Identification of a novel mevalonate kinase gene mutation in combination with the common MVK V377I substitution and the low-penetrance TNFRSF1A R92Q mutation

Successful treatment with anakinra in generalized spiculated porokeratosis and severe hidradenitis suppurativa in a patient with MVK and MEFV mutations

The synergistic effect of two mutations of the innate immune system may facilitate hyperactivation and dysregulation of the inflammasome in skin macrophages. This case connects two diseases, hidradenitis suppurativa and porokeratosis, by the central role of autoinflammation.

Incomplete penetrance in primary immunodeficiency: a skeleton in the closet

Primary immunodeficiencies (PIDs) comprise a diverse group of over 400 genetic disorders that result in clinically apparent immune dysfunction. Although PIDs are classically considered as Mendelian disorders with complete penetrance, we now understand that absent or partial clinical disease is often noted in individuals harboring disease-causing genotypes. Despite the frequency of incomplete penetrance in PID, no conceptual framework exists to categorize and explain these occurrences. Here, by reviewing decades of reports on incomplete penetrance in PID we identify four recurrent themes of incomplete penetrance, namely genotype quality, (epi)genetic modification, environmental influence, and mosaicism. For each of these principles, we review what is known, underscore what remains unknown, and propose future experimental approaches to fill the gaps in our understanding. Although the content herein relates specifically to inborn errors of immunity, the concepts are generalizable across genetic diseases.

Where genotype is not predictive of phenotype: towards an understanding of the molecular basis of reduced penetrance in human inherited disease

Some individuals with a particular disease-causing mutation or genotype fail to express most if not all features of the disease in question, a phenomenon that is known as 'reduced (or incomplete) penetrance'. Reduced penetrance is not uncommon; indeed, there are many known examples of 'disease-causing mutations' that fail to cause disease in at least a proportion of the individuals who carry them. Reduced penetrance may therefore explain not only why genetic diseases are occasionally transmitted through unaffected parents, but also why healthy individuals can harbour quite large numbers of potentially disadvantageous variants in their genomes without suffering any obvious ill effects. Reduced penetrance can be a function of the specific mutation(s) involved or of allele dosage. It may also result from differential allelic expression, copy number variation or the modulating influence of additional genetic variants in cis or in trans. The penetrance of some pathogenic genotypes is known to be age- and/or sex-dependent. Variable penetrance may also reflect the action of unlinked modifier genes, epigenetic changes or environmental factors. At least in some cases, complete penetrance appears to require the presence of one or more genetic variants at other loci. In this review, we summarize the evidence for reduced penetrance being a widespread phenomenon in human genetics and explore some of the molecular mechanisms that may help to explain this enigmatic characteristic of human inherited disease.

Systemic AA amyloidosis as a unique manifestation of a combined mutation of TNFRSF1A and MEFV genes

We report the case of a 22-year-old Caucasian woman presenting with a new-onset nephrotic syndrome with normal renal function during the 35th week of pregnancy. AA (secondary) amyloidosis was further diagnosed at the renal biopsy. Extensive genetic testing revealed that the patient was heterozygous for both TNFRSF1A p.R92Q and MEFV p.M694I mutations leading to an autoinflammatory syndrome characterized by amyloid deposition as the sole manifestation.

A novel Y331X nonsense mutation in TNFRSF1A gene in two unrelated Turkish families with periodic fever syndrome

The autoinflammatory disorders differ in severity, as well as age of onset, duration, and manifestations, but they all share some common features: recurring fever peaks, inflammation of serosal membranes, musculoskeletal involvement, varying types of skin rash, amyloidosis as a sequel of the disease. TRAPS is very rare in Turkish population and we present two unrelated Turkish children with similar clinical phenotypes and laboratory findings related with autoinflammatory disorders and with novel p. Y331X mutation in TNFRSF1A gene. Both of the patients were male and they had recurrent fever without abdominal pain and arthralgia. Full cDNA and exon-intron binding regions of TNFRSF1A, MEFV, MVK, CIAS1 genes were analysed by direct DNA sequencing methods in order to differentiate TRAPS, FMF, HIDS, CINCA/MWS/FCAS respectively. We screened ten exons of TNFRSF1A gene, and detected a heterozygous c.1080C>G nucleotide substitution in exon 10 in both of the unrelated patients, resulting p.Y360X nonsense (protein truncated) mutation. According to classical TNFRSF1A gene nomenclature and the agreement of 30th amino acid as the first one, it is accepted as p.Y331X. It was interesting to determine same mutations in fathers of two patients. In one of the cases, E148Q heterozygous mutation, which is one of the disease-causing mutations of MEFV gene, was detected. No nucleotide substitution was identified in exon and exon-intron splicing regions encoding 396 amino acid of MVK gene in both of the patients. In CIAS1 gene, two different nucleotide substitutions resulting synonymous amino acid mutation were detected in exon 3: c.[732G>A] and c.[786A>G] nucleotide substitutions and compatible p.A242A (according to c.DNA p.A244A) and p.R260R (according to c.DNA p.R262R) synonymous amino acid mutations. These nucleotide substitutions were also detected in parents and were reported to be normal variations in Turkish population. In conclusion, in Turkish patients, with dominantly inherited recurrent fever, TRAPS is a diagnosis worthy of attention and novel mutations have to be reported with phenotype associations.

