Ankylosing spondylitis is associated with the anthrax toxin receptor 2 gene (ANTXR2)

OBJECTIVES

ANTXR2 variants have been associated with ankylosing spondylitis (AS) in two previous genome-wide association studies (GWAS) (p∼9×10(-8)). However, a genome-wide significant association (p<5×10(-8)) was not observed. We conducted a more comprehensive analysis of ANTXR2 in an independent UK sample to confirm and refine this association.

METHODS

A replication study was carried out with 2978 cases and 8365 controls. Then, these were combined with non-overlapping samples from the two previous GWAS in a meta-analysis. Human leukocyte antigen (HLA)-B27 stratification was also performed to test for ANTXR2-HLA-B27 interaction.

RESULTS

Out of nine single nucleotide polymorphisms (SNP) in the study, five SNPs were nominally associated (p<0.05) with AS in the replication dataset. In the meta-analysis, eight SNPs showed evidence of association, the strongest being with rs12504282 (OR=0.88, p=6.7×10(-9)). Seven of these SNPs showed evidence for association in the HLA-B27-positive subgroup, but none was associated with HLA-B27-negative AS. However, no statistically significant interaction was detected between HLA-B27 and ANTXR2 variants.

CONCLUSIONS

ANTXR2 variants are clearly associated with AS. The top SNPs from two previous GWAS (rs4333130 and rs4389526) and this study (rs12504282) are in strong linkage disequilibrium (r(2)≥0.76). All are located near a putative regulatory region. Further studies are required to clarify the role played by these ANTXR2 variants in AS.

Evidence of cis-acting regulatory variation in PTPN22 in patients with rheumatoid arthritis

OBJECTIVES

To assess whether there are cis-regulatory polymorphisms that regulate protein tyrosine phosphatase, non-receptor type 22 (PTPN22) expression in rheumatoid arthritis (RA).

METHODS

RNA was extracted from positively selected CD56+, CD8+, and CD4+ mononuclear cells and the 'residual' cells from 12 RA patients heterozygous for the PTPN22 C1858T single nucleotide polymorphism (SNP) (rs2476601). Relative allelic expression was measured by single base extension (SBE) assay.

RESULTS

There was relative differential allelic expression (DAE ≥ 20%) in eight patients (p < 10(-5)); seven patients demonstrated DAE in more than one cell type; four patients had statistically significant differences between these cell populations (p(corrected) < 0.05).

CONCLUSIONS

We have demonstrated significant differences in expression of PTPN22 alleles in RA patients, indicating the probable existence of cis-acting regulatory elements.

Evidence of genetic association between TNFRSF1A encoding the p55 tumour necrosis factor receptor, and ankylosing spondylitis in UK Caucasians

OBJECTIVES

To replicate the possible genetic association between ankylosing spondylitis (AS) and TNFRSF1A.

METHODS

TNFRSF1A was re-sequenced in 48 individuals with AS to identify novel polymorphisms. Nine single nucleotide polymorphisms (SNPs) in TNFRSF1A and 5 SNPs in the neighbouring gene SCNN1A were genotyped in 1604 UK Caucasian individuals with AS and 1019 matched controls. An extended study was implemented using additional genotype data on 8 of these SNPs from 1400 historical controls from the 1958 British Birth Cohort. A meta-analysis of previously published results was also undertaken.

RESULTS

One novel variant in intron 6 was identified but no new coding variants. No definite associations were seen in the initial study but in the extended study there were weak associations with rs4149576 (p=0.04) and rs4149577 (p=0.007). In the meta-analysis consistent, somewhat stronger associations were seen with rs4149577 (p=0.002) and rs4149578 (p=0.006).

CONCLUSIONS

These studies confirm the weak genetic associations between AS and TNFRSF1A. In view of the previously reported associations of TNFRSF1A with AS, in Caucasians and Chinese, and the biological plausibility of this candidate gene, replication of this finding in well powered studies is clearly indicated.

