Role of tumour necrosis factor (TNF)-α and TNFRSF1A R92Q mutation in the pathogenesis of TNF receptor-associated periodic syndrome and multiple sclerosis

It has long been known that tumour necrosis factor (TNF)/TNFRSF1A signalling is involved in the pathophysiology of multiple sclerosis (MS). Different genetic and clinical findings over the last few years have generated renewed interest in this relationship. This paper provides an update on these recent findings. Genome-wide association studies have identified the R92Q mutation in the TNFRSF1A gene as a genetic risk factor for MS (odds ratio 1·6). This allele, which is also common in the general population and in other inflammatory conditions, therefore only implies a modest risk for MS and provides yet another piece of the puzzle that defines the multiple genetic risk factors for this disease. TNFRSF1A mutations have been associated with an autoinflammatory disease known as TNF receptor-associated periodic syndrome (TRAPS). Clinical observations have identified a group of MS patients carrying the R92Q mutation who have additional TRAPS symptoms. Hypothetically, the co-existence of MS and TRAPS or a co-morbidity relationship between the two could be mediated by this mutation. The TNFRSF1A R92Q mutation behaves as a genetic risk factor for MS and other inflammatory diseases, including TRAPS. Nevertheless, this mutation does not appear to be a severity marker of the disease, neither modifying the clinical progression of MS nor its therapeutic response. An alteration in TNF/TNFRS1A signalling may increase proinflammatory signals; the final clinical phenotype may possibly be determined by other genetic or environmental modifying factors that have not yet been identified.     

Identification of TNFRSF1B as a novel modifier gene in familial combined hyperlipidemia

Familial combined hyperlipidemia (FCHL) is the most commonly inherited hyperlipidemia in man, with a frequency of +/-1% in the general population and approximately 10% in myocardial infarction survivors. A genomic scan in 18 Dutch FCHL families resulted in the identification of several loci with evidence for linkage. One of these regions, 1p36.2, contains TNFRSF1B which encodes one of the tumor necrosis factor receptors. An intron 4 polymorphic CA-repeat was used to confirm linkage to FCHL. Linear regression analysis using 79 independent sib pairs showed linkage with a quantitative FCHL discriminant function (P = 0.032), and, borderline, with apolipoprotein B levels (P = 0.064). Furthermore, in a case-control study, association was demonstrated since the overall CA-repeat genotype distribution was significantly different among 40 unrelated FCHL patients and 48 unrelated healthy spouse controls (P = 0.029). This difference was due to a significant increase in allele CA271 homozygotes in the FCHL patients (P = 0.019). Mutation analysis of exon 6 in 73 FCHL family members demonstrated the presence of a single nucleotide polymorphism with two alleles, coding for methionine (196M) and arginine (196R). Complete linkage disequilibrium between CA267, CA271 and CA273 and this polymorphism was detected. In 85 hyperlipidemic FCHL subjects, an association was demonstrated between soluble TNFRSF1B plasma concentrations and the CA271-196M haplotype. In conclusion, TNFRSF1B was found to be associated with susceptibility to FCHL. Our data suggest that an as yet unknown disease-associated mutation, linked to alleles 196M and CA271, plays a role in the pathophysiology of FCHL.     

Allelic variants in genes associated with hereditary periodic fever syndromes as susceptibility factors for reactive systemic AA amyloidosis

We investigated the hypothesis that low-penetrance mutations in genes (TNFRSF1A, MEFV and NALP3/CIAS1) associated with hereditary periodic fever syndromes (HPFs) might be risk factors for AA amyloidosis among patients with chronic inflammatory disorders, including rheumatoid arthritis (RA), juvenile idiopathic arthritis (JIA), Crohn's disease, undiagnosed recurrent fevers and HPFs themselves. Four of 67 patients with RA plus amyloidosis had MEFV variants compared with none of 34 RA patients without amyloid (P value=0.03). The E148Q variant of MEFV was present in two of the three patients with TNF receptor-associated periodic syndrome (TRAPS) complicated by amyloid in two separate multiplex TRAPS families containing 5 and 16 affected members respectively, and the single patient with Muckle-Wells syndrome who had amyloidosis was homozygous for this variant. The R92Q variant of TNFRSF1A was present in two of 61 JIA patients with amyloidosis, and none of 31 nonamyloidotic JIA patients. No HPF gene mutations were found in 130 healthy control subjects. Although allelic variants in HPFs genes are not major susceptibility factors for AA amyloidosis in chronic inflammatory disease, low-penetrance variants of MEFV and TNFRSF1A may have clinically significant proinflammatory effects.     