Incidence of TNFRSF1A mutations in German children: epidemiological, clinical and genetic characteristics

OBJECTIVE

TNF receptor 1-associated periodic syndrome (TRAPS) is a rare disease belonging to the heterogeneous group of hereditary periodic fever (HPF) syndromes. By their monogenic origins, the HPF syndromes are clearly differentiated from other periodic inflammatory episodes occurring in autoimmune, neoplastic and infectious diseases. We aim to determine the incidence of TRAPS and the spectrum of mutations in the TNFRSF1A gene, and to give a brief survey of clinical signs.

METHODS

A prospective surveillance of children with TRAPS was conducted in Germany during a time period of 3 years (2003-06). Monthly inquiries were sent to 370 children's hospitals by the German Pediatric Surveillance Unit (Clinic-ESPED, n1) and to 23 laboratories (Laboratory-ESPED, n2). Inclusion criteria were TNFRSF1A mutation-positive patients < or =16 years of age, more than three self-limiting episodes of fever >38.5 degrees C, and increased inflammation markers. Clinical, epidemiological and genetic data were evaluated via questionnaires.

RESULTS

Of the 23 cases included, 19 were identical in 20 clinical and 22 laboratory reports. The incidence of TRAPS in German children was estimated to be approximately 5.6 per 10(7) person-years. In 20 TRAPS patients of the Clinic-ESPED, median age of onset and duration of fever periods were 6 (range 1-16) years and 6.3 (range 2-24) days, respectively. Main symptoms were arthralgia, abdominal pain, lymphadenopathy, headache and skin involvement. The R92Q substitution was found in 19 (83%) of 23 cases.

CONCLUSION

The incidence of TRAPS is low and corresponds to 6-10 newly diagnosed patients < or =16 years per year in Germany.

Web resources for rare auto-inflammatory diseases: towards a common patient registry

OBJECTIVES

To review information resources on rare auto-inflammatory disorders (AIDs) for use by health care professionals, focusing particularly on patient registries.

METHODS

Using relevant key words, we surveyed the websites of several scientific societies of immunology, paediatrics and rheumatology, as well as Pubmed and specialized databases for AIDs.

RESULTS

The Internet provides a wide variety of information related to AIDs. Moreover, several other initiatives have been undertaken to create new resources for professionals. We reviewed six patient registries for rare AIDs, taking a special interest in the submission questionnaire. We revealed a wide overlap between the items used in the questionnaires, whereas the currently available registries appeared inappropriate for AIDs patients with complex or undefined diagnosis.

CONCLUSIONS

AIDs share common clinical features, pathophysiological pathways and therapeutic approaches. Although several resources are now available for rare AIDs, a unique and dedicated site gathering all aspects of these diseases as a whole is still lacking, i.e. covering research as well as the needs of AIDs patients and health care professionals. Our study thus advocates a merging of existing patient registries or the creation of a common database.

AA amyloidosis complicating hyperimmunoglobulinemia D with periodic fever syndrome: a report of two cases

AA amyloidosis is the most serious potential complication of the inherited autoinflammatory syndromes and frequently results in end-stage renal failure. Although this complication is well recognized in familial Mediterranean fever, tumor necrosis factor receptor-associated periodic syndrome, and Muckle-Wells syndrome, there is only 1 previous published report of its occurrence in hyperimmunoglobulinemia D with periodic fever syndrome (HIDS). We report 2 further cases of patients with AA amyloidosis in HIDS, both of whom developed dialysis-dependent renal failure, and we describe the outcome of the first renal transplant in this setting.

Mutational spectrum and genotype–phenotype correlations in mevalonate kinase deficiency

Mevalonate kinase deficiency (MKD) is an autosomal recessive autoinflammatory disorder caused by mutations in the MVK gene resulting in deficient activity of mevalonate kinase (MK). Depending on the clinical severity, MKD may present as hyper-IgD and periodic fever syndrome (HIDS) or the more severe mevalonic aciduria (MA). We analyzed the MVK gene in 57 patients with MKD and found 39 different mutations including 15 novel mutations, expanding the total mutational spectrum of MKD to 63 mutations. To get more insight into the genotype-phenotype correlation in MKD, we studied the effect of selected missense mutations on MK protein stability and activity in various patient fibroblast cell lines. All MKD cell lines showed markedly decreased MK activities that correlated well with the clinical severity and, for most of the cell lines, with the amount of MK protein. When fibroblasts of MKD patients were cultured under conditions known to promote a more controlled protein folding, all cell lines of patients with the HIDS phenotype and few cell lines of patients with the MA phenotype showed an increase in the residual MK activity. This increase in enzyme activity correlates well with an increase in the MK protein levels in these cell lines, indicating that most of the mutations in MKD affect stability and/or folding of the MK protein rather than affecting the catalytic properties of the enzyme. The finding that the residual activity in MKD can be manipulated by environmental conditions may offer therapeutic options to alleviate or prevent the clinical symptoms associated with MKD.

