Molecular analysis of the genetic defect in a large cohort of IP patients and identification of novel NEMO mutations interfering with NF-κB activation

Institute of Genetics and Biophysics, Adriano Buzzati Traverso-CR, Naples, Italy.
Human Molecular Genetics (Impact Factor: 6.39). 08/2004; 13(16):1763-73. DOI: 10.1093/hmg/ddh192
Source: PubMed


Incontinentia Pigmenti (IP) is an X-linked genodermatosis that is lethal for males and present in females with abnormal skin pigmentation and high variable clinical signs, including retinal detachment, anodontia, alopecia, nail dystrophy and nervous system defects. The NF-kappaB essential modulator (NEMO) gene, responsible for IP, encodes the regulatory subunit of the IkappaB kinase (IKK) complex required for nuclear factor kappaB (NF-kappaB) activation. We analyzed the NEMO gene in 122 IP patients and identified mutations in 83 (36 familiar and 47 sporadic cases). The recurrent NEMO exon 4-10 deletion that is the major cause of the disease was present in 73 females (59.8%). In addition 10 point alterations (8.2% of females) were identified: three frameshift, three nonsense, three missense and one in-frame deletion of a single amino acid. We measured the effects of these NEMO point-mutations on NF-kappaB signaling in nemo(-/-) deficient murine pre-B cells. A mutation in the N-terminal domain, required for IKK assembly, reduced but did not abolish NF-kappaB activation following lipopolysaccharide stimulation. Mutations that disrupt the C-terminal domain, required for the recruitment of upstream factors, showed lower or no NF-kappaB activation. A phenotype score based on clinical features of our IP patients was applied for summarizing disease severity. The score did not correlate with mutation type or domain affected indicating that other factors influence the severity of IP. Such a factor is likely to be X-inactivation. Indeed, 64% of our patients have extremely skewed X-inactivation pattern (>/=80 : 20). Overall IP pathogenesis thus depends on a combination of X-inactivation and protein domain that recruit upstream factors and activate NF-kappaB.

