Genome-wide association study of body mass index in 23 000 individuals with and without asthma

BACKGROUND

Both asthma and obesity are complex disorders that are influenced by environmental and genetic factors. Shared genetic factors between asthma and obesity have been proposed to partly explain epidemiological findings of co-morbidity between these conditions.

OBJECTIVE

To identify genetic variants that are associated with body mass index (BMI) in asthmatic children and adults, and to evaluate if there are differences between the genetics of BMI in asthmatics and healthy individuals.

METHODS

In total, 19 studies contributed with genome-wide analysis study (GWAS) data from more than 23 000 individuals with predominantly European descent, of whom 8165 are asthmatics.

RESULTS

We report associations between several DENND1B variants (P = 2.2 × 10(-7) for rs4915551) on chromosome 1q31 and BMI from a meta-analysis of GWAS data using 2691 asthmatic children (screening data). The top DENND1B single nucleotide polymorphisms(SNPs) were next evaluated in seven independent replication data sets comprising 2014 asthmatics, and rs4915551 was nominally replicated (P < 0.05) in two of the seven studies and of borderline significance in one (P = 0.059). However, strong evidence of effect heterogeneity was observed and overall, the association between rs4915551 and BMI was not significant in the total replication data set, P = 0.71. Using a random effects model, BMI was overall estimated to increase by 0.30 kg/m(2) (P = 0.01 for combined screening and replication data sets, N = 4705) per additional G allele of this DENND1BSNP. FTO was confirmed as an important gene for adult and childhood BMI regardless of asthma status.

CONCLUSIONS AND CLINICAL RELEVANCE

DENND1B was recently identified as an asthma susceptibility gene in a GWAS on children, and here, we find evidence that DENND1B variants may also be associated with BMI in asthmatic children. However, the association was overall not replicated in the independent data sets and the heterogeneous effect of DENND1B points to complex associations with the studied diseases that deserve further study.

Expression of the peptide C4b-binding protein beta in the arthritic joint

BACKGROUND

C4b-binding protein (C4BP) is a plasma oligomeric glycoprotein that participates in the regulation of complement and haemostasis. Complement-regulatory activity depends on the C4BPalpha-polypeptide, whereas the C4BPbeta-polypeptide inactivates protein S, interfering with the anti-coagulatory protein C-dependent pathway.

OBJECTIVE

To investigate the expression of C4BPbeta in the rheumatoid joint.

METHODS

Expression of C4BP was studied in synovial explants from patients with rheumatoid arthritis, osteoarthritis and healthy controls, using immunohistochemistry and in situ hybridisation. C4BP isoforms and free C4BPbeta were studied in synovial effusions from patients with rheumatoid arthritis, osteoarthritis and microcrystalline arthritis (MCA) by immunoblotting; total and free protein S levels were studied by enzyme immunoassay.

RESULTS

C4BPbeta was overexpressed in the synovial membranes of patients with rheumatoid arthritis, in close association with the severity of synovitis and the extension of interstitial fibrin deposits. As many as 85% fluids from patients with rheumatoid arthritis contained free C4BPbeta, whereas this unusual polypeptide was present in 50% fluids from patients with MCA and 40% fluids from patients with osteoarthritis. Free protein S at the effusions was pathologically reduced in patients with rheumatoid arthritis and MCA, and remained normal in patients with osteoarthritis.

CONCLUSION

C4BPbeta is expressed by the inflamed synovial tissue, where it can participate in processes of tissue remodelling associated with invasive growth.

Functional analysis of MCCA and MCCB mutations causing methylcrotonylglycinuria

Methylcrotonylglycinuria (MCG; MIM 210200) is an autosomal recessive inherited human disorder caused by the deficiency of 3-methylcrotonyl-CoA carboxylase (MCC, E.C.6.4.1.4), involved in leucine catabolism. This mitochondrial enzyme is one of the four biotin-dependent carboxylases known in humans. MCC is composed of two different types of subunits, alpha and beta, encoded by the nuclear genes MCCA and MCCB, respectively, recently cloned and characterized. Several mutations have been identified, in both genes, the majority are missense mutations along with splicing mutations and small insertions/deletions. We have expressed four missense mutations, two MCCA and two MCCB mapping to highly evolutionarily conserved residues, by transient transfection of SV40-transformed deficient fibroblasts in order to confirm their pathogenic effect. All the missense mutations expressed resulted in null or severely diminished MCC activity providing direct evidence that they are disease-causing ones. The MCCA mutations have been analysed in the context of three-dimensional structural information modelling the changes in the crystallized biotin carboxylase subunit of the Escherichia coli acetyl-CoA carboxylase. The apparent severity of all the MCC mutations contrasts with the variety of the clinical phenotypes suggesting that there are other cellular and metabolic unknown factors that affect the resulting phenotype.