Linkage disequilibrium between DNA markers at the low-density lipoprotein receptor gene

2019 George Lyman Duff Memorial Lecture: Three Decades of Examining DNA in Patients With Dyslipidemia

Dyslipidemias include both rare single gene disorders and common conditions that have a complex underlying basis. In London, ON, there is fortuitous close physical proximity between the Lipid Genetics Clinic and the London Regional Genomics Centre. For >30 years, we have applied DNA sequencing of clinical samples to help answer scientific questions. More than 2000 patients referred with dyslipidemias have participated in an ongoing translational research program. In 2013, we transitioned to next-generation sequencing; our targeted panel is designed to concurrently assess both monogenic and polygenic contributions to dyslipidemias. Patient DNA is screened for rare variants underlying 25 mendelian dyslipidemias, including familial hypercholesterolemia, hepatic lipase deficiency, abetalipoproteinemia, and familial chylomicronemia syndrome. Furthermore, polygenic scores for LDL (low-density lipoprotein) and HDL (high-density lipoprotein) cholesterol, and triglycerides are calculated for each patient. We thus simultaneously document both rare and common genetic variants, allowing for a broad view of genetic predisposition for both individual patients and cohorts. For instance, among patients referred with severe hypertriglyceridemia, defined as ≥10 mmol/L (≥885 mg/dL), <1% have a mendelian disorder (ie, autosomal recessive familial chylomicronemia syndrome), ≈15% have heterozygous rare variants (a >3-fold increase over normolipidemic individuals), and ≈35% have an extreme polygenic score (a >3-fold increase over normolipidemic individuals). Other dyslipidemias show a different mix of genetic determinants. Genetic results are discussed with patients and can support clinical decision-making. Integrating DNA testing into clinical care allows for a bidirectional flow of information, which facilitates scientific discoveries and clinical translation.

Low density lipoprotein receptor gene Ava II polymorphism and serum lipid levels in the Guangxi Bai Ku Yao and Han populations

BACKGROUND

Several common genetic polymorphisms in the low density lipoprotein receptor (LDL-R) gene have associated with modifications of serum total cholesterol (TC) and low density lipoprotein cholesterol (LDL-C) levels, but the results are not consistent in different populations. Bai Ku Yao is a special subgroup of the Yao minority in China. The present study was undertaken to detect the association of LDL-R gene Ava Ⅱ polymorphism and serum lipid levels in the Guangxi Bai Ku Yao and Han populations.

METHODS

A total of 1024 subjects of Bai Ku Yao and 792 participants of Han Chinese were randomly selected from our previous stratified randomized cluster samples. Genotyping of the LDL-R gene Ava Ⅱ polymorphism was performed by polymerase chain reaction and restriction fragment length polymorphism combined with gel electrophoresis, and then confirmed by direct sequencing.

RESULTS

The levels of serum TC, high density lipoprotein cholesterol (HDL-C), LDL-C, apolipoprotein (Apo) A1 and the ratio of ApoA1 to ApoB were lower in Bai Ku Yao than in Han (P < 0.01 for all). The frequency of A⁻ and A+ alleles was 65.5% and 34.5% in Bai Ku Yao, and 80.7% and 19.3% in Han (P < 0.001); respectively. The frequency of A⁻A⁻, A⁻A+ and A+A+ genotypes was 42.6%, 45.9% and 11.5% in Bai Ku Yao, and 64.9%, 31.6% and 3.5% in Han (P < 0.001); respectively. There was also significant difference in the genotypic frequencies between males and females in Bai Ku Yao (P <0.05), and in the genotypic and allelic frequencies between normal LDL-C (≤ 3.20 mmol/L) and high LDL-C (> 3.20 mmol/L) subgroups in Bai Ku Yao (P < 0.05 for each) and between males and females in Han (P < 0.05 for each). The levels of LDL-C in males and TC and HDL-C in females were different among the three genotypes (P < 0.05 for all) in Bai Ku Yao, whereas the levels of HDL-C in males and HDL-C and ApoA1 in females were different among the three genotypes (P < 0.05-0.001) in Han. The subjects with A+A+ genotype had higher serum LDL-C, TC, HDL-C or ApoA1 levels than the subjects with A-A+ and A⁻A⁻ genotypes. Spearman rank correlation analysis revealed that the levels of LDL-C in Bai Ku Yao and HDL-C in Han were correlated with genotypes (P < 0.05 and P < 0.01; respectively).

