Dysgammaglobulinemia Associated With Glu349del, a Hypomorphic XIAP Mutation

BACKGROUND

X-linked lymphoproliferative syndrome type 2 is a rare hereditary immunodeficiency caused by mutations in the XIAP gene. This immunodeficiency frequently results in hemophagocytic lymphohistiocytosis, although hypogammaglobulinemia and dysgammaglobulinemia are also common.

OBJECTIVE

We identified 17 patients from 12 Japanese families with mutations in XIAP. The Glu349del mutation was observed in 3 patients, each from a different family. Interestingly, these patients exhibited dysgammaglobulinemia but not hemophagocytic lymphohistiocytosis. We conducted an immunological study of patients carrying Glu349del and other mutations to elucidate the pathogenic mechanisms of dysgammaglobulinemia in patients with mutations in the XIAP gene.

PATIENTS AND METHODS

We performed an immunological study of 2 patients carrying the Glu349del mutation and 8 patients with other mutations.

RESULTS

Flow cytometry showed that the percentage of memory B cells in patients with a mutation in XIAP was lower than that observed in the healthy controls. The patients with the Glu349del mutation had a lower percentage of memory B cells than those with other mutations. Ig production was reduced in patients with the Glu349del mutation. Increased susceptibility to apoptosis was observed in the patients with other mutations. Susceptibility to apoptosis was normal in patients with Glu349del. Microarray analysis indicated that expression of Ig-related genes was reduced in patients with the Glu349del mutation and that the pattern was different from that observed in the healthy controls or patients with other mutations in XIAP.

CONCLUSIONS

Patients carrying the Glu349del mutation in the XIAP gene may have a clinically and immunologically distinct phenotype from patients with other XIAP mutations. The Glu349del mutation may be associated with dysgammaglobulinemia.

Functional variants in the thromboxane A2 receptor gene are associated with lung function in childhood-onset asthma

BACKGROUND

The thromboxane A2 receptor (TBXA2R) gene is associated with asthma, but no functional genetic variations are known to associate with the disease or its related phenotypes.

OBJECTIVE

To investigate the association of TBXA2R polymorphisms with asthma susceptibility and related phenotypes and to identify functionally relevant polymorphisms.

METHODS

We performed comprehensive sequencing of the TBXA2R gene in 48 Japanese control subjects and found a set of variants (SNP1 G>T rs2238634, SNP2 T>G rs2238633, SNP3 C>T rs2238632 and SNP4 G>A rs2238631) in intron 1 in linkage disequilibrium with c.795 T>C rs1131882, which was previously reported to be associated with asthma and related phenotypes. To investigate the effect of four common haplotypes (H1, H2, H3 and H4) on transcriptional activity, we performed a luciferase assay in primary bronchial smooth muscle cells (BSMCs) and human airway epithelial cells (BEAS-2B). We also studied the haplotype association with lung function, TBXA2R mRNA levels, and eosinophil fraction/count in peripheral blood in childhood-onset asthma patients and/or controls.

RESULTS

H2 and H4, containing minor alleles of SNP2 and SNP3, had significantly higher transcriptional activities than H1 consisting of major alleles (P < 0.001 in BSMCs and BEAS-2B). Homozygotes for redefined haplotype h2 corresponding to minor alleles of SNP2 and SNP3 were associated with lower lung function in childhood-onset asthma patients compared to other zygotes (baseline Forced expiratory volume in one second (FEV1)/ Forced vital capacity (FVC) and Forced expiratory flow between 25% and 75% of the FVC (%FEF(25-75%)): P = 0.00201 and 0.0128, respectively, and post-bronchodilator FEV1/FVC and %FEF(25-75%): P = 0.00224 and 0.0393 respectively). Haplotype h2 was also associated with higher mRNA levels in control peripheral blood cells and higher blood eosinophil fractions and counts in female controls.

CONCLUSIONS AND CLINICAL RELEVANCE

Genetic variants were identified in the TBXA2R gene that influenced transcriptional activity and were associated with asthma-related phenotypes. Thromboxane pathways may therefore play important roles in airway inflammation and remodelling in asthma patients.