Elucidating the chromosome 9 association with AS; CARD9 is a candidate gene

Ankylosing spondylitis (AS) is polygenic with contributions from the immunologically relevant genes HLA-B*27, ERAP1 and IL23R. A recent genome-wide association study (GWAS) identified associations (p~0.005) with the non-synonymous single nucleotide polymorphisms (nsSNPs), rs4077515 and rs3812571, in CARD9 and SNAPC4 on chromosome 9q that had previously been linked to AS. We replicated these associations in a study of 730 AS patients compared to 2879 historic disease controls, (rs4077515 p = 0.0004 odds ratio (OR) (95% confidence interval) = 1.2 (1.1-1.4); rs3812571 p = 0.0003 OR = 1.2 (1.1-1.4)). Meta-analysis revealed strong associations of both SNPs with AS, rs4077515 p = 0.000005 OR = 1.2 (1.1-1.3) and rs3812571 p = 0.000006 OR = 1.2 (1.1-1.3). We then typed 1604 AS cases and 1020 controls for 13 tagging SNPs; 6 showed at least nominal association, 5 of which were in CARD9. We imputed genotypes for 13 additional SNPs but none was more strongly associated with AS than the tagging SNPs. Finally, interrogation of an mRNA expression database revealed that the SNPs most strongly associated AS (or in strong linkage disequilibrium) were those most associated with CARD9 expression. CARD9 is a plausible candidate for AS given its central role in the innate immune response.

Analysis of killer immunoglobulin-like receptor genes in ankylosing spondylitis

OBJECTIVES

To assess the possible association of killer immunoglobulin-like receptor (KIR) genes, specifically KIR3DL1, KIR3DS1 and KIR3DL2, with ankylosing spondylitis (AS).

METHODS

14 KIR genes were genotyped in 200 UK patients with AS and 405 healthy controls using multiplex polymerase chain reaction. Sequence-specific oligonucleotide probes were used to subtype 368 cases with AS and 366 controls for 12 KIR3DL2 alleles. Differences in KIR genotypes and KIR3DL2 allele frequencies were assessed using the chi(2) test.

RESULTS

KIR3DL1 and KIR3DS1 gene frequencies were very similar in cases with AS and controls (odds ratio = 1.5, 95% confidence interval 0.8 to 3.0, and odds ratio = 1.02, 95% confidence interval 0.2 to 5.3, respectively). KIR3DL2 allele frequencies were not significantly different between cases with AS and controls.

CONCLUSIONS

Neither the KIR gene content of particular KIR haplotypes nor KIR3DL2 polymorphisms contribute to AS.

Interleukin-1 promoter region polymorphism role in rheumatoid arthritis: a meta-analysis of IL-1B-511A/G variant reveals association with rheumatoid arthritis

OBJECTIVES

IL-1 has a central role mediating inflammation and joint destruction in RA. Single nucleotide polymorphisms (SNPs) and haplotype structure in the promoter region can modulate IL-1 function. This study examined the effects of four common promoter SNPs in the IL-1 region on susceptibility and clinical characteristics of RA in British Caucasian patients and assessed the risk of RA by meta-analysis of published studies.

METHODS

Using PCR-based methods, 756 RA patients and 625 healthy controls (HCs) were genotyped for IL-1A (-889 C/A, rs17561), IL-1B (-511 A/G, rs16944), IL-1B (-1464 C/G, rs1143623) and IL-1B (-3737 G/A, rs4848306) SNPs. Further meta-analysis was performed for IL-1B (-511 A/G) incorporating 3712 RA patients and 2331 HC from six association studies.

RESULTS

The IL-1B (-1464 C/G) G allele was found to be less common in the RA group [P = 0.01; odds ratio (OR) 1.24; 95% CI 1.04, 1.48]. There was no association between IL-1 SNPs and the presence of HLA-DRB1 shared epitope, RF or clinical characteristics. Meta-analysis revealed statistically significant association between IL-1B (-511 A/G) and RA (P = 0.02; pooled OR 1.13; 95% CI 1.02, 1.26).

CONCLUSIONS

There may be a protective effect in RA from the IL-1B (-1464 C/G) G variant. No direct association between the polymorphisms studied and clinical severity characteristics were observed. Further meta-analysis revealed IL-1B (-511 A/G) to be associated with increased susceptibility to RA.

Fine mapping of the MHC Class III region demonstrates association of AIF1 and rheumatoid arthritis

OBJECTIVES

The heritability of RA has been estimated to be approximately 55%, of which the MHC contributes about one-third. HLA-DRB1 alleles are strongly associated with RA, but it is likely that significant non-DRB1 MHC genetic susceptibility factors are involved. Previously, we identified two three-marker haplotypes in a 106-kb region in the MHC class III region immediately centromeric to TNF, which are strongly associated with RA on HLA-DRB1*0404 haplotypes. In the present study, we aimed to refine these associations further using a combination of genotyping and gene expression studies.

