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

Clinical findings in patients with DOCK8 mutations. A-C, Severe molluscum contagiosum burden of patient ARH014. H, Molluscum infection of patient ARH012. D-F, Severe dermatitis in patients ARH010.8 and ARH010.9. G, Severe oral papilloma virus infection of patient ARH009. I (MRI) and J (diffusion scan) document the cause of death in patient ARH003, who developed an undefined form of encephalitis.

A, Representational oligonucleotide microarray analysis data demonstrating copy number abnormalities consistent with subtelomeric deletions of 9p in AR-HIES. Individuals ARH001 to ARH004 have homozygous deletions, ARH005 has a compound heterozygous deletion, and ARH006 has a heterozygous deletion. The remaining subjects do not have demonstrable deletions. Genome-wide single nucleotide polymorphism Nsp 250k arrays were used for subjects ARH001 to ARH009. B, Deletions and homozygous intervals and known and predicted genes at the terminus of chromosome 9p for patients with HIES. C9orf66 is an open reading frame, and FAM138C is a noncoding RNA gene. FOXD4 is a transcription factor, and CBWD has a cobalamin binding domain and nuclease function. DOCK8 is described in the text.

Exonic deletions in DOCK8. Pedigrees (A, C, E). Squares, males; circles, females. Filled symbols, patients; slashes, deceased individuals. The lack of PCR products from patients' DNA compared with control DNA suggests exonic deletions (B, D, F). cntrl, Control.

Mutations in DOCK8. Pedigrees (A, D, I, L, O, Q). Squares, males; circles, females. Filled symbols, patients; slashes, deceased individuals. Point mutations in the splice site (B, P) or within exons (E, J). Stop codon caused by point mutation (K) or frameshift (H, M). Generation of a cryptic splice site leading to a 4-bp deletion (F, G). Exon skipping shown by cDNA sequencing (C, M, S) and PCR (C, R). Lack of PCR products from genomic DNA suggesting exonic deletions (N, R).

Cartoon showing the predicted impact of the mutations on DOCK8 protein expression. In 3 families, the mutation results in a truncated protein affecting both DHR domains, whereas in 2 families, the truncated protein lacks the DHR-1 domain. In family ARH009, 53 amino acids are missing within the DHR-2 domain, and in family ARH0010, 50 amino acids are missing in between the 2 DHR domains. In family ARH013, DOCK8 is truncated at the C-terminus.

DOCK8 deficiency impairs T-cell activation. A, DOCK8 protein expression in probands, family members, and control samples. Lysates from PBMCs, normalized for protein content, were analyzed by immunoblotting with an anti-human DOCK8 antibody. A dominant band of about 180 Kilo Dalton (arrowhead) and several smaller isoforms were detected in control and family members samples but not in those of the probands. As loading control, the blots were re-probed with an anti-human Tubulin antibody. B, Proliferative responses of PBMCs to anti-CD3 mAb treatment (n = 2-5/group; ^∗P = .02). C, DOCK8 deficiency impairs the activation of both CD4⁺ and CD8⁺ T cells. PBMCs were loaded with CFSE and stimulated with anti-CD3 + anti-CD28 mAb for 3 days. Gated populations of mAb-stimulated CD3⁺, CD4⁺, and CD8⁺ T cells were analyzed for CFSE fluorescence intensity (solid lines) and compared with the respective unstimulated cell population (shaded area). CNTL, Control.

Hypothetical function of DOCK8. DOCK8 is likely to function as a GEF for the Rho-GTPases Cdc42 and Rac1, turning them into the active, GTP-bound form on receptor engagement (eg, receptor tyrosine kinases, antigen receptors, and adhesion receptors). An unknown protein possibly stabilizes the interaction of DOCK8 with Cdc42 and Rac1. GTPase activation induces dynamic filamentous actin rearrangements and lamellipodia formation, possibly via WASP, leading to cell growth, migration, and adhesion. Given the clinical phenotype of the AR-HIES patients with DOCK8 deficiency, we propose an important role of DOCK8 in T-cell actin dynamics, which might be important for the formation of the immunologic synapse, leading to T-cell activation, proliferation, and differentiation. TCR, T-cell receptor.

PCR identification of homozygous deletions affecting DOCK8 in patients with AR-HIES with CNV abnormalities at 9p. A, The deletion in ARH002 ends between E25 and E26, whereas that of ARH003 ends between E32 and E33. B, The deletion in ARH001 ends between E3 and E4. All 3 deletions were found to extend proximally beyond exon 1, but their precise 5′’ edges have not been established. Note that ARH006, who has a heterozygous deletion at 9p, successfully amplifies the respective exons, as would be expected given his possession of an undeleted copy of DOCK8. CNTL, Control.

Heritability of copy loss in 4 families with AR-HIES. ARH004 shows typical mendelian inheritance of a deletion. ARH006 demonstrates partial repair of the CNV, presumably by gene conversion.^E6 ARH001 shows a de novo homozygous deletion. Parentage for ARH001 was confirmed by SNP inheritance. No mendelian errors were found in 44,645 genotypes surveyed. ARH007 is a patient without a deletion but with extensive homozygosity at this locus.