Phenotypic variability in two patients with tumor necrosis factor receptor associated periodic fever syndrome emphasizes a rare manifestation: Immunoglobulin A nephropathy

Tumor necrosis factor receptor associated periodic fever syndrome (TRAPS) is caused by heterozygote mutations in TNFRSF1A, characterized by recurrent inflammatory attacks.In this report, we described two patients with different heterozygote mutations in TNFRSF1A. Patient 1, a 15-year-old male, had suffered from recurrent fever attacks accompanied by abdominal pain, eye manifestations, and myalgia with increased acute phase reactants since the age of 6-month. He had been unsuccessfully treated with colchicine for having familial Mediterranean fever without an identifiable MEFV mutation since the age of 4-year. At the age of 15 years, he was diagnosed with immunoglobulin (Ig) A nephropathy due to massive proteinuria and renal biopsy findings. Next generation sequencing revealed NM_001065.3: c.236C>T; p. (Thr79Met); T50M heterozygote mutation in TNFRFS1A. He was treated with methylprednisolone and cyclosporine for IgA nephropathy, thereafter with canakinumab for TRAPS. Patient 2, a 17-year-old female, had recurrent arthritis attacks accompanied by increased acute phase reactants for the last two months. She had neither fever attacks nor rashes or myalgia. Her physical examination was normal between attacks. Magnetic resonance imaging of both knees and ankles showed no signs of chronic arthritis. MEFV analyzes showed no mutation. Next generation sequencing revealed NM_001065.3: c.362G>A; p.(Arg121Gln); R92Q heterozygote mutation in TNFRFS1A. Arthritis attacks were treated successfully with ibuprofen thereafter.In conclusion, we wish to emphasize the diversity of the clinical manifestations between these two patients with distinct sequence variants in TNFRSF1A. Moreover, we presented a rare manifestation of TRAPS, IgA nephropathy.     

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

The hyperimmunoglobulinemia D and periodic fever syndrome (HIDS) is an autosomal recessively inherited autoinflammatory disease caused by mutations in the mevalonate kinase (MVK) gene on chromosome 12q24, which lead to a depressed enzymatic activity of mevalonate kinase (MK). TNF-receptor associated periodic syndrome (TRAPS), on the other hand, is the most frequent autosomal dominantly inherited periodic fever syndrome due to mutations in exons 2-4 and 6 of the TNFRSF1A gene on chromosome 12p13.2. We describe a girl with heterozygosity for the common MVK V377I mutation and for a novel T(1132) --> C transition, leading to the exchange of serine (TCC) by proline (CCC) at amino-acid position 378. Interestingly, our patient presented only with mild clinical features typical of HIDS and slightly increased immunoglobulin D levels, but a distinctly diminished MK activity. The girl was also heterozygous for the TNFRSF1A R92Q low-penetrance mutation, which may have significant proinflammatory effects. However, at the time of presentation, the patient had no TRAPS-associated symptoms.     

Unexpected high frequency of P46L TNFRSF1A allele in sub-Saharan West African populations

TNF receptor-associated periodic syndrome (TRAPS) is an autosomal dominant disorder characterized by recurrent attacks of fever and serositis. To date, more than 30 mutations have been reported in TNFRSF1A, the responsible gene. In Caucasian populations, the P46L (c.224C>T) TNFRSF1A sequence variation is considered as a low-penetrance mutation because its allele frequency is similar in patients and controls ( approximately 1%). Whereas the spectrum of TNFRSF1A gene mutations has been well established in Caucasian and several Mediterranean populations, it remains unknown in sub-Saharan African populations. In this study, we found an unexpected high P46L allele frequency ( approximately 10%) in two groups from West Africa - a group of 145 patients with sickle cell anaemia and a group of 349 healthy controls. These data suggest that the P46L variant is rather a polymorphism than a TRAPS causative mutation. We propose that the P46L high frequency in West African populations could be explained by some biological advantage conferred to carriers.     

Novel mutations in TNFRSF1A in patients with typical tumor necrosis factor receptor-associated periodic syndrome and with systemic lupus erythematosus in Japanese

Molecular defects of TNFRSF1A was investigated in members of a family presenting with typical phenotypes of tumor necrosis factor receptor-associated periodic syndrome (TRAPS) and in patients with the autoimmune disorders, systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Genomic DNA from the members of a family with typical TRAPS, as well as from 100 patients with SLE, 100 patients with RA and 100 healthy individuals, was studied for mutations in exons 2, 3 and 4 of the TNFRSF1A gene. All individuals were Japanese. Three novel missense mutations were identified in the TNFRSF1A. The C70G mutation was identified in family members with typical TRAPS, which was the second case in eastern Asian population. In addition, the T61I and R104Q mutations were each identified in 2 of the 100 SLE patients. The T61I mutation was identified in one of the 100 healthy individuals. No mutations were identified in the 100 RA patients. Functional analysis revealed that PMA-induced shedding of TNFRSF1A from PBMCs was impaired in a patient carrying T61I. A larger scale of study will clarify whether these two mutations, T61I and R104Q, are associated with chronic inflammatory disorders, such as SLE, or not.     

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.     

