A deep intronic splice mutation of STAT3 underlies hyper IgE syndrome by negative dominance

Heterozygous in-frame mutations in coding regions of human STAT3 underlie the only known autosomal dominant form of hy- per IgE syndrome (AD HIES). About 5% of familial cases remain unexplained. The mutant proteins are loss-of-function and dominant-negative when tested following overproduction in re- cipient cells. However, the production of mutant proteins has not been detected and quantified in the cells of heterozygous pa- tients. We report a deep intronic heterozygous STAT3 mutation, c.1282-89C>T, in 7 relatives with AD HIES. This mutation creates a new exon in the STAT3 complementary DNA, which, when over- expressed, generates a mutant STAT3 protein (D427ins17) that is loss-of-function and dominant-negative in terms of tyrosine phos- phorylation, DNA binding, and transcriptional activity. In immor- talized B cells from these patients, the D427ins17 protein was 2 kDa larger and 4-fold less abundant than wild-type STAT3, on mass spectrometry. The patients' primary B and T lymphocytes responded poorly to STAT3-dependent cytokines. These findings are reminiscent of the impaired responses of leukocytes from other patients with AD HIES due to typical STAT3 coding muta- tions, providing further evidence for the dominance of the mutant intronic allele. These findings highlight the importance of sequenc- ing STAT3 introns in patients with HIES without candidate variants in coding regions and essential splice sites. They also show that AD HIES-causing STAT3 mutant alleles can be dominant-negative even if the encoded protein is produced in significantly smaller amounts than wild-type STAT3. Overall design: Examination of gene expression in EBV-B cells from healthy subjects and AD HIES patients stimulated with IL-21, IL-6, IL-23, IL-10, and IFNa