CONCLUSIONS

The association of LDL-R gene Ava Ⅱ polymorphism and serum lipid levels is different between the Bai Ku Yao and Han populations. The discrepancy might partly result from different LDL-R gene Ava Ⅱ polymorphism or LDL-R gene-environmental interactions.

A polygenic basis for four classical Fredrickson hyperlipoproteinemia phenotypes that are characterized by hypertriglyceridemia

Numerous single nucleotide polymorphisms (SNPs) have been found in recent genome wide association studies (GWAS) to be associated with subtle plasma triglyceride (TG) variation in normolipidemic subjects. However, since these GWAS did not specifically evaluate patients with rare disorders of lipoprotein metabolism--'hyperlipoproteinemia' (HLP)--it remains largely unresolved whether any of these SNP determinants of modest physiological changes in TG are necessarily also determinants of most HLP phenotypes. To address this question, we evaluated 28 TG-associated SNPs from GWAS in 386 unrelated adult patients with one of five Fredrickson phenotypes (HLP types 2A, 2B, 3, 4 and 5) and 242 matched normolipidemic controls. We found that several SNPs associated with TG in normolipidemic samples, including APOA5 p.S19W and -1131T>C, TRIB1 rs17321515, TBL2 rs17145738, GCKR rs780094, GALNT2 rs4846914 and ANGPTL3 rs12130333, were significantly associated with HLP types 2B, 3, 4 and 5. The findings indicate that: (i) the TG-associated Fredrickson HLP types 2B, 3, 4 and 5 are polygenic traits; (ii) these Fredrickson HLP types share numerous genetic determinants among themselves; and (iii) genetic determinants of modest TG variation in normolipidemic population samples also underlie--to an apparently even greater degree--susceptibility to these rare HLP phenotypes. Thus, the TG-associated Fredrickson HLP types 2B, 3, 4 and 5, although historically considered to be distinct are actually complex traits sharing among them several common genetic determinants seen in GWAS of normolipidemic population samples.

Genetic determinants of statin intolerance

Background

Statin-related skeletal muscle disorders range from benign myalgias – such as non-specific muscle aches or joint pains without elevated serum creatinine kinase (CK) concentration – to true myositis with >10-fold elevation of serum CK, to rhabdomyolysis and myoglobinuria. The genetic basis of statin-related muscle disorders is largely unknown. Because mutations in the COQ2 gene are associated with severe inherited myopathy, we hypothesized that common, mild genetic variation in COQ2 would be associated with inter-individual variation in statin intolerance. We studied 133 subjects who developed myopathy on statin monotherapy and 158 matched controls who tolerated statins without incident or complaint.

Results

COQ2 genotypes, based on two single nucleotide polymorphisms (SNP1 and SNP2) and a 2-SNP haplotype, all showed significant associations with statin intolerance. Specifically, the odds ratios (with 95% confidence intervals) for increased risk of statin intolerance among homozygotes for the rare alleles were 2.42 (0.99 to 5.89), 2.33 (1.13 to 4.81) and 2.58 (1.26 to 5.28) for SNP1 and SNP2 genotypes, and the 2-SNP haplotype, respectively.

Conclusion

These preliminary pharmacogenetic results, if confirmed, are consistent with the idea that statin intolerance which is manifested primarily through muscle symptoms is associated with genomic variation in COQ2 and thus perhaps with the CoQ10 pathway.

A detailed Hapmap of the Sitosterolemia locus spanning 69 kb; differences between Caucasians and African-Americans

Background

Sitosterolemia is an autosomal recessive disorder that maps to the sitosterolemia locus, STSL, on human chromosome 2p21. Two genes, ABCG5 and ABCG8, comprise the STSL and mutations in either cause sitosterolemia. ABCG5 and ABCG8 are thought to have evolved by gene duplication event and are arranged in a head-to-head configuration. We report here a detailed characterization of the STSL in Caucasian and African-American cohorts.

Methods

Caucasian and African-American DNA samples were genotypes for polymorphisms at the STSL locus and haplotype structures determined for this locus

Results

In the Caucasian population, 13 variant single nucleotide polymorphisms (SNPs) were identified and resulting in 24 different haplotypes, compared to 11 SNPs in African-Americans resulting in 40 haplotypes. Three polymorphisms in ABCG8 were unique to the Caucasian population (E238L, INT10-50 and G575R), whereas one variant (A259V) was unique to the African-American population. Allele frequencies of SNPs varied also between these populations.