METHODS

Thirty-nine nucleotide polymorphisms (SNPs) were genotyped in 95 DRB1*0404 carrying unrelated RA cases, 125 DRB1*0404-carrying healthy controls and 87 parent-case trio RA families in which the affected child carried HLA-DRB1*04. Quantitative RT-PCR was used to assess the expression of the positional candidate MHC class III genes APOM, BAT2, BAT3, BAT4, BAT5, AIF1, C6orf47, CSNK2beta and LY6G5C, and the housekeeper genes, hypoxanthine-guanine phosphoribosyltransferase (HPRT) and beta(2)-microglobulin (B2M) in 31 RA cases and 21 ethnically, age- and sex-matched healthy controls. Synovial membrane specimens from RA, PsA and OA cases were stained by an indirect immunoperoxidase technique using a mouse-anti-human AIF1 monoclonal antibody.

RESULTS

Association was observed between RA and single markers or two marker haplotypes involving AIF1, BAT3 and CSNK. AIF1 was also significantly overexpressed in RA mononuclear cells (1.5- to 1.9-fold difference, P = 0.02 vs HPRT, P = 0.002 vs B2M). AIF1 protein was clearly expressed by synovial macrophages in all the inflammatory synovial samples in contrast to the non-inflammatory OA samples.

CONCLUSIONS

The results of the genotyping and expression studies presented here suggest a role for AIF1 in both the aetiology and pathogenesis of RA.

MHC2TA promoter polymorphism (-168*G/A, rs3087456) is not associated with susceptibility to rheumatoid arthritis in British Caucasian rheumatoid arthritis patients

OBJECTIVE

To investigate the association of a single-nucleotide polymorphism (SNP) in the promoter region of MHC2TA gene (-168*G/A, rs3087456), which has previously been described in a Swedish rheumatoid arthritis (RA) cohort, in British Caucasian RA patients.

METHODS

We genotyped 733 RA patients and 613 healthy controls for MHC2TA -168*G/A SNP by amplification-refractory mutation system (ARMS). Data were analysed using SPSS version 13.0 software and the chi-square test was applied where appropriate.

RESULTS

The MHC2TA -168*G/A SNP was not associated with increased susceptibility to RA in our patients. Stratifying the patients according to the presence or absence of rheumatoid factor (RF) showed the SNP to be more common in RF negative patients, but this did not reach statistical significance.

CONCLUSION

We did not confirm the previously reported association of this MHC2TA polymorphism with RA in our UK population despite its ethnic similarities with the Swedish population in which it was first described.

Effects of PTPN22 C1858T polymorphism on susceptibility and clinical characteristics of British Caucasian rheumatoid arthritis patients

OBJECTIVES

To confirm the association of a functional single-nucleotide polymorphism (SNP), C1858T (rs2476601), in the PTPN22 gene of British Caucasian rheumatoid arthritis (RA) patients and to evaluate its influence on the RA phenotype.

METHODS

A total of 686 RA patients and 566 healthy volunteers, all of British Caucasian origin, were genotyped for C1858T polymorphism by PCR-restriction fragment length polymorphism assay. Data were analysed using SPSS software and the chi 2 test as applicable.

RESULTS

The PTPN22 1858T risk allele was more prevalent in the RA patients (13.9%) compared with the healthy controls (10.3%) (P = 0.008, odds ratio 1.4, 95% confidence interval 1.09-1.79). The association of the T allele was restricted to those with rheumatoid factor (RF)-positive disease (n = 524, 76.4%) (P = 0.004, odds ratio 1.5, 95% confidence interval 1.1-1.9). We found no association between PTPN22 and the presence of the HLA-DRB1 shared epitope or clinical characteristics.

CONCLUSIONS

We confirmed the previously reported association of PTPN22 with RF-positive RA, which was independent from the HLA-DRB1 genotype.

Finnish HLA studies confirm the increased risk conferred by HLA-B27 homozygosity in ankylosing spondylitis

OBJECTIVE

To determine the influence of HLA-B27 homozygosity and HLA-DRB1 alleles in the susceptibility to, and severity of, ankylosing spondylitis in a Finnish population.

METHODS

673 individuals from 261 families with ankylosing spondylitis were genotyped for HLA-DRB1 alleles and HLA-B27 heterozygosity/homozygosity. The frequencies of HLA-B27 homozygotes in probands from these families were compared with the expected number of HLA-B27 homozygotes in controls under Hardy-Weinberg equilibrium (HWE). The effect of HLA-DRB1 alleles was assessed using a logistic regression procedure conditioned on HLA-B27 and case-control analysis.

