsilon3/epsilon3 genotypes. The apoE genotype has been reported to account for approximately 10% of the variation of LDL cholesterol in the general population. It accounted for 15-60% of the variability of plasma LDL cholesterol or apoB levels in our FHBL subjects. The physiologic bases for the greater effects of apoE in FHBL remain to be determined.

Absence of fatty liver in familial hypobetalipoproteinemia linked to chromosome 3p21.

Our aim was to ascertain whether fatty liver may be present in the genetic form of familial hypobetalipoproteinemia (FHBL) linked to a susceptibility locus on chromosome 3p21. Three genetic forms of FHBL exist: (a) FHBL caused by truncation-specifying mutations of apolipoprotein B (apoB), (b) FHBL linked to chr3p21, and (c) FHBL not linked either to APOB or to chr3p21. Fatty liver is common in apoB-defective FHBL. Hepatic fat contents were quantified by magnetic resonance spectroscopy in 16 subjects with 3p21-linked FHBL, 32 subjects with apoB-defective FHBL, and 39 sex- and age-matched controls. Mean liver fat of 3p21 subjects was similar to controls and approximately 60% lower than apoB-defective FHBL subjects ( P = .0012). Indices of adiposity (body mass index, waist/hip ratio) and masses of abdominal subcutaneous, retroperitoneal, and intraperitoneal adipose tissue (IPAT) were quantified by MR imaging. Mean measures of adiposity were similar in the 3 groups, suggesting that adiposity per se was not responsible for differences in liver fat. Liver fat content was positively correlated with IPAT. The intercepts of regression lines of IPAT on liver fat content were similar in controls and 3p21, but higher in apoB-defective FHBL subjects. The slopes of the lines were steepest in apoB-defective, intermediate in 3p21, and flattest in controls. Lipoprotein profiles and very low density lipoprotein-apoB100 kinetics of 3p21 and apoB-defective groups also differed. Thus, 2 genetic subtypes of FHBL also differ in several phenotypic features.

Hepatic fatty acid synthesis is suppressed in mice with fatty livers due to targeted apolipoprotein B38.9 mutation.

Humans and genetically engineered mice with hypobetalipoproteinemia due to truncation-producing mutations of the apolipoprotein B (apoB) gene frequently have fatty livers, because the apoB defect impairs the capacity of livers to export triglycerides (TGs). We assessed the adaptation of hepatic lipid metabolism in our apoB-38.9-bearing mice. Hepatic TG contents were 2- and 4-fold higher in heterozygous and homozygous mice, respectively, compared with wild-type mice. Respective in vivo hepatic fatty acid synthetic rates were reduced to 40% and 15% of the wild-type rate. Hepatic mRNAs for sterol regulatory element-binding protein (SREBP)-1c, fatty acid synthase (FAS), and stearoyl coenzyme A desaturase-1 were coordinately decreased. FAS and SREBP-1c mRNA levels were strongly and positively correlated with each other and inversely correlated with hepatic TGs, suggesting that impaired TG export is a potent inhibitor of fatty acid synthesis. In contrast, levels of plasma beta-hydroxybutyrate and of hepatic carnitine palmitoyl transferase and peroxisome proliferator-activated receptor-alpha mRNAs were not altered, implying that beta-oxidation was not affected. Fasting followed by refeeding increased hepatic fatty acid synthesis 56-fold over fasting in normal and heterozygous mice but only 24-fold in homozygous mice. Parallel changes occurred in FAS and SREBP-1c mRNAs. Thus, impairment of very low density lipoprotein export downregulates hepatic fatty acid synthesis, but the adaptation is incomplete, resulting in fatty livers. The signals mediating suppression of FAS and SREBP-1c levels remain to be identified.

[Temperature-dependence emission properties of Eu(3+)-doped in LiNbO3 single crystal].

The temperature-dependence emission spectra of lower and upper part of Eu(3+) -doped LiNbO3 crystals from 77 to 600 K were investigated under the excitation of a 488 nm light. The results show that, for upper part of crystal, the fluorescence intensity of Eu3+ ions increases with the temperature increase, however, for lower part, the intensity first increases with the temperature increase, and then decreases obviously with temperature increase. The variations of fluorescence intensity for lower and upper part of crystals are explained. The emission intensity of Eu3+ ions in LN is the total effect of thermally excited emission, phonon-assistant absorption and temperature-quenching effect.

Novel mutations of APOB cause ApoB truncations undetectable in plasma and familial hypobetalipoproteinemia.