Neutrophils from patients withTNFRSF1A mutations display resistance to tumor necrosis factor–induced apoptosis: Pathogenetic and clinical implications

OBJECTIVE

To explore tumor necrosis factor (TNF)-induced apoptosis in neutrophils from patients with TNF receptor-associated periodic syndrome (TRAPS) and to correlate the results with the different kinds of TNFRSF1A mutations.

METHODS

Two hundred sixty-five patients with clinically suspected inherited autoinflammatory syndrome were screened for mutations of the TNFRSF1A gene. Neutrophils were isolated from heparinized blood by dextran sedimentation and incubated with and without cycloheximide (CHX) and TNFalpha. Cell apoptosis was assessed by human annexin V binding, and caspase 8 activation was assessed by flow cytometry.

RESULTS

Twenty-one patients were found to carry a variant of the TNFRSF1A gene: 13 patients had an R92Q substitution, and 8 patients presented other missense substitutions, 1 splicing mutation, and 1 in-frame interstitial deletion. Neutrophil stimulation with TNF and CHX was associated with induction of apoptosis in 12 normal controls and in 10 subjects with the R92Q mutation. Conversely, neutrophils from 8 TRAPS patients with mutations of cysteine or threonine residues or interstitial deletion did not show any induction of apoptosis after stimulation. The incidence of the R92Q mutation among patients with recurrent autoinflammatory syndromes was similar to that observed in the normal population.

CONCLUSION

Resistance to TNF-mediated apoptosis is a feature in TRAPS patients who have mutations of cysteine residues or interstitial deletion, and may play a pathogenic role. The R92Q mutation does not appear to be significantly associated with TRAPS.

Approach to genetic analysis in the diagnosis of hereditary autoinflammatory syndromes

OBJECTIVE

Hereditary autoinflammatory syndromes are characterized by recurrent episodes of fever and inflammation. Seven subtypes have been described, caused by mutations in four different genes. Apart from a common phenotype of lifelong recurrent inflammatory attacks, all subtypes have distinct features and specific therapeutic options, which emphasizes the need for a specific diagnosis in each case. Our aim was to examine whether genetic screening would allow classification of previously unclassified patients, and whether individual patients suffering from an autoinflammatory syndrome carry additional mutations in one of the other autoinflammatory genes.

METHODS

We included 60 patients with an unclassified autoinflammatory syndrome, 87 patients diagnosed with either hyper-IgD syndrome, familial Mediterranean fever (FMF) or tumour necrosis factor (TNF)-receptor-associated periodic syndrome and 50 healthy controls. Deoxyribonucleic acid samples were screened for the most prevalent mutations in the MEFV, TNFRSF1A, MVK and CIAS1 genes.

RESULTS

We found only one possible diagnosis of FMF in the 60 previously unclassified patients. Two low-penetrance mutations were found in equal numbers in the groups of patients and controls.

CONCLUSIONS

Screening of highly prevalent mutations in known genes involved in these disorders does not yield additional relevant information. Differential diagnosis of hereditary autoinflammatory syndromes can be made by thorough clinical examination followed by targeted genetic analysis of the one or two most likely syndromes. High-prevalence low-penetrant mutations from autoinflammatory genes do not occur more frequently in patients with hereditary autoinflammatory syndromes compared with the general population.

Familial autoinflammatory diseases: genetics, pathogenesis and treatment

PURPOSE OF REVIEW

The systemic autoinflammatory diseases are characterized by seemingly unprovoked inflammation, without major involvement of the adaptive immune system. This review focuses mainly on a subset of these illnesses, the hereditary recurrent fevers, which include familial Mediterranean fever, the tumor necrosis factor receptor-associated periodic syndrome, the hyperimmunoglobulinemia D with periodic fever syndrome, and cryopyrin-associated periodic syndromes. This review elucidates how recent advances have impacted diagnosis, pathogenesis, and treatment.

RECENT FINDINGS

More than 170 mutations have been identified in the four genes underlying the six hereditary recurrent fevers. Genetic testing has broadened the clinical and geographic boundaries of these illnesses, given rise to the concept of the cryopyrin-associated periodic syndromes as a disease spectrum, and permitted diagnosis of compound heterozygotes for mutations in two different hereditary recurrent fever genes. Genetics has also advanced our understanding of amyloidosis, a complication of the hereditary recurrent fevers, and suggested a possible role for common hereditary recurrent fever variants in other inflammatory conditions. Recent advances in molecular pathophysiology include the elucidation of the N-terminal PYRIN domain in protein-protein interactions, the description of the NALP3 (cryopyrin) inflammasome as a macromolecular complex for interleukin-1beta activation, and the identification of signaling defects other than defective receptor shedding in patients with tumor necrosis factor receptor-associated periodic syndrome. These molecular insights form the conceptual basis for targeted biologic therapies.

SUMMARY

Advances in molecular genetics extend our ability to recognize and treat patients with systemic autoinflammatory diseases and inform our understanding of the regulation of innate immunity in humans.