Asma Smahi

TLR3 Deficiency in Patients with Herpes Simplex Encephalitis

Some Toll and Toll-like receptors (TLRs) provide immunity to experimental infections in animal models, but their contribution to host defense in natural ecosystems is unknown. We report a dominant-negative TLR3 allele in otherwise healthy children with herpes simplex virus 1 (HSV-1) encephalitis. TLR3 is expressed in the central nervous system (CNS), where it is required to control HSV-1, which spreads from the epithelium to the CNS via cranial nerves. TLR3 is also expressed in epithelial and dendritic cells, which apparently use TLR3-independent pathways to prevent further dissemination of HSV-1 and to provide resistance to other pathogens in TLR3-deficient patients. Human TLR3 appears to be redundant in host defense to most microbes but is vital for natural immunity to HSV-1 in the CNS, which suggests that neurotropic viruses have contributed to the evolutionary maintenance of TLR3.

X-linked anhidrotic ectodermal dysplasia with immunodeficiency is caused by impaired NF-kappaB signaling.

The molecular basis of X-linked recessive anhidrotic ectodermal dysplasia with immunodeficiency (EDA-ID) has remained elusive. Here we report hypomorphic mutations in the gene IKBKG in 12 males with EDA-ID from 8 kindreds, and 2 patients with a related and hitherto unrecognized syndrome of EDA-ID with osteopetrosis and lymphoedema (OL-EDA-ID). Mutations in the coding region of IKBKG are associated with EDA-ID, and stop codon mutations, with OL-EDA-ID. IKBKG encodes NEMO, the regulatory subunit of the IKK (IκB kinase) complex, which is essential for NF-κB signaling. Germline loss-of-function mutations in IKBKG are lethal in male fetuses. We show that IKBKG mutations causing OL-EDA-ID and EDA-ID impair but do not abolish NF-κB signaling. We also show that the ectodysplasin receptor, DL, triggers NF-κB through the NEMO protein, indicating that EDA results from impaired NF-κB signaling. Finally, we show that abnormal immunity in OL-EDA-ID patients results from impaired cell responses to lipopolysaccharide, interleukin (IL)-1β, IL-18, TNFα and CD154. We thus report for the first time that impaired but not abolished NF-κB signaling in humans results in two related syndromes that associate specific developmental and immunological defects.

Interleukin-36-Receptor Antagonist Deficiency and Generalized Pustular Psoriasis

BACKGROUND Generalized pustular psoriasis is a life-threatening disease of unknown cause. It is characterized by sudden, repeated episodes of high-grade fever, generalized rash, and disseminated pustules, with hyperleukocytosis and elevated serum levels of C-reactive protein, which may be associated with plaque-type psoriasis. METHODS We performed homozygosity mapping and direct sequencing in nine Tunisian multiplex families with autosomal recessive generalized pustular psoriasis. We assessed the effect of mutations on protein expression and conformation, stability, and function. RESULTS We identified significant linkage to an interval of 1.2 megabases on chromosome 2q13-q14.1 and a homozygous missense mutation in IL36RN, encoding an interleukin-36-receptor antagonist (interleukin-36Ra), an antiinflammatory cytokine. This mutation predicts the substitution of a proline residue for leucine at amino acid position 27 (L27P). Homology-based structural modeling of human interleukin-36Ra suggests that the proline at position 27 affects both the stability of interleukin-36Ra and its interaction with its receptor, interleukin-1 receptor-like 2 (interleukin-1 receptor-related protein 2). Biochemical analyses showed that the L27P variant was poorly expressed and less potent than the nonvariant interleukin-36Ra in inhibiting a cytokine-induced response in an interleukin-8 reporter assay, leading to enhanced production of inflammatory cytokines (interleukin-8 in particular) by keratinocytes from the patients. CONCLUSIONS Aberrant interleukin-36Ra structure and function lead to unregulated secretion of inflammatory cytokines and generalized pustular psoriasis. (Funded by Agence Nationale de la Recherche and Société Française de Dermatologie.).

Only four genes (EDA1, EDAR, EDARADD, and WNT10A) account for 90% of hypohidrotic/anhidrotic ectodermal dysplasia cases.

