Gender, body mass index and rheumatoid arthritis disease activity: results from the QUEST-RA Study.

OBJECTIVES: To investigate whether body mass index (BMI), as a proxy for body fat, influences rheumatoid arthritis (RA) disease activity in a gender-specific manner. METHODS: Consecutive patients with RA were enrolled from 25 countries into the QUEST-RA program between 2005 and 2008. Clinical and demographic data were collected by treating rheumatologists and by patient self-report. Distributions of Disease Activity Scores (DAS28), BMI, age, and disease duration were assessed for each country and for the entire dataset; mean values between genders were compared using Student's t-tests. An association between BMI and DAS28 was investigated using linear regression, adjusting for age, disease duration and country. RESULTS: A total of 5,161 RA patients (4,082 women and 1,079 men) were included in the analyses. Overall, women were younger, had longer disease duration, and higher DAS28 scores than men, but BMI was similar between genders. The mean DAS28 scores increased with increasing BMI from normal to overweight and obese, among women, whereas the opposite trend was observed among men. Regression results showed BMI (continuous or categorical) to be associated with DAS28. Compared to the normal BMI range, being obese was associated with a larger difference in mean DAS28 (0.23, 95% CI: 0.11, 0.34) than being overweight (0.12, 95% CI: 0.03, 0.21); being underweight was not associated with disease activity. These associations were more pronounced among women, and were not explained by any single component of the DAS28. CONCLUSIONS: BMI appears to be associated with RA disease activity in women, but not in men.

A narrow and highly significant linkage signal for severe bipolar disorder in the chromosome 5q33 region in Latin American pedigrees.

We previously reported linkage of bipolar disorder to 5q33-q34 in families from two closely related population isolates, the Central Valley of Costa Rica (CVCR) and Antioquia, Colombia (CO). Here we present follow up results from fine-scale mapping in large CVCR and CO families segregating severe bipolar disorder, BP-I, and in 343 population trios/duos from CVCR and CO. Employing densely spaced SNPs to fine map the prior linkage peak region increases linkage evidence and clarifies the position of the putative BP-I locus. We performed two-point linkage analysis with 1134 SNPs in an approximately 9 Mb region between markers D5S410 and D5S422. Combining pedigrees from CVCR and CO yields a LOD score of 4.9 at SNP rs10035961. Two other SNPs (rs7721142 and rs1422795) within the same 94 kb region also displayed LOD scores greater than 4. This linkage peak coincides with our prior microsatellite results and suggests a narrowed BP-I susceptibility regions in these families. To investigate if the locus implicated in the familial form of BP-I also contributes to disease risk in the population, we followed up the family results with association analysis in duo and trio samples, obtaining signals within 2 Mb of the peak linkage signal in the pedigrees; rs12523547 and rs267015 (P = 0.00004 and 0.00016, respectively) in the CO sample and rs244960 in the CVCR sample and the combined sample, with P = 0.00032 and 0.00016, respectively. It remains unclear whether these association results reflect the same locus contributing to BP susceptibility within the extended pedigrees.

Mapping a gene for 46,XY gonadal dysgenesis by linkage analysis.

46,XY gonadal dysgenesis was transmitted as an autosomal-dominant trait in a large family with multiple affected members. Expressivity of the trait was highly variable, ranging from pure to partial gonadal dysgenesis associated with normal female genitalia or sexual ambiguity, to mild hypospadias in otherwise normal males. The phenotypic features of this trait appeared to be confined to the genitourinary system. Multipoint parametric analysis using markers D5S664, D5S633, and D5D2102 yielded an LOD score of 4.47, assuming sex-limited, autosomal-dominant inheritance with a penetrance of 0.6. Because mutation in testis-determining genes leads to gonadal dysgenesis in 46,XY individuals, we postulate that the gene mapped by this study normally plays a role in gonadal differentiation.

A genomewide screen in multiplex rheumatoid arthritis families suggests genetic overlap with other autoimmune diseases.

Rheumatoid arthritis (RA) is an autoimmune/inflammatory disorder with a complex genetic component. We report the first major genomewide screen of multiplex families with RA gathered in the United States. The North American Rheumatoid Arthritis Consortium, using well-defined clinical criteria, has collected 257 families containing 301 affected sibling pairs with RA. A genome screen for allele sharing was performed, using 379 microsatellite markers. A nonparametric analysis using SIBPAL confirmed linkage of the HLA locus to RA (P < .00005), with lambdaHLA = 1.79. However, the analysis also revealed a number of non-HLA loci on chromosomes 1 (D1S235), 4 (D4S1647), 12 (D12S373), 16 (D16S403), and 17 (D17S1301), with evidence for linkage at a significance level of P<.005. Analysis of X-linked markers using the MLOD method from ASPEX also suggests linkage to the telomeric marker DXS6807. Stratifying the families into white or seropositive subgroups revealed some additional markers that showed improvement in significance over the full data set. Several of the regions that showed evidence for nominal significance (P < .05) in our data set had previously been implicated in RA (D16S516 and D17S1301) or in other diseases of an autoimmune nature, including systemic lupus erythematosus (D1S235), inflammatory bowel disease (D4S1647, D5S1462, and D16S516), multiple sclerosis (D12S1052), and ankylosing spondylitis (D16S516). Therefore, genes in the HLA complex play a major role in RA susceptibility, but several other regions also contribute significantly to overall genetic risk.