Conclusion

We confirmed that despite their close proximity to each other, significantly more variations are present in ABCG8 compared to ABCG5. Pairwise D' values showed wide ranges of variation, indicating some of the SNPs were in strong linkage disequilibrium (LD) and some were not. LD was more prevalent in Caucasians than in African-Americans, as would be expected. These data will be useful in analyzing the proposed role of STSL in processes ranging from responsiveness to cholesterol-lowering drugs to selective sterol absorption.

NPC1L1 haplotype is associated with inter-individual variation in plasma low-density lipoprotein response to ezetimibe

BACKGROUND

NPC1L1 encodes a putative intestinal sterol transporter which is the likely target for ezetimibe, a new type of lipid-lowering medication. We previously reported rare non-synonymous mutations in NPC1L1 in an individual who had no plasma lipoprotein response to ezetimibe. We next hypothesized that common variants in NPC1L1 would underlie less extreme inter-individual variations in the plasma LDL cholesterol response to ezetimibe.

RESULTS

In 101 dyslipidemic subjects, we found that NPC1L1 haplotype was significantly associated with inter-individual variation in the response of plasma LDL cholesterol to treatment with ezetimibe for 12 weeks. Specifically, about one subject in eight lacked the common NPC1L1 haplotype 1735C-25342A-27677T and these subjects had a significantly greater reduction in plasma LDL cholesterol with ezetimibe than subjects with at least one copy of this haplotype (-35.9+4.0 versus -23.6+1.6 percent reduction, P = 0.0054). This was paralleled by a similar non-significant trend of between-haplotype difference in reduction of total cholesterol.

CONCLUSION

These preliminary pharmacogenetic results suggest that NPC1L1 variation is associated with inter-individual variation in response to ezetimibe treatment.

Genetic variation in PPARG encoding peroxisome proliferator-activated receptor gamma associated with carotid atherosclerosis

BACKGROUND AND PURPOSE

Peroxisome proliferator-activated receptor gamma is a crucial molecule in atherogenesis because it is associated with metabolic risk factors such as obesity and diabetes and also plays a key role in subcellular metabolism of arterial wall macrophage foam cells. Genetic variation in PPARG has been associated with metabolic and cardiovascular end points.

METHODS

We investigated the relationship between 2 common PPARG polymorphisms, namely P12A and c.1431C>T, and carotid atherosclerosis in a sample of 161 Canadian aboriginal people. Dependent variables were carotid intima media thickness (IMT), assessed using B-mode ultrasonography, and total carotid plaque volume (TPV), assessed using 3D ultrasound.

RESULTS

Using multivariate analysis, we found that subjects with > or =1 PPARG A12 allele had less carotid IMT than others (0.72+/-0.03 versus 0.80+/-0.02 mm; P=0.0045), with no between-genotype difference in TPV. In contrast, subjects with the PPARG c.1431T allele had greater TPV than others (124+/-18.4 versus 65.1+/-23.7 mm3; P=0.0079), with no between-genotype difference in IMT.

CONCLUSIONS

The findings show an association between PPARG genotypes and carotid arterial phenotypes, and further reflect the prevailing view that the PPARG A12 allele protects against deleterious phenotypes. Also, whereas IMT and TPV are somewhat correlated with each other, they might also represent distinct traits with discrete determinants representing different stages of atherogenesis.

Genomic organization and evolution of the CX3CR1/CCR8 chemokine receptor locus

The chemokine receptors CCR8 and CX3CR1 are key players in adaptive immunity and are co-receptors for human immunodeficiency virus. We describe here the genomic organization and evolutionary history of both of these genes. CX3CR1 has three promoters that transcribe three separate exons that are spliced with a fourth exon containing the coding region. CCR8 has two promoters. One promoter produces a transcript of two spliced exons, and the other promoter transcribes an exon containing the coding region and lacks introns. We analyzed these promoters in the context of a luciferase reporter and identified several positive and negative regulatory elements. Identification of the genomic organization of these genes in mouse demonstrates a similar organization for CCR8, but mouse CX3CR1 lacks two of the human promoters and has an additional mouse-specific promoter that transcribes only the exon containing the coding region and therefore resembles the organization of the human and mouse CCR8 genes. We also identify two nontranscribed regions that are highly conserved between human and mouse CX3CR1 containing possible regulatory elements. Examination of the CX3CR1 and CCR8 genes and surrounding genomic regions indicates that these genes are the result of the duplication of an ancestral gene prior to the divergence of teleost fish. We characterize single nucleotide polymorphisms in the promoters of human CCR8 and CX3CR1 and establish linkage relationships between CX3CR1 promoter polymorphisms and two previously described CX3CR1 coding polymorphisms associated with human immunodeficiency virus disease progression and arteriosclerosis susceptibility.