RESULTS

HLA-B27 was detected in 93% of cases of ankylosing spondylitis. An overrepresentation of HLA-B27 homozygotes was noted in ankylosing spondylitis (11%) compared with the expected number of HLA-B27 homozygotes under HWE (4%) (odds ratio (OR) = 3.3 (95% confidence interval, 1.6 to 6.8), p = 0.002). HLA-B27 homozygosity was marginally associated with reduced BASDAI (HLA-B27 homozygotes, 4.5 (1.6); HLA-B27 heterozygotes, 5.4 (1.8) (mean (SD)), p = 0.05). Acute anterior uveitis (AAU) was present in significantly more HLA-B27 positive cases (50%) than HLA-B27 negative cases (16%) (OR = 5.4 (1.7 to 17), p<0.004). HLA-B27 positive cases had a lower average age of symptom onset (26.7 (8.0) years) compared with HLA-B27 negative cases (35.7 (11.2) years) (p<0.0001).

CONCLUSIONS

HLA-B27 homozygosity is associated with a moderately increased risk of ankylosing spondylitis compared with HLA-B27 heterozygosity. HLA-B27 positive cases had an earlier age of onset of ankylosing spondylitis than HLA-B27 negative cases and were more likely to develop AAU. HLA-DRB1 alleles may influence the age of symptom onset of ankylosing spondylitis.

A novel human leucocyte antigen-DRB1 genotyping method based on multiplex primer extension reactions

We have developed and validated a semi-automated fluorescent method of genotyping human leucocyte antigen (HLA)-DRB1 alleles, HLA-DRB1*01-16, by multiplex primer extension reactions. This method is based on the extension of a primer that anneals immediately adjacent to the single-nucleotide polymorphism with fluorescent dideoxynucleotide triphosphates (minisequencing), followed by analysis on an ABI Prism 3700 capillary electrophoresis instrument. The validity of the method was confirmed by genotyping 261 individuals using both this method and polymerase chain reaction with sequence-specific primer (PCR-SSP) or sequencing and by demonstrating Mendelian inheritance of HLA-DRB1 alleles in families. Our method provides a rapid means of performing high-throughput HLA-DRB1 genotyping using only two PCR reactions followed by four multiplex primer extension reactions and PCR-SSP for some allele groups. In this article, we describe the method and discuss its advantages and limitations.

The 16189 variant of mitochondrial DNA occurs more frequently in C282Y homozygotes with haemochromatosis than those without iron loading

BACKGROUND

Patients with hereditary haemochromatosis (HH) are usually homozygous for the C282Y mutation in the HFE gene. They have variable expression of iron overload and present with a variety of complications, including liver disease, diabetes, arthropathy, fatigue, and cardiomyopathy. The mitochondrial 16189 variant is associated with diabetes, dilated cardiomyopathy, and low body fat at birth, and might contribute to genetic predisposition in further multifactorial disorders. The objective of this study was to determine the frequency of the 16189 variant in a range of patients with haemochromatosis, who had mutations in the HFE gene.

METHODS

Blood DNA was analysed for the presence of the 16189 variant in British, French, and Australian C282Y homozygotes and controls, with known iron status, and in birth cohorts.

RESULTS

The frequency of the mitochondrial 16189 variant was found to be elevated in individuals with haemochromatosis who were homozygous for the C282Y allele, compared with population controls and with C282Y homozygotes who were asymptomatic (42/292 (14.4%); 102/1186 (8.6%) (p = 0.003); and 2/64 (3.1%) (p = 0.023), respectively).

CONCLUSIONS

Iron loading in C282Y homozygotes with HH was exacerbated by the presence of the mitochondrial 16189 variant.

A targeted approach significantly increases the identification rate of patients with undiagnosed haemochromatosis

OBJECTIVE

To determine the optimal means of identifying patients with undiagnosed haemochromatosis.

DESIGN

Case-control study where cases are defined by the presence of specific clinical diagnoses or symptoms.

SETTING

Primary care patients were recruited from three Oxfordshire practices and secondary care patients were recruited from those patients attending specialist clinics in Amiens University Hospital.

SUBJECTS

A total of 569 patients recruited via hospital clinics and 60 primary care patients (recruited from 4022 consultations) presenting with the following haemochromatosis associated conditions, diabetes, arthralgia/chronic fatigue, osteoporosis or arthropathy were studied. The control group, a total of 991 healthy volunteers, were recruited through a Health Appraisal Centre. Patients and controls were included in the study if they or their family members had not previously been diagnosed with hereditary haemochromatosis.

