Large deletions and point mutations involving the dedicator of cytokinesis 8 (DOCK8) in the autosomal-recessive form of hyper-IgE syndrome

Background

The genetic etiologies of the hyper-IgE syndromes are diverse. Approximately 60% to 70% of patients with hyper-IgE syndrome have dominant mutations in STAT3, and a single patient was reported to have a homozygous TYK2 mutation. In the remaining patients with hyper-IgE syndrome, the genetic etiology has not yet been identified.

Objectives

We aimed to identify a gene that is mutated or deleted in autosomal recessive hyper-IgE syndrome.

Methods

We performed genome-wide single nucleotide polymorphism analysis for 9 patients with autosomal-recessive hyper-IgE syndrome to locate copy number variations and homozygous haplotypes. Homozygosity mapping was performed with 12 patients from 7 additional families. The candidate gene was analyzed by genomic and cDNA sequencing to identify causative alleles in a total of 27 patients with autosomal-recessive hyper-IgE syndrome.

Results

Subtelomeric biallelic microdeletions were identified in 5 patients at the terminus of chromosome 9p. In all 5 patients, the deleted interval involved dedicator of cytokinesis 8 (DOCK8), encoding a protein implicated in the regulation of the actin cytoskeleton. Sequencing of patients without large deletions revealed 16 patients from 9 unrelated families with distinct homozygous mutations in DOCK8 causing premature termination, frameshift, splice site disruption, and single exon deletions and microdeletions. DOCK8 deficiency was associated with impaired activation of CD4⁺ and CD8⁺T cells.

Conclusion

Autosomal-recessive mutations in DOCK8 are responsible for many, although not all, cases of autosomal-recessive hyper-IgE syndrome. DOCK8 disruption is associated with a phenotype of severe cellular immunodeficiency characterized by susceptibility to viral infections, atopic eczema, defective T-cell activation and Th17 cell differentiation, and impaired eosinophil homeostasis and dysregulation of IgE.

Key words: Autosomal recessive hyper-IgE syndrome, human gene mutation, DOCK8, primary immunodeficiency, molluscum contagiosum, recurrent infection, T cells, TH17 cells, eosinophils, IgE regulation, copy number variations, genomic deletions

Abbreviations used: AR, Autosomal-recessive, CFSE, Carboxyfluorescein succinimidyl ester, CNV, Copy number variation, DHR, Dedicator of cytokinesis homology region, DOCK, Dedicator of cytokinesis, GEF, Guanine nucleotide exchange factor, HIES, Hyper-IgE syndrome, NIH, National Institutes of Health, NK, Natural killer, STAT3, Signal transducer and activator of transcription 3, WASP, Wiskott-Aldrich syndrome protein