Decreased Expression In NF-κB Essential Modulator Due to a Novel Splice-Site Mutation Causes Ectodermal Dysplasia with Immunodeficiency

X-linked ectodermal dysplasia with immunodeficiency (XL-EDA-ID) is caused by hypomorphic mutations in the nuclear factor κB (NF-κB) essential modulator (NEMO) gene, also called IKBKG, and these mutations impair but do not abolish NF-κB signaling, resulting in distinct clinical and immunologic phenotypes. We presented the patient with XL-EDA-ID showing a novel splice-site mutation. In this report we precisely study the involvement of this mutation in the molecular pathogenesis of XL-EDA-ID.

The patient is 12 years old Japanese boy. He had conical-shaped teeth and hypodontia. He had suffered from recurrent bacterial infections and these pathogenic bacteria were mostly streptococcus pneumonia. The laboratory examination revealed that the number of white blood cell counts, the classification of lymphocytes, and the serum immunoglobulin levels were within normal range. However the specific antibodies against measles and streptococcus pneumonia were negative in spite of these infections.

We identified a novel hemizygous mutation, 769-1 G>C, at the splicing acceptor site of exon 7 in the IKBKG gene. In order to clarify the effect of this mutation on mRNA, we performed a cloning analysis. Although various abnormal spliced NEMO (mutant NEMO) mRNAs were observed, a small amount of wild-type NEMO (WT NEMO) mRNA was also identified. The rate of WT and mutant was variable on the time of blood collection. Further we performed FACS and immunoblot analysis in order to evaluate the effect of this mutation at protein level. Two major bands which were presumed to be derived from WT and one mutant were detected in immunoblots using EBV transfected B cells, however the expression levels of these bands were markedly decreased compared to those of the healthy controls. The NEMO protein expression was confirmed to be decreased in various lineages of leukocytes. We generated WT and two representative mutant NEMO constructs and measured their NF-κB transcriptional activity using reporter assay. One mutant NEMO abolished NF-κB transcriptional activity, the other showed weak activity. However, neither of mutant NENO showed a dominant-negative effect against WT NEMO activity. CD14⁺ cells from the patient produced a lower level of TNF-α in response to IFN-γ stimulation, on the other hand CD3⁺ cells produced very little IFN-γ in response to IL-12. CD4⁺ T-cell proliferation was impaired in response to measles and mumps, but not rubella.

The hemizygous 769-1 G>C mutation was shown to cause the decreased expression of WT NEMO protein, resulting in the decrease in NF-κB activation and the development of XL-EDA-ID.

No relevant conflicts of interest to declare.