Fine mapping of low-density lipoprotein receptor gene by genetic linkage on chromosome 19p13.1-p13.3 and study of the founder effect of four French Canadian low-density lipoprotein receptor gene mutations

Familial hypercholesterolemia (FH) is one of the most common autosomal codominant diseases. FH is caused by mutations in the low-density lipoprotein receptor (LDLR) gene and is characterized by raised plasma LDL-cholesterol, tendon xanthomas, and premature coronary heart disease. The frequency of FH among French Canadians in northeastern Quebec is higher than in most other populations, 1:154 vs. 1:500 due to high prevalence of few recurrent mutations in the LDLR gene. In the French Canadian population, 11 mutations in the LDLR gene have been found to occur in geographically diverse areas and account for > 90% of cases. We have first constructed a high-resolution genetic map to locate several highly polymorphic markers close to LDLR locus, thus providing the necessary tools to study the origin of the four most common mutations which account for approximately 80% of our FH patients. We have then genotyped five markers (D19S413, D19S865, D19S221, D19S914, D19S586) in 102 heterozygotes (38 del > 15kb; 36 W66G; 16 C646Y; 12 E207K), two compound heterozygotes (del > 15kb/W66G; del > 15kb/C646Y) and seven homozygotes (three del > 15 kb; three W66G: one E207K) with FH unrelated to the first and second degree. We have found that patients bearing the same LDLR gene mutation carry a common haplotype at the LDLR locus although there is evidence for the early occurrence of a recombinational event between the LDLR and the D19S221 locus in the French Canadian patients bearing the W66G mutation. The fine mapping of LDLR gene close to several highly informative microsatellite markers provide fine mapping details of the LDLR region and additional tools for studies of association between plasma lipoprotein levels and LDLR gene.

Genetic variation in factor VII associated with variation in plasma lipoprotein(a) concentration

Cross-sectional and prospective studies have shown that individuals with high plasma lipoprotein(a) [Lp(a)] concentrations are at increased risk for coronary heart disease. Size polymorphism of the apolipoprotein(a) [apo(a)] glycoprotein accounts for approximately 35% of the variation in plasma Lp(a) concentrations. However, there is no convincing evidence for associations between plasma Lp(a) and common genetic variation outside APO(a), the gene that encodes apo(a). We tested for association of common genetic variation of candidate genes in lipid metabolism and also of F7 with variation of plasma Lp(a) concentrations in Alberta Hutterites. Variation at codon 353 of F7 has been associated with variation in the plasma factor VII activity (FVIIc), with the 353Q allele associated with lower FVIIc and the 353R allele associated with higher FVIIc. We found significant associations between variation in plasma concentrations of Lp(a) and both apo(a) isoform size and F7 codon 353 genotype (both P < .0001). The effects on plasma Lp(a) concentration of the alleles at codon 353 were additive. The average effects of the F7 353Q and 353R alleles were, respectively, to decrease by 1.71 micrograms/mL and to increase by 0.301 microgram/mL plasma Lp(a) concentration from the sample mean. This suggests that common genomic variation in F7 is associated with variation in plasma Lp(a) concentration.

Haplotype analysis of hemochromatosis: evaluation of different linkage-disequilibrium approaches and evolution of disease chromosomes

We applied several types of linkage-disequilibrium calculations to analyze the hereditary hemochromatosis (hh) locus. Twenty-four polymorphic markers in the major histocompatibility complex (MHC) class I region were used to haplotype hh and normal chromosomes. A total of 169 hh and 161 normal chromosomes were analyzed. Disequilibrium values were found to be high over an unusually large region beginning 150 kb centromeric of HLA-A and extending nearly 5 Mb telomeric of it. Recombination in this region was approximately 28% of the expected value. This low level of recombination contributes to the unusually broad region of linkage disequilibrium found with hh. The strongest disequilibrium was found at locus HLA-H (delta = .84) and at locus D6S2239 (delta = .85), a marker approximately 10 kb telomeric to HLA-H. All disequilibrium methods employed in this study found peak disequilibrium at HLA-H or D6S2239. The cys282tyr mutation in HLA-H, a candidate gene for hh, was found in 85% of disease chromosomes. A haplotype phylogeny for hh chromosomes was constructed and suggests that the mutation associated with the most common haplotype occurred relatively recently. The age of the hh mutation was estimated to be approximately 60-70 generations. Disequilibrium was maintained over a greater distance for hh-carrying chromosomes, consistent with a recent mutation for hh. Our data provide a reasonable explanation for previous difficulties in localizing the hh locus and provide an evolutionary history for disease chromosomes.