Familial hypobetalipoproteinemia (FHBL) is a genetic disorder characterized by low levels of apoB-100 and LDL cholesterol. Truncation-producing mutations of apoB (chromosome 2) are among several potential causes of FHBL in patients. Ten new families with FHBL linked to chromosome 2 were identified. In Family 8, a 4432delT in exon 26 produces a frame-shift and a premature stop codon predicted to produce a truncated apoB-30.9. Even though this truncation is just 10 amino acid shorter than the well-documented apoB-31, which is readily detectable in plasma, apoB-30.9 is undetectable. Most truncations shorter than apoB-30 are not detectable in plasma. In Family 34, an acceptor splicing mutation at position -1 of exon 14 changes the acceptor splice site AG to AA. Two families (Family 50 and 52) had mutations (apoB-9 and apoB-29) reported previously. In Family 98, a novel point mutation in exon 26 (11163T>G) causes a premature stop codon, and produces a truncated apoB-80.5 readily detectable in plasma. Sequencing of the ApoB gene in families 1, 5, 18, 58, and 59 did not reveal mutations.

Plasma non-cholesterol sterols in primary hypobetalipoproteinemia.

Primary hypobetalipoproteinemia (pHBL) is characterized by plasma cholesterol levels <5th percentile of a population distribution. Plasma non-cholesterol sterols (NCS) are markers of cholesterol liver synthesis and intestinal absorption. Plasma NCS were measured in 111 pHBL subjects, 108 low cholesterol (LC) and 253 normal cholesterol (NC) controls to gain information on cholesterol metabolism in pHBL, and to assess whether NCS measurements may aid in distinguishing pHBL from LC controls. pHBL subjects compared with LC controls were characterized by increased cholesterol absorption (campesterol/TC) while the synthesis (lathosterol/TC) was not increased. The analysis of pHBL subjects divided by gene defect showed a high campesterol/TC ratio in familial HBL (FHBL) carriers of apolipoproteinB (ApoB) truncations longer than ApoB48 and in FHBL without known gene defect ("not linked"). One not linked kindred was characterized by an increase of the 7-dehydrocholesterol/latho ratio. In a discriminant analysis plasma NCS did not improve the power of TC levels to distinguish FHBL from LC controls. In conclusion, increased cholesterol absorption was found in FHBL subjects harbouring truncations of ApoB>ApoB48, and FHBL harbouring as yet unknown molecular defects. Not linked FHBL kindred are not homogeneous in terms of plasma NCS levels. NCS cannot replace genetic HBL analysis.

A twin response to twin epidemics: integrated HIV/syphilis testing at STI clinics in South China.

BACKGROUND: HIV testing is still stigmatized among many high-risk groups in China, whereas routine syphilis testing has been widely accepted at sexually transmitted infection (STI) clinics. This project used the platform of a rapid syphilis screening test to expand HIV test uptake. The objective of this study was to use multilevel modeling to analyze determinants of syphilis and HIV-testing uptake at STI clinics in China. METHODS: 2061 STI patients at 6 clinics in Guangdong Province were offered free rapid syphilis and free rapid HIV testing. Test uptake was defined by patient receipt of results and a multilevel model was used to analyze predictors of uptake. RESULTS: This was the first syphilis or HIV test for the large majority (1388, 77.7%) of participants. Syphilis test uptake and HIV test uptake were high (1681, 81.6%, syphilis test uptake; 1673, 81.2% HIV test uptake). HIV test uptake was significantly concordant with syphilis test uptake (τb = 0.89, P < 0.001). The most parsimonious model of refusing HIV test uptake included the following variables: being married, having a previous HIV test, being unaccompanied, and participating in the last 2 months of the study. CONCLUSIONS: STI clinic-based screening for syphilis and HIV represents an excellent opportunity for scaling up integrated services, especially in South China where syphilis and sexually transmitted HIV cases are both rapidly increasing. Effective integration of HIV testing into routine clinical practice requires an understanding not only of individual test uptake but also of the broader social context of HIV testing.

Enhanced hepatic apoA-I secretion and peripheral efflux of cholesterol and phospholipid in CD36 null mice.

CD36 facilitates oxidized low density lipoprotein uptake and is implicated in development of atherosclerotic lesions. CD36 also binds unmodified high and very low density lipoproteins (HDL, VLDL) but its role in the metabolism of these particles is unclear. Several polymorphisms in the CD36 gene were recently shown to associate with serum HDL cholesterol. To gain insight into potential mechanisms for these associations we examined HDL metabolism in CD36 null (CD36(-/-)) mice. Feeding CD36(-/-) mice a high cholesterol diet significantly increased serum HDL, cholesterol and phospholipids, as compared to wild type mice. HDL apolipoproteins apoA-I and apoA-IV were increased and shifted to higher density HDL fractions suggesting altered particle maturation. Clearance of dual-labeled HDL was unchanged in CD36(-/-) mice and cholesterol uptake from HDL or LDL by isolated CD36(-/-) hepatocytes was unaltered. However, CD36(-/-) hepatocytes had higher cholesterol and phospholipid efflux rates. In addition, expression and secretion of apoA-I and apoA-IV were increased reflecting enhanced PXR. Similar to hepatocytes, cholesterol and phospholipid efflux were enhanced in CD36(-/-) macrophages without changes in protein levels of ABCA1, ABCG1 or SR-B1. However, biotinylation assays showed increased surface ABCA1 localization in CD36(-/-) cells. In conclusion, CD36 influences reverse cholesterol transport and hepatic ApoA-I production. Both pathways are enhanced in CD36 deficiency, increasing HDL concentrations, which suggests the potential benefit of CD36 inhibition.