MAIN OUTCOME MEASURES

Serum ferritin concentration, transferrin saturation (Tsat) and presence of HFE mutations, C282Y and H63D. The check-up in controls consisted of a questionnaire, clinical examination, biochemical tests and screening for the presence of the C282Y and H63D mutations.

RESULTS

Patient groups presenting with unstable diabetes or chronic fatigue and arthralgia together with a raised serum ferritin concentration showed an enrichment in the haemochromatosis-associated genotype HH/YY, odds ratio (OR) = 40.1, confidence interval (CI) = 8.0-202.1 and OR = 103, CI = 22.9-469.7, respectively.

CONCLUSION

Patients presenting to hospital clinics with haemochromatosis associated conditions should be screened biochemically for iron overload. Only those with a serum ferritin >300 microg L-1 or Tsat >40% should subsequently go on to be genotyped for HFE mutations. The patients at greatest risk of having undiagnosed haemochromatosis are those presenting with unstable diabetes, or fatigue and/or arthralgia in the absence of any other explanation.

Uncommon mutations and polymorphisms in the hemochromatosis gene

Hereditary hemochromatosis (HH) is a common autosomal recessive disorder of iron metabolism. Iron absorption from the gut is inappropriately high, resulting in increasing iron overload. The hemochromatosis gene (HFE) was identified in 1996 by extensive positional cloning by many groups over a period of about 20 years. Two missense mutations were identified. Homozygosity for one of these, a substitution of a tyrosine for a conserved cysteine (C282Y), has now clearly been shown to be associated with HH in 60-100% of patients. The role of the second mutation, the substitution of an aspartic acid for a histidine (H63D), is not so clear but compound heterozygotes for both these mutations have a significant risk of developing HH. Here we review other putative mutations in the HFE gene and document a number of diallelic polymorphisms in HFE introns.

Geography of HFE C282Y and H63D mutations

Hereditary hemochromatosis (HH) is a common autosomal recessive disorder causing inappropriate dietary iron absorption that affects North Europeans. HH is associated with the C282Y mutation of the HFE gene, and the H63D mutation to a lesser degree. Both mutations are abundant in Europe, with H63D also appearing in North Africa, the Middle East, and Asia. Emigration from Europe over the past 500 years has introduced C282Y and H63D to America, Australia, New Zealand, and South Africa in an essentially predictable fashion. The distinctive characteristics of the population genetics of HH are the confined racial distribution and high frequency in North European peoples. C282Y frequencies in North Europeans are typically between 5% and 10%, with homozygotes accounting for between 1/100 and 1/400 of these populations. The scarcity of the C282Y mutation in other populations accounts for the lack of HH in non-Europeans.

Detection of C282Y and H63D in the HFE gene

The gene for hemochromatosis was identified in 1996 and two mutations were found. Homozygosity for one of these, C282Y, is associated with hemochromatosis in a high percentage of patients. Genetic analysis of patient DNA is, therefore, a very useful tool to aid and confirm diagnosis and to screen asymptomatic relatives of patients to identify those at risk of developing this common, easily treated disease.

A retrospective anonymous pilot study in screening newborns for HFE mutations in Scandinavian populations

We have retrospectively analyzed 837 random anonymized dried blood spot (DBS) samples from neonatal screening programs in Scandinavia for mutations in HFE, the candidate gene for hemochromatosis. We have found C282Y allele frequencies of 2.3% (+2.0%) (-1.3%) in Greenland, 4.5%+/-1.9% in Iceland, 5.1%+/-2.3% in the Faeroe Islands, and 8.2%+/-2.7% in Denmark. The high prevalence of HFE mutations in Denmark suggests that population screening for the C282Y mutation could be highly advantageous in terms of preventive health care. Long-term follow-up evaluation of C282Y homozygotes and H63D/C282Y compound heterozygotes will give an indication of the penetrance of the mutations.

