In hyper-IgE syndromes (HIES), a group of primary immunodeficiencies clinically overlapping with atopic dermatitis, early diagnosis is crucial to initiate appropriate therapy and prevent irreversible complications. Identification of underlying gene defects such as in DOCK8 and STAT3 and corresponding molecular testing has improved diagnosis. Yet, in a child and her newborn sibling with HIES phenotype molecular diagnosis was misleading. Extensive analyses driven by the clinical phenotype identified an intronic homozygous DOCK8 variant c.4626 + 76 A > G creating a novel splice site as disease-causing. While the affected newborn carrying the homozygous variant had no expression of DOCK8 protein, in the index patient molecular diagnosis was compromised due to expression of altered and wildtype DOCK8 transcripts and DOCK8 protein as well as defective STAT3 signaling. Sanger sequencing of lymphocyte subsets revealed that somatic alterations and reversions revoked the predominance of the novel over the canonical splice site in the index patient explaining DOCK8 protein expression, whereas defective STAT3 responses in the index patient were explained by a T cell phenotype skewed towards central and effector memory T cells. Hence, somatic alterations and skewed immune cell phenotypes due to selective pressure may compromise molecular diagnosis and need to be considered with unexpected clinical and molecular findings.

This work was supported by the Wilhelm-Sander foundation (2013.015.2), the German Research Foundation (DFG RE2799/6-1), the Fritz-Bender foundation (all to E.D.R.), the EU Horizon2020 Collaborative Research Project SOUND (633974) (to J.G.), and the Spanish Ministry of Economy and Competitiveness, Centro de Excelencia Severo Ochoa, and to the EMBL partnership and of the CERCA Programme/Generalitat de Catalunya. Data included in this publication are part of a medical thesis at the School of Medicine, LMU Munich (B.D.S.).