Accelerating worldwide syphilis screening through rapid testing: a systematic review.

Syphilis is a persistent public health issue in many low-income countries that have limited capacity for testing, which traditionally relies on a sensitive non-treponemal test and then a specific treponemal test. However, the development of a new rapid treponemal test provides an opportunity to scale up syphilis screening in many settings where traditional tests are unavailable. This systematic review of immunochromatographic strip (ICS) syphilis tests describes the sensitivity and specificity in two important clinical settings: sexually transmitted infection (STI) clinics and antenatal clinics. Clinical data from more than 22 000 whole blood, plasma, or fingerstick ICS tests obtained at STI or antenatal clinics were retrieved from 15 studies. ICS syphilis tests have a high sensitivity (median 0.86, interquartile range 0.75-0.94) and a higher specificity (0.99, 0.98-0.99), both comparable with non-treponemal screening test characteristics. Further research evaluating ICS syphilis tests among primary syphilis cases and among patients infected with HIV will be essential for the effective roll-out of syphilis screening programmes.

Evidence for a quantitative trait locus affecting low levels of apolipoprotein B and low density lipoprotein on chromosome 10 in Caucasian families.

High plasma apolipoprotein B (apoB) and LDL cholesterol levels increase cardiovascular disease risk. These highly correlated measures may be partially controlled by common genetic polymorphisms. To identify chromosomal regions that contain genes causing low plasma levels of one or both parameters in Caucasian families ascertained for familial hypobetalipoproteinemia (FHBL), we conducted a whole-genome scan using 443 microsatellite markers typed in nine multigenerational families with at least two members with FHBL. Both variance components and regression-based linkage methods were used to identify regions of interest. Common linkage regions were identified for both measures on chromosomes 10q25.1-10q26.11 [maximum log of the odds (LOD) = 4.2 for LDL and 3.5 for apoB] and 6q24.3 (maximum LOD = 1.46 for LDL and 1.84 for apoB). There was also evidence for linkage to apoB on chromosome 13q13.2 (LOD = 1.97) and to LDL on chromosome 3p14.1 at 94 centimorgan (LOD = 1.52). Bivariate linkage analysis provided further evidence for loci contributing to both traits (6q24.3, LOD = 1.43; 10q25.1, LOD = 1.74). We evaluated single nucleotide polymorphisms (SNPs) in genes within our linkage regions to identify variants associated with apoB or LDL levels. The most significant finding was for rs2277205 in the 5' untranslated region of acyl-coenzyme A dehydrogenase short/branched chain and LDL (P = 10(-7)). Three additional SNPs were associated with apoB and/or LDL (P < 0.01). Although only the linkage signal on chromosome 10 reached genome-wide statistical significance, there are likely multiple chromosomal regions with variants that contribute to low levels of apoB and LDL and that may protect against coronary heart disease.

A targeted apoB38.9 mutation in mice is associated with reduced hepatic cholesterol synthesis and enhanced lipid peroxidation.

Familial hypobetalipoproteinemia (FHBL) due to truncation-specifying mutations of apolipoprotein B (apoB), which impair hepatic lipid export in very low-density lipoprotein (VLDL) particles, is associated with fatty liver. In an FHBL-like mouse with the apoB38.9 mutation, fatty liver develops despite reduced hepatic fatty acid synthesis. However, hepatic cholesterol contents in apoB38.9 mice are normal. We found that cholesterogenic enzymes (3-hydroxy-3-methylglutaryl-coenzyme A reductase, sterol-C5-desaturase, and 7-dehydrocholesterol reductase) were consistently downregulated in two separate expression-profiling experiments using a total of 19 mice (n = 7 each for apob(+/+) and apob(+/38.9), and n = 5 for apob(38.9/38.9)) and Affymetrix Mu74Av2 GeneChip microarrays. Results were confirmed by real-time PCR. Cholesterol synthesis rates in cultured hepatocytes were reduced by 35% and 25% in apob(38.9/38.9) and apob(+/38.9), respectively, vs. apob(+/+). Hepatic triglycerides and lipid peroxides, the latter measured by thiobarbituric acid-reactive substances (TBARS) assay, were significantly elevated in apob(+/38.9) (117%) and apob(38.9/38.9) (132%) vs. apob(+/+) (100%), as were mRNA expression of the microsomal lipid peroxidizing enzymes Cyp4A10 and Cyp4A14. Hepatic lipid peroxide levels were positively correlated with triglyceride contents (r = 0.601, P = 0.0065). Thus the fatty liver due to a VLDL secretion defect is associated with insufficient adaptation to triglyceride accumulation and with increased lipid peroxidation. In contrast, apoB38.9 mice effectively maintain cholesterol homeostasis in the liver, at least in part, by reducing hepatic cholesterol synthesis.