Multicentric origin of hemochromatosis gene (HFE) mutations

Genetic hemochromatosis (GH) is believed to be a disease restricted to those of European ancestry. In northwestern Europe, >80% of GH patients are homozygous for one mutation, the substitution of tyrosine for cysteine at position 282 (C282Y) in the unprocessed protein. In a proportion of GH patients, two mutations are present, C282Y and H63D. The clinical significance of this second mutation is such that it appears to predispose 1%-2% of compound heterozygotes to expression of the disease. The distribution of the two mutations differ, C282Y being limited to those of northwestern European ancestry and H63D being found at allele frequencies>5%, in Europe, in countries bordering the Mediterranean, in the Middle East, and in the Indian subcontinent. The C282Y mutation occurs on a haplotype that extends </=6 Mb, suggesting that this mutation has arisen during the past 2,000 years. The H63D mutation is older and does not occur on such a large extended haplotype, the haplotype in this case extending </=700 kb. Here we report the finding of the H63D and C282Y mutations on new haplotypes. In Sri Lanka we have found H63D on three new haplotypes and have found C282Y on one new haplotype, demonstrating that these mutations have arisen independently on this island. These results suggest that the HFE gene has been the subject of selection pressure. These selection pressures could be due to infectious diseases, environmental conditions, or other genetic disorders such as anemia.

The effect of HFE mutations on serum ferritin and transferrin saturation in the Jersey population

High frequencies of the haemochromatosis-related HFE C282Y mutation have been reported in North European populations, in which a high proportion of patients with the disease are homozygotes. However, the degree of penetrance of this genotype is unknown. We determined the HFE C282Y and H63D genotypes of 411 consenting volunteer blood donors on Jersey, and the serum ferritin and transferrin saturation levels of 204 of these volunteers. The C282Y allele frequency was found to be 8.3% in 822 chromosomes, indicating a homozygote frequency of 1/145. Consistent with this, four C282Y homozygotes were detected in 411 volunteers. As there are only 18 patients presently receiving treatment for haemochromatosis on Jersey, out of a total population of about 85000, there is a large discrepancy between the number of haemochromatosis patients and the number of C282Y homozygotes in this population. In a preliminary study of 204 consenting volunteers we found a correlation between transferrin saturation and HFE H63D/ C282Y genotype (P=0.017) and between serum ferritin and genotype (P = 0.056). We also observed elevated values of transferrin saturation in the two C282Y homozygotes assayed. These results suggest that a large proportion of the many undetected C282Y homozygotes on Jersey and in similar populations could be in the preclinical stages of haemochromatosis, and warrant investigation. However, there may be a wide variation in the expression of the condition, and a more extensive study of the level of disease penetrance encompassing a large number of hitherto undetected C282Y homozygotes is therefore imperative.

Rapid mapping of markers applying vectorette technology to YAC fragmentation allows easy assembly of a high-density STS bacterial clone contig spanning the markers D6S1260-D6S1918

We have generated a detailed physical map of the 6p21.3/p22.1 boundary, using a combination of yeast artificial chromosome (YAC) fragmentation and high-resolution sequence tagged site (STS) content mapping. YACs from the CEPH, St. Louis, and ICRF libraries have been used to construct a 4.5-Mb contig spanning the markers D6S306 to D6S1571. YAC insert sizes were determined by pulsed field gel electrophoresis (PFGE). Chimerism of YACs was determined by fluorescent in situ hybridization (FISH), and their integrity was determined by fingerprinting with Alu-PCR. We have identified 10 new CA repeat loci in this region as well as over 50 novel STSs, several tRNA genes, a new histone H2B gene and the phospholipase D gene. Using these new markers, we have rapidly generated a bacterial clone contig of over 250 kb, spanning the markers D6S1260 to D6S1918 (WI-3111) with STSs spaced on average every 6 kb.

A rapid non-invasive method for the detection of the haemochromatosis C282Y mutation

We describe the rapid single-step detection, by mutagenically separated polymerase chain reaction (MS-PCR), of the HLE C282Y mutation, for which > 90% of haemochromatosis patients in the U.K. are homozygous. In addition to using purified DNA as a template, whole blood and lysed buccal cell extracts from mouthwash samples can be used. Therefore sample collection may be non-invasive and purification steps kept to a minimum.

Global prevalence of putative haemochromatosis mutations

Haemochromatosis is a genetic disease associated with progressive iron overload, and is common among populations of northern European origin. HLA-H is a recently reported candidate gene for this condition. Two mutations have been identified, a substitution of cysteine for tyrosine at amino acid 282 (C282Y, nucleotide 845) and of histidine for aspartate at amino acid 63 (H63D, nucleotide 187). Over 90% of UK haemochromatosis patients are homozygous for the C282Y mutation. We have examined 5956 chromosomes (2978 people) for the presence of HLA-H C282Y and H63D by PCR followed by restriction enzyme analysis. We have found world wide allele frequencies of 1.9% for C282Y and 8.1% for H63D. The highest frequencies were 10% for C282Y in 90 Irish chromosomes and 30.4% for H63D in 56 Basque chromosomes. C282Y was most frequent in northern European populations and absent from 1042 African chromosomes, 484 Asian chromosomes, and 644 Australasian chromosomes. The distribution of the C282Y mutation coincides with that of populations in which haemochromatosis has been reported and is consistent with the theory of a north European origin for the mutation. The H63D polymorphism is more widely distributed and its connection with haemochromatosis remains unclear.