Unexpected HLA haplotype sharing in dizygotic twin pairs discordant for rheumatoid arthritis.

Dizygotic twins are generally believed to be no more genetically similar than sibs born from separate pregnancies. In the present study, a panel of 93 dizygotic twin pairs discordant for rheumatoid arthritis were typed for HLA-A, -B, -Cw, and -DR antigens. HLA haplotype sharing identical by descent between the twins showed a trend towards increased sharing of both HLA haplotypes; this increased sharing was statistically significant when the female/female twin pairs were considered separately. In contrast, the pattern of HLA haplotype sharing in sib pairs (n = 128) was consistent with a 1:2:1 ratio of 2, 1, or 0 haplotypes shared. An analysis of 16 normal dizygotic twin pairs was consistent with these results raising the possibility that dizygotic twins in general are genetically more similar at the HLA complex than sibs born from separate pregnancies.

HLA-DRB1*0401/0404 genotype and rheumatoid arthritis: increased association in men, young age at onset, and disease severity.

OBJECTIVE: To confirm the reported strong association between the HLA-DRB1*0401/0404 genotype and susceptibility to rheumatoid arthritis (RA), and to investigate the influence of sex, age at disease onset, and variables of disease severity on the strength of this association. METHODS: A case control design was adopted comparing the frequency of specific HLA-DRB1 genotypes between 201 Caucasian patients with RA and 139 controls. HLA typing was performed using a polymerase chain reaction based oligonucleotide approach with HLA-DR4 subtyping using an amplification refractory mutation system RFLP technique. RESULTS: The risk of RA in those carrying a single shared epitope (SE) allele was 4 times, and in those carrying 2 SE alleles, 8 times that in the SE negative individuals. This increase was highest in individuals carrying 2 different SE alleles, with the risk in *0401/*0404 cases being 26 times higher. This genotype was associated with a 90-fold increased risk in men and this was more than doubled when age at disease onset was below 30. In all patients with RA, this genotype was associated with a substantially increased risk of being rheumatoid factor positive and having subcutaneous nodules and/or radiological erosion. CONCLUSION: Possession of the HLA-DRB1*0401/*0404 genotype carries a substantially high risk for RA development specifically in its more severe forms. The risks are particularly increased in young men.

"Homozygosity" for the HLA-DR shared epitope contributes the highest risk for rheumatoid arthritis concordance in identical twins.

OBJECTIVE: To assess the contribution of HLA-DRB1 alleles in determining rheumatoid arthritis (RA) concordance in monozygotic twins. METHODS: Ninety-one monozygotic twins pairs in which at least 1 twin was affected were typed for HLA-DRB1 using both serologic methods and polymerase chain reaction amplification with sequence-specific oligonucleotide hybridization. The role of DR4 and of the shared epitope in disease concordance was investigated. Relative risks (RR) with 95% confidence intervals were determined. RESULTS: Increased concordance for RA was observed in both DR4 positive and shared epitope positive pairs (RR 3.4 and 3.7, respectively). A 5-fold risk for RA concordance was seen in twins who were "homozygous" for the shared epitope, compared with those negative for the shared epitope. CONCLUSION: In the absence of the shared epitope, RA concordance in monozygotic twins is rare. In contrast, "homozygosity" for the shared epitope is the most important factor in determining RA concordance.

HLA allele detection using molecular techniques.

There are now many molecular biological techniques available to define HLA class I and class II alleles. Some of these are also applicable to other human polymorphic genes, in particular to those non-HLA genes encoded within the Mhc. The range of techniques available allows laboratories to choose those most suited to their purpose. The routine laboratory supporting solid organ transplants will need to type large numbers of potential recipients over a period of time, probably using PCR-SSOP while donors will be typed singly and rapidly using PCR-SSP with HLA allele compatibility determined by heteroduplex analysis. Laboratories supporting bone marrow transplantation, where time is less pressing, can choose from the whole range of techniques to determine accurately donor recipient Mhc compatibility. For disease studies, techniques defining precise HLA allele sequence polymorphisms are needed and high sample numbers have to be accommodated. When an association is established allele sequencing has to be used. In the near future, the precise role of HLA alleles in transplantation and disease susceptibility is likely to be established unambiguously.

Multiplex ARMS-RFLP: a simple and rapid method for HLA-DR4 subtyping.

We have developed a simple and rapid non-radioactive technique for HLA-DR4 subtyping. A multiplex ARMS-RFLP (Amplification Refractory Mutation System--Restriction Fragment Length Polymorphism) system allows HLA-DR4 subtyping by analysis of the products of two multiplex ARMS reaction mixtures. For some cases, restriction enzyme digests (Hae II and/or SacII) of the products are analysed. The technique relies on the fact that an ARMS primer with a mismatch at its 3'-end with respect to the template will not be elongated under PCR conditions. Hence, by designing ARMS primers such that different HLA-DR4 alleles yield PCR products of different lengths, only two reactions, each using a mixture of different ARMS primers, are sufficient to type all of the known HLA-DR4 alleles. This system can distinguish between HLA-DR4 'homozygotes' and 'heterozygotes' since every HLA-DR4 allele can be detected. The ARMS conditions were optimized using DNA from cell lines. This technique has now been used to type a panel of rheumatoid arthritis patients and controls.