Hypohidrotic and anhidrotic ectodermal dysplasia (HED/EDA) is a rare genodermatosis characterized by abnormal development of sweat glands, teeth, and hair. Three disease‐causing genes have been hitherto identified, namely, (1) EDA1 accounting for X‐linked forms, (2) EDAR, and (3) EDARADD, causing both autosomal dominant and recessive forms. Recently, WNT10A gene was identified as responsible for various autosomal recessive forms of ectodermal dysplasias, including onycho‐odonto‐dermal dysplasia (OODD) and Schöpf‐Schulz‐Passarge syndrome. We systematically studied EDA1, EDAR, EDARADD, and WNT10A genes in a large cohort of 65 unrelated patients, of which 61 presented with HED/EDA. A total of 50 mutations (including 32 novel mutations) accounted for 60/65 cases in our series. These four genes accounted for 92% (56/61 patients) of HED/EDA cases: (1) the EDA1 gene was the most common disease‐causing gene (58% of cases), (2)WNT10A and EDAR were each responsible for 16% of cases. Moreover, a novel disease locus for dominant HED/EDA mapped to chromosome 14q12–q13.1. Although no clinical differences between patients carrying EDA1, EDAR, or EDARADD mutations could be identified, patients harboring WNT10A mutations displayed distinctive clinical features (marked dental phenotype, no facial dysmorphism), helping to decide which gene should be first investigated in HED/EDA. Hum Mutat 31:1–8, 2010.

The NEMO mutation creating the most-upstream premature stop codon is hypomorphic because of a reinitiation of translation.

Amorphic mutations in the NF- kappa B essential modulator (NEMO) cause X-dominant incontinentia pigmenti, which is lethal in males in utero, whereas hypomorphic mutations cause X-recessive anhidrotic ectodermal dysplasia with immunodeficiency, a complex developmental disorder and life-threatening primary immunodeficiency. We characterized the NEMO mutation 110_111insC, which creates the most-upstream premature translation termination codon (at codon position 49) of any known NEMO mutation. Surprisingly, this mutation is associated with a pure immunodeficiency. We solve this paradox by showing that a Kozakian methionine codon located immediately downstream from the insertion allows the reinitiation of translation. The residual production of an NH(2)-truncated NEMO protein was sufficient for normal fetal development and for the subsequent normal development of skin appendages but was insufficient for the development of protective immune responses.

Alterations of the IKBKG Locus and Diseases: An Update and a Report of 13 Novel Mutations

Mutations in the inhibitor of kappa light polypeptide gene enhancer in B‐cells, kinase gamma (IKBKG), also called nuclear factor‐kappaB (NF‐kB) essential modulator (NEMO), gene are the most common single cause of incontinentia pigmenti (IP) in females and anhydrotic ectodermal dysplasia with immunodeficiency (EDA‐ID) in males. The IKBKG gene, located in the Xq28 chromosomal region, encodes for the regulatory subunit of the inhibitor of kappaB (IkB) kinase (IKK) complex required for the activation of the NF‐kB pathway. Therefore, the remarkably heterogeneous and often severe clinical presentation reported in IP is due to the pleiotropic role of this signaling transcription pathway. A recurrent exon 4_10 genomic rearrangement in the IKBKG gene accounts for 60 to 80% of IP‐causing mutations. Besides the IKBKG rearrangement found in IP females (which is lethal in males), a total of 69 different small mutations (missense, frameshift, nonsense, and splice‐site mutations) have been reported, including 13 novel ones in this work. The updated distribution of all the IP‐ and EDA‐ID‐causing mutations along the IKBKG gene highlights a secondary hotspot mutation in exon 10, which contains only 11% of the protein. Furthermore, familial inheritance analysis revealed an unexpectedly high incidence of sporadic cases (>65%). The sum of the observations can aid both in determining the molecular basis of IP and EDA‐ID allelic diseases, and in genetic counseling in affected families. Hum Mutat 29(5), 595–604, 2008.