Measurement of liver fat by MRI and its reduction by dexfenfluramine in NIDDM

OBJECTIVE

To validate a variation of a well-established magnetic resonance imaging (MRI) technique to detect liver fat and use it to monitor liver fat changes after treatment with dexfenfluramine in men with non-insulin dependent diabetes mellitus (NIDDM).

DESIGN

(a) Simple correlation study of MRI Liver Fat Index with liver biopsy results; (b) Open Study of 10 men with NIDDM treated with dexfenfluramine for 12 weeks in addition to their 'usual' therapy.

SUBJECTS

(a) 19 patients (3F; 16M) with abnormal liver function tests undergoing liver biopsy; (b) 10 men, Body Mass Index (BMI) < 30, Waist to hip ratio (WHR) > 0.90 with poorly controlled NIDDM despite oral sulphonylurea therapy.

MEASUREMENTS

(a) MRI liver fat; standard liver biopsy; (b) MRI visceral fat, MRI liver fat, euglycaemic clamp, plasma lipids, fasting glucose and c-peptide levels.

RESULTS

In the validation group, there was a strong relationship between the MRI Liver Fat Index and histopathological assessment of the liver biopsies (r = 0.87, < 0.0001). During treatment with dexfenfluramine the mean Liver Fat Index reduced from 10.6 +/- 3.4 to 6.6 +/- 2.8 (P = 0.05). The reduction in Liver Fat Index correlated with the reduction in visceral fat (r = 0.84, P = 0.001) as well as with the improvement in insulin sensitivity (r = 0.62, P = 0.05). Using partial correlation analysis, the relationship between the change in visceral adipose tissue and the improvement in insulin sensitivity was weaker if the Liver Fat Index was kept constant (r = 0.76 decreased to r = 0.56).

CONCLUSIONS

In this group of subjects MRI Liver Fat Index correlated well with liver fat as seen on biopsy. The Liver Fat Index reduced after 12 weeks therapy with dexfenfluramine suggesting a role for hepatic steatosis in the complex interaction between visceral adipose tissue and insulin sensitivity.

Haemochromatosis: a gene at last?

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The frequency of hemochromatosis-associated alleles is increased in British patients with sporadic porphyria cutanea tarda

The cause of the hepatic siderosis and iron overload that is common in porphyria cutanea tarda (PCT) is uncertain. Heterozygosity for genetic hemochromatosis has been supported by some studies of the association between the HLA-A3 antigen and porphyria cutanea tarda but not by others. The hemochromatosis gene is now believed to be located telomeric to HLA-A3 and close to the DNA microsatellite marker D6S1260. We have used this and other microsatellite markers, which together define an ancestral haplotype that is strongly linked to hemochromatosis, to reinvestigate the relationship between these disorders in 41 British patients with sporadic PCT. Fifteen patients carried the hemochromatosis-associated alleles D6S265-1 and D6S105-8. Four of these were homozygous for the ancestral haplotype D6S265-1 : D6S105-8: D6S1260-4. We estimate that approximately 37% of British patients with sporadic PCT carry at least one hemochromatosis gene compared with 10% of the general population.

Carbohydrate metabolism in insulin resistance: glucose uptake and lactate production by adipose and forearm tissues in vivo before and after a mixed meal

1. To examine whether insulin resistance in vivo is manifest equally in both muscle and adipose tissues, we measured arteriovenous glucose and lactate fluxes across forearm (muscle) and abdominal subcutaneous (adipose) tissue in nine obese, glucose-intolerant subjects and 13 non-obese subjects of similar age and sex. 2. Compared with non-obese subjects, the forearm of the obese subjects was resistant to insulin stimulation of glucose uptake after a mixed meal. In contrast, adipose tissue showed little evidence of insulin stimulation of glucose uptake, and adipose tissue in subjects in both normal and obese groups behaved very similarly (assessed per 100 g of tissue). 3. For lactate flux, adipose tissue behaved very similarly (per 100 g of tissue) in obese and non-obese subjects, and was a consistent lactate exporter. 4. We conclude that insulin resistance of glucose uptake observed in the forearm of obese subjects is not evident in adipose tissue. Adipose tissue glucose uptake in obese, insulin-resistant subjects is similar to that in lean control subjects, although it occurs at elevated circulating insulin and glucose concentrations.