Recombinations defining centromeric and telomeric borders for the hereditary haemochromatosis locus

Hereditary haemochromatosis (HFE) is a common inherited disorder, affecting approximately five per thousand white people of northern European descent. Genetic linkage and linkage disequilibrium studies indicate that the disease locus is tightly linked to HLA-A and D6S105. Recombination between HFE and HLA class I loci is known to be rare. We report here two pedigrees in which recombinations telomeric of HLA-A occurred. These recombinant events define new centromeric and telomeric borders for the HFE locus.

Cladistic analysis of the apolipoprotein AI-CIII-AIV gene cluster using a healthy French Canadian sample. I. Haploid analysis

A cladistic analysis was carried out to identify haplotypes hypothesized to differ for functional DNA sequence variations within the apolipoprotein (apo) AI-CIII-AIV gene cluster that affect plasma lipid, lipoprotein and apolipoprotein levels. A sample of unrelated healthy French Canadians was studied. First, a cladogram of the observed apo AI-CIII-AIV haplotypes was estimated. Then this cladogram was used to define a statistical analysis of the association between haplotype variation and variation in plasma lipid, lipoprotein and apolipoprotein levels. Three haplotypes were identified which were associated with small (5-12% of the total sum of squares) pleiotropic effects on plasma lipid, lipoprotein and apolipoprotein traits and these effects were context, i.e. gender, dependent.

Role of common genetic polymorphisms in the LDL receptor gene in affecting plasma cholesterol levels in the general population

A large number of rare mutations in the low-density lipoprotein (LDL) receptor gene cause the autosomal dominant disorder familial hypercholesterolemia. In addition, a number of common DNA polymorphisms have been identified in the LDL receptor gene, but their significance in affecting plasma cholesterol levels in the general population has not been studied widely. We investigated the role of two common DNA polymorphisms, Ava II (exon 13) and Nco I (exon 18), at the LDL receptor locus in affecting plasma lipid profiles in normolipidemic Hispanics (n = 385) and non-Hispanic whites (NHWs; n = 543) from the San Luis Valley, Colorado. While the distribution of the Nco I polymorphism was comparable between Hispanics and NHWs, the allele frequencies at the Ava II restriction site differed significantly between the two ethnic groups (P < .001). The Ava II and Nco I polymorphisms were in linkage disequilibrium (P < .05) in both Hispanics and NHWs. Both polymorphisms revealed a gender-specific effect on total and LDL cholesterol (LDL-C) confined to women only in both ethnic groups. The AVA II polymorphism was associated significantly with total cholesterol and LDL-C in NHW women (P = .001 and P = .014) and in Hispanic women (P = .011 and P = .057). The effect of the Nco I polymorphism was significant on total cholesterol and LDL-C (P = .019 and P = .035) in Hispanic women only. Although a similar trend was observed in NHW women, the effect was not significant at the 5% level.(ABSTRACT TRUNCATED AT 250 WORDS)

RFLPs of the LDL-receptor gene: their use in the diagnosis of FH and in evaluation of different levels of gene expression on normal subjects

The usefulness of the RFLPs of the LDL-receptor gene in early diagnosis of Familial Hypercholesterolemia (FH) was investigated in 122 FH-families. Four RFLPs, produced by digestion with the enzymes PvuII, ApaLI and AvaII/XbaI were able to detect the affected gene and to follow the inheritance of the disease in 72 out of 97 families (74%). In the remaining 25 families, unambiguous diagnosis was possible in 66% of the cases by use of PvuII, ApaLI and BstEII/EcoRI RFLPs. The RFLPs were also useful to distinguish true homozygotes from compound heterozygotes and to detect families where recombination events occurred or where hypercholesterolemia was not due to a defect of the LDL-receptor gene. In a normal population PvuII RFLP account for 9.6% of the total variance of the LDL cholesterol levels adjusted for confounding variables. The P2 allele was associated with lower LDL cholesterol concentrations (average excess -9.1 mg/dl). This finding allows us to presume there is a DNA sequence, close to the variable PvuII cutting site in intron 15, which could act as an enhancer of the LDL-receptor gene expression.