Combination of Linkage Mapping and Microarray-Expression Analysis Identifies NF-κB Signaling Defect as a Cause of Autosomal-Recessive Mental Retardation

Autosomal-recessive inheritance accounts for nearly 25% of nonsyndromic mental retardation (MR), but the extreme heterogeneity of such conditions markedly hampers gene identification. Combining autozygosity mapping and RNA expression profiling in a consanguineous Tunisian family of three MR children with mild microcephaly and white-matter abnormalities identified the TRAPPC9 gene, which encodes a NF-kappaB-inducing kinase (NIK) and IkappaB kinase complex beta (IKK-beta) binding protein, as a likely candidate. Sequencing analysis revealed a nonsense variant (c.1708C>T [p.R570X]) within exon 9 of this gene that is responsible for an undetectable level of TRAPPC9 protein in patient skin fibroblasts. Moreover, TNF-alpha stimulation assays showed a defect in IkBalpha degradation, suggesting impaired NF-kappaB signaling in patient cells. This study provides evidence of an NF-kappaB signaling defect in isolated MR.

NEMO/IKKγ: linking NF-κB to human disease

Abstract Until recently, no genetic disease caused by NF-κB dysfunction was known. This changed with the identification of the X-linked gene encoding a molecule of the NF-κB signaling pathway, NEMO/IKKγ. Two distinct X-linked human diseases, incontinentia pigmenti (IP) and anhidrotic ectodermal dysplasia associated with immunodeficiency (EDA-ID), have been linked to NEMO/IKKγ dysfunction, providing a unique view of the role that NF-κB plays in human development, skin homeostasis and innate and acquired immunity.

First Clinical Description of an Infant With Interleukin-36-Receptor Antagonist Deficiency Successfully Treated With Anakinra

YM is the first son of Tunisian consanguineous parents who developed, at 2 weeks of life, an erythematous and scaly eruption, with subsequent rapid evolution toward generalized pustular psoriasis. Afterward, cutaneous flares of diffuse erythematous rash and pustules involving the whole body appeared, with a once weekly periodicity. Intense irritability was present during flares without fever. Moreover, since 1 month of age the infant presented with diarrhea, dysphagia, and reduced feeding rate, with failure to thrive. Laboratory tests during acute flares showed marked leukocytosis, thrombocytosis, and anemia without C-reactive protein elevation. Skin biopsy and clinical presentation were consistent with pustular psoriasis; nevertheless, the patient did not respond to high-potency topical corticosteroids and retinoid acid. As the patient presented with repeated skin flares early after birth, as well as serious constitutional distress with failure to thrive, an autoinflammatory syndrome like interleukine-1-receptor antagonist deficiency or interleukin-36-receptor antagonist deficiency (DITRA) was considered. The hypothesis was reinforced by parental consanguinity, and absence of skin lesion improvement under standard topical treatment. Genetic analyses showed a homozygous mutation in the IL36RN gene (L27P), which represents the same mutation recently described in DITRA patients. At age 6 months we started treatment with the recombinant interleukin-1 receptor antagonist anakinra with efficacy both on constitutional symptoms and skin involvement. DITRA is a recently described autoinflammatory disease characterized by repeated flares of generalized pustular psoriasis, high fever, asthenia, and systemic inflammation. We report herein the first exhaustive clinical description of an infant with DITRA who was successfully treated with anakinra.

AP1S3 Mutations Are Associated with Pustular Psoriasis and Impaired Toll-like Receptor 3 Trafficking

Adaptor protein complex 1 (AP-1) is an evolutionary conserved heterotetramer that promotes vesicular trafficking between the trans-Golgi network and the endosomes. The knockout of most murine AP-1 complex subunits is embryonically lethal, so the identification of human disease-associated alleles has the unique potential to deliver insights into gene function. Here, we report two founder mutations (c.11T>G [p.Phe4Cys] and c.97C>T [p.Arg33Trp]) in AP1S3, the gene encoding AP-1 complex subunit σ1C, in 15 unrelated individuals with a severe autoinflammatory skin disorder known as pustular psoriasis. Because the variants are predicted to destabilize the 3D structure of the AP-1 complex, we generated AP1S3-knockdown cell lines to investigate the consequences of AP-1 deficiency in skin keratinocytes. We found that AP1S3 silencing disrupted the endosomal translocation of the innate pattern-recognition receptor TLR-3 (Toll-like receptor 3) and resulted in a marked inhibition of downstream signaling. These findings identify pustular psoriasis as an autoinflammatory phenotype caused by defects in vesicular trafficking and demonstrate a requirement of AP-1 for Toll-like receptor homeostasis.