A deep intronic splice mutation of <i>STAT3</i> underlies hyper IgE syndrome by negative dominance

Abstract

Heterozygous in-frame mutations in coding regions of human <i>STAT3</i> underlie the only known autosomal dominant form of hyper 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 recipient cells. However, the production of mutant proteins has not been detected and quantified in the cells of heterozygous patients. We report a deep intronic heterozygous <i>STAT3</i> mutation, c.1282-89C>T, in 7 relatives with AD HIES. This mutation creates a new exon in the <i>STAT3</i> complementary DNA, which, when overexpressed, generates a mutant STAT3 protein (D427ins17) that is loss-of-function and dominant-negative in terms of tyrosine phosphorylation, DNA binding, and transcriptional activity. In immortalized 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 <i>STAT</i>3 coding mutations, providing further evidence for the dominance of the mutant intronic allele. These findings highlight the importance of sequencing <i>STAT3</i> introns in patients with HIES without candidate variants in coding regions and essential splice sites. They also show that AD HIES-causing <i>STAT3</i> mutant alleles can be dominant-negative even if the encoded protein is produced in significantly smaller amounts than wild-type STAT3.