New polymorphic microsatellite markers place the haemochromatosis gene telomeric to D6S105

The haemochromatosis gene (HFE) is linked to both HLA-A and D6S105 on the short arm of chromosome 6 but these markers are separated by approximately 2 Mb of DNA. Most chromosomes carrying HFE have a common haplotype which extends from HLA-A to D6S105 and includes HLA-F. To localise the gene more precisely we have examined 10 microsatellite markers extending over a genetic distance of approximately 5 cM from D6S265 (within 100 kb of HLA-A on the centromeric side) to D6S299 (telomeric). The order of markers is D6S265, HLA-F, D6S258, D6S306, CS3, D6S105, D6S464, CS5, D6S461 and D6S299. We confirm that haemochromatosis appears to originate from a founder mutation which has multiplied in the population through successive generations. This mutation is associated with the haplotype D6S306-5, CS3-3, D6S105-8, D6S464-9 and CS5-4 which is found on approximately 70% of HFE chromosomes. We have applied a new and powerful, likelihood analysis for linkage disequilibrium. The maximum value of lambda (proportion of total possible association between a marker and disease) is 0.74 for marker CS5 (allele 4). A multipoint analysis also gives a maximum likelihood near marker CS5. We conclude that the HFE gene is likely to be located telomeric of D6S105 and close to CS5.

Isolation of CA dinucleotide repeats close to D6S105; linkage disequilibrium with haemochromatosis

The gene for hereditary haemochromatosis (HC) is linked to HLA-A and D6S105 on chromosome 6p. Both markers have also been reported to display linkage disequilibrium with the disease. However, their physical localization relative to one another has not been established. We demonstrate by fluorescent in situ hybridisation that D6S105 lies at least 1-2 Mb telomeric of HLA-A. The haemochromatosis critical region extending from proximal of HLA-A to distal of D6S105 is therefore large. To improve the genetic resolution in this region more highly polymorphic markers are required. We have therefore isolated three novel CA dinucleotide repeats close to D6S105. A linkage disequilibrium study, with two of these microsatellites, in HC patients and controls lends support to the conclusion that D6S105 is a close marker to the haemochromatosis gene.

Effect of vitamin D deficiency on sarcoplasmic reticulum function and troponin C concentration of rabbit skeletal muscle

1. Weanling rabbits were made rachitic either by a vitamin D-deficient diet or by parenteral administration of ethane 1-hydroxy-1,1-diphosphonate (EHDP) in amounts sufficient in other species to block the formation of 1,25-dihydroxycholecalciferol [1,25-(OH)2D3]. 2. The uptake of calcium into the isolated sarcoplasmic reticulum from mixed striated quadriceps muscle, and the amount of troponin C (the calcium-binding component of the troponin complex) in relation to other proteins from the same muscle, were measured. 3. In muscle from animals made rachitic by a dietary deficiency of vitamin D, the rate of uptake of calcium by the sarcoplasmic reticulum and the troponin C concentration were both significantly less (P less than 0.02) than in control littermates. In EHDP-treated animals no significant differences from controls were found. 4. These results show that dietary deficiency of vitamin D in such animals can affect muscle physiology. Since no changes are found in animals made rachitic with EHDP, who presumably have a selective deficiency of 1,25-(OH)2D3, it is possible that the effect of vitamin D on muscle is mediated through metabolites other than 1,25-(OH)2D3 such as 25-hydroxycholecalciferol.

Occurrence of ornithine decarboxylase and polyamines in cartilage

The activity of ornithine decarboxylase was investigated in cartilage from chick embryos, rabbits, rats and human foetuses. The enzyme activity in these cartilages was of the same order as the detected in other body tissues. Ornithine decarboxylase activity in chick-embryo cartilage and liver was the same when compared on the basis of total soluble tissue protein. The cartilage enzyme exhibited a pH optimum of 6.5 and a Km for ornithine of 0.16mM. Ornithine decarboxylase activity in chick-embryo pelvic leaflets was maintained at the value in vivo for up to 22h when the isolated tissue was incubated in a modified Waymouth's medium (MB 752/1) at 37 degrees C. After addition of cycloheximide to the incubation medium, ornithine decarboxylase activity declined, with a half-life of 40 min. The concentrations of the polyamines spermidine and spermine in chick-embryo pelvic cartilage and rabbit costal cartilage were of the same order as the concentrations detected in other tissues.