Haplotype analysis at the low density lipoprotein receptor locus: application to the study of familial hypercholesterolemia in Israel

Familial hypercholesterolemia (FH) results from mutations in the low density lipoprotein (LDL) receptor gene. It has been shown that restriction fragment length polymorphisms (RFLPs) associated with this gene may be used for family and population studies. The present investigation is a population-based study of 19 Jewish families with hypercholesterolemia representing 9 different countries of origin. Ten RFLP sites were used to construct 24 different haplotypes from 112 chromosomes. These haplotypes vary in frequency from 0.9% to 28.6%. Five previously undescribed haplotypes, which comprise 8.1% of the sample, are reported here. The six most common haplotypes account for 70% of the sample. Segregation analysis reveals that, in Israel, distinct LDL receptor haplotypes are associated with hypercholesterolemia in 12 (63%) out of the 19 Jewish families. Five LDL receptor haplotypes co-segregate with hypercholesterolemia. Two of these haplotypes seem to be unique to specific population groups in Israel and may therefore represent founder mutations.

Case report: heterogeneity of aldolase B in hereditary fructose intolerance

Hereditary fructose intolerance (HFI) is a recessive genetic disorder with an estimated disease frequency of 1 in 20,000 and a carrier frequency of 1 in 70. Affected individuals are unable to assimilate fructose from fruit sugars and may develop severe hypoglycemia, metabolic problems, and death if misdiagnosed. Those who survive childhood learn to avoid sweets, effectively preventing further symptoms and complications. The disease is caused by a genetically defective hepatic enzyme, aldolase B. Traditionally, diagnosis has been made by intravenous fructose challenge or by liver biopsy, both difficult and risky invasive tests. Identification of mutations of the aldolase B gene by analysis of DNA from blood leukocytes is now possible, allowing for potential noninvasive diagnosis of subjects at risk in the future. The authors demonstrate heterozygosity for an aldolase B gene mutation in a patient with HFI.

Type III dyslipoproteinemia in patients heterozygous for familial hypercholesterolemia and apolipoprotein E2. Evidence for a gene-gene interaction

In four large pedigrees with heterozygous familial hypercholesterolemia (FH) genetically linked to the low density lipoprotein receptor locus, we have observed a strong interaction between the presence of FH and a single apolipoprotein (apo) E2 allele, resulting in a markedly increased prevalence of type III dyslipoproteinemia (DLPIII). DLPIII was defined by chemical criteria. None of the patients with DLPIII had tuberous or palmar xanthomas characteristic of classically defined type III hyperlipoproteinemia. After exclusion of four persons with apo E 2-2 phenotype, there were 89 FH patients and 110 non-FH subjects. Definite DLPIII (defined as a very low density lipoprotein [VLDL] cholesterol to plasma triglyceride ratio greater than 0.30 with plasma triglycerides greater than or equal to 150 mg/dl) was present in 26% of 43 FH patients with a single E2 allele compared with only 3.4% of 29 non-FH subjects with an E2 allele (p = 0.003). To further characterize this interaction we performed a two-way analysis of covariance, after adjustment for age, sex, and body mass index, to test for any interaction between FH and the apo E loci. There was a statistically significant interaction between FH and the presence of a single E2 allele for the ratio of VLDL cholesterol to plasma triglycerides and for a newly derived estimate of beta-VLDL cholesterol concentration. Estimated beta-VLDL cholesterol level was strongly correlated with age in the subgroup with FH and an E2 allele but not in other subgroups. There was no difference in estimated beta-VLDL cholesterol between sexes. Correlation between estimated beta-VLDL cholesterol level and body mass index in persons older than 18 years was of only marginal significance and of similar magnitude in persons with or without an apo E2 allele. Present knowledge suggests that beta-VLDLs are highly atherogenic; if so, then a sizable subset of FH patients having at least one apo E2 allele and DLPIII may be at increased risk for premature coronary heart disease.

DNA haplotype analysis suggests linkage disequilibrium in the human insulin receptor gene

Haplotypes of the insulin receptor gene were resolved in parents from Scandinavian nuclear families by studying the segregation of seven restriction fragment length polymorphisms (RFLPs). Of 97 unrelated parents, 41 had non-insulin-dependent diabetes mellitus (NIDDM). Considerable linkage disequilibrium in the region of the insulin receptor gene was found. Pairwise non-random associations were found between proximate RFLP sites, indicating the absence of recombinational hot spots between these sites. Thus, association studies between DNA polymorphisms at this locus and disease susceptibility genes could well be feasible in this population. Differences in the distribution of insulin receptor haplotypes were examined between NIDDM patients and healthy subjects. However, the differences observed were not statistically significant.