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    • "IP has also been diagnosed in males with a 47,XXY karyotype (Klinefelter syndrome) [19]. The large heterogeneity of defects, the severe clinical presentations, and the wide spectrum of IKBKG/NEMO alterations [7,11,14,20] makes the selection of homogeneous groups of patients difficult, precluding any therapeutic approaches. Indeed, despite the considerable progress that has been made in detailing the basic pathology of the IP disorder, the gap between research and clinical care has remained wide. "
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    ABSTRACT: We report here on the building-up of a database of information related to 386 cases of Incontinentia Pigmenti collected in a thirteen-year activity (2000-2013) at our centre of expertise. The database has been constructed on the basis of a continuous collection of patients (27.6/year), the majority diagnosed as sporadic cases (75.6%). This activity has generated a rich source of information for future research studies by integrating molecular/clinical data with scientific knowledge. We describe the content, architecture and future utility of this collection of data on IP to offer comprehensive anonymous information to the international scientific community.
    Orphanet Journal of Rare Diseases 06/2014; 9(1):93. DOI:10.1186/1750-1172-9-93 · 3.36 Impact Factor
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    • "p.Arg173GlyfsX108 Exon 4 Frameshift ND IP [Aradhya et al., 2001c] 17 c.518+2T>A ND Intron 4 Splice site ND IP [Aradhya et al., 2001c] 18 c.523dup p.Arg175ProfsX13 Exon 5 Frameshift ND IP [Aradhya et al., 2001c] 19 c.G549C p.Gln183His Exon 5 Missense S IP [Hsiao et al., 2010] 20 c.551 588del p.Leu184ArgfsX57 Exon 5 Frameshift ND IP [Aradhya et al., 2001c] 21 c.570del p.Leu191CysfsX90 Exon 5 Frameshift ND IP [Aradhya et al., 2001c] 22 c.638 642dup p.Met215SerfsX68 Exon 5 Frameshift ND IP [Aradhya et al., 2001c] 23 c.639 645del p.Arg214SerfsX65 Exon 5 Frameshift ND IP [Aradhya et al., 2001c] 24 c.662C>A p.Ser221X Exon 5 Nonsense ND IP [Fusco et al., 2008] 25 c.706C>T p.Gln236X Exon 6 Nonsense S IP [Aradhya et al., 2001c] 26 c.715C>T p.Gln239X Exon 6 Nonsense S IP [Fusco et al., 2004] 27 c.723C>G p.Tyr241X Exon 6 Nonsense ND IP [Aradhya et al., 2001c] 28 c.766C>T p.Arg256X Exon 6 Nonsense F IP [Fusco et al., 2008] 29 c.792dup p.Gln265ThrfsX19 Exon 7 Frameshift S IP [Martinez-Pomar et al., 2005]. 30 c.868C>T p.Gln290 X Exon 7 Nonsense ND IP [Aradhya et al., 2001c] "
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    ABSTRACT: Incontinentia pigmenti (IP) is an X-linked-dominant Mendelian disorder caused by mutation in the IKBKG/NEMO gene, encoding for NEMO/IKKgamma, a regulatory protein of nuclear factor kappaB (NF-kB) signaling. In more than 80% of cases, IP is due to recurrent or nonrecurrent deletions causing loss-of-function (LoF) of NEMO/IKKgamma. We review how the local architecture of the IKBKG/NEMO locus with segmental duplication and a high frequency of repetitive elements favor de novo aberrant recombination through different mechanisms producing genomic microdeletion. We report here a new microindel (c.436_471delinsT, p.Val146X) arising through a DNA-replication-repair fork-stalling-and-template-switching and microhomology-mediated-end-joining mechanism in a sporadic IP case. The LoF mutations of IKBKG/NEMO leading to IP include small insertions/deletions (indel) causing frameshift and premature stop codons, which account for 10% of cases. We here present 21 point mutations previously unreported, which further extend the spectrum of pathologic variants: 14/21 predict LoF because of premature stop codon (6/14) or frameshift (8/14), whereas 7/21 predict a partial loss of NEMO/IKKgamma activity (two splicing and five missense). We review how the analysis of IP-associated IKBKG/NEMO hypomorphic mutants has contributed to the understanding of the pathophysiological mechanism of IP disease and has provided important information on affected NF-kB signaling. We built a locus-specific database listing all IKBKG/NEMO variants, accessible at
    Human Mutation 02/2014; 35(2). DOI:10.1002/humu.22483 · 5.14 Impact Factor
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    • "Highly skewed inactivation pattern has been observed in patients with gene mutations within the Xq28 region due to negative cell selection. For example, skewed inactivation has been reported in rearrangement and truncation mutations that result in a loss of function in the NEMO (IKBKG) gene, which is associated with incontinentia pigmenti, hypohidrotic ectodermal dysplasia, and other types of immunodeficiencies [20-22]. In our patient, negative selection of cells expressing the mutant NEMO allele on the deleted X-chromosome may then result in the highly skewed X-inactivation; however, this alone cannot explain her clinical phenotype. "
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    ABSTRACT: Background Global developmental delay and mental retardation are associated with X-linked disorders including Hunter syndrome (mucopolysaccharidosis type II) and Fragile X syndrome (FXS). Single nucleotide mutations in the iduronate 2-sulfatase (IDS) gene at Xq28 most commonly cause Hunter syndrome while a CGG expansion in the FMR1 gene at Xq27.3 is associated with Fragile X syndrome. Gene deletions of the Xq27-28 region are less frequently found in either condition with rare reports in females. Additionally, an association between Xq27-28 deletions and skewed X-inactivation of the normal X chromosome observed in previous studies suggested a primary role of the Xq27-28 region in X-inactivation. Case presentation We describe the clinical, molecular and biochemical evaluations of a four year-old female patient with global developmental delay and a hemizygous deletion of Xq27.3q28 (144,270,614-154,845,961 bp), a 10.6 Mb region that contains >100 genes including IDS and FMR1. A literature review revealed rare cases with similar deletions that included IDS and FMR1 in females with developmental delay, variable features of Hunter syndrome, and skewed X-inactivation of the normal X chromosome. In contrast, our patient exhibited skewed X-inactivation of the deleted X chromosome and tested negative for Hunter syndrome. Conclusions This is a report of a female with a 10.6 Mb Xq27-28 deletion with skewed inactivation of the deleted X chromosome. Contrary to previous reports, our observations do not support a primary role of the Xq27-28 region in X-inactivation. A review of the genes in the deletion region revealed several potential genes that may contribute to the patient’s developmental delays, and sequencing of the active X chromosome may provide insight into the etiology of this clinical presentation.
    BMC Medical Genetics 05/2013; 14(1):49. DOI:10.1186/1471-2350-14-49 · 2.08 Impact Factor
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