MEFV gene polymorphisms and TNFRSF1A mutation in patients with inflammatory myopathy with abundant macrophages

Inflammatory myopathy with abundant macrophages (IMAM) has recently been proposed as a new clinical condition. Although IMAM shares certain similarities with other inflammatory myopathies, the mechanisms responsible for this condition remain unknown. Patients with familial Mediterranean fever (FMF) and tumour necrosis factor receptor-associated periodic syndrome (TRAPS) also often develop myalgia. We therefore investigated the polymorphisms or mutations of MEFV and TNFRSF1A genes in patients with IMAM to identify their potential role in this condition. We analysed the clinical features of nine patients with IMAM and sequenced exons of the MEFV and TNFRSF1A genes. The patients with IMAM had clinical symptoms such as myalgia, muscle weakness, erythema, fever and arthralgia. Although none of the patients were diagnosed with FMF or TRAPS, seven demonstrated MEFV polymorphisms (G304R, R202R, E148Q, E148Q-L110P and P369S-R408Q), and one demonstrated a TNFRSF1A mutation (C43R). These results suggest that MEFV gene polymorphisms and TNFRSF1A mutation are susceptibility and modifier genes in IMAM.     

TNF and TNFR polymorphisms in severe sepsis and septic shock: a prospective multicentre study

Tumour necrosis factor (TNF) is an important pro-inflammatory cytokine produced in sepsis. Studies examining the association of individual TNF single nucleotide polymorphisms with sepsis have produced conflicting results. This study investigated whether common polymorphisms of the TNF locus and the two receptor genes, TNFRSF1A and TNFRSF1B, influence circulating levels of encoded proteins, and whether individual polymorphisms or extended haplotypes of these genes are associated with susceptibility, severity of illness or outcome in adult patients with severe sepsis or septic shock. A total of 213 Caucasian patients were recruited from eight intensive care units (ICU) in the UK and Australia. Plasma levels of TNF (P = 0.02), sTNFRSF1A (P = 0.005) and sTNFRSF1B (P = 0.01) were significantly higher in those who died on ICU compared to those who survived. There was a positive correlation between increasing soluble receptor levels and organ dysfunction (increasing SOFA score) (sTNFRSF1A R = 0.51, P < 0.001; sTNFRSF1B R = 0.53, P < 0.001), and in particular with the degree of renal dysfunction. In this study, there were no significant associations between the selected candidate TNF or TNF receptor polymorphisms, or their haplotypes, and susceptibility to sepsis, illness severity or outcome. The influence of polymorphisms of the TNF locus on susceptibility to, and outcome from sepsis remains uncertain.     

<Emphasis Type="Italic">TNFRSF13B/TACI</Emphasis> Alterations in Greek Patients with Antibody Deficiencies

TNFRSF13B/TACI defects have recently been associated with common variable immunodeficiency (CVID) pathogenesis. Considering that TNFRSF13B/TACI is very polymorphic and the frequency of its alterations may be different in various ethnic groups, we analyzed their prevalence in 47 Greek patients with antibody deficiencies, including CVID (16 patients), IgAD (16 patients), selective IgG4D (11 patients), and transient hypogammaglobulinemia of infancy (4 patients). A rather high frequency of TNFRSF13B/TACI defects was identified in patients with selective IgG4D (18.18%). Moreover, a patient with CVID was heterozygous in the common C104R mutation (6.25%). Both his children and a further healthy individual carried the same mutation, albeit without recurrent infections and/or hypogammaglobulinemia. The common polymorphisms V220A and P251L were identified in all disease subgroups, in an almost similar frequency with that observed in 259 healthy controls. Our data provide further evidence that TNFRSF13B/TACI alterations are not causative of CVID. Possibly, they predispose to humoral deficiencies and/or contribute to their phenotype when combined with other immune gene alterations.     

TNF receptor-associated periodic syndrome (TRAPS) in Japan: clinical characterization, pathogenesis, diagnostic criteria, and treatment]

TNF receptor-associated periodic syndrome (TRAPS) is an autosomal dominant inherited disease characterized by prolonged episodes of periodic fever and localized inflammation. The hypothetical pathogenesis of TRAPS is defective TNF receptor 1 (TNFRSF1A) shedding from cell membranes in response to a stimulus including TNFalpha. This mechanism has recently been shown to account for a minor population of TRAPS patients and other mechanisms are reported to explain the disease, such as resistance to apoptosis, TNFRSF1A internalization, or TNFRSF1A misfolding and aggregation, leading to NF-kappaB activation and apoptosis. Until now 15 TRAPS patients from 5 pedigree including 5 different mutations (C30R, C30Y, T61I, C70S, C70G) had been reported in Japan. There were many sporadic cases of TRAPS without TNFRSF1A mutation in our epidemiological study. In this issue, we described the clinical characterization, pathogenesis, diagnostic criteria, and treatment of TRAPS according to our case and literature.     

Sequence variants of the TNFRSF13B gene in Czech CVID and IgAD patients in the context of other populations

Mutations in the TNFRSF13B gene, encoding TACI, have been found in common variable immunodeficiency (CVID) and selective IgA deficient (IgAD) patients, but only the association with CVID seems to be significant. In this study, Czech CVID, IgAD and primary hypo/dysgammaglobulinemic (HG/DG) patients were screened for all TNFRSF13B sequence variants. The TNFRSF13B gene was mutated in 4/70 CVID patients (5.7%), 9/161 IgAD patients (5.6%), 1/17 HG/DG patient (5.9%) and none of 195 controls. Eight different mutations were detected, including the most frequent p.C104R and p.A181E mutations as well as 1 novel missense mutation, p.R189K. A significant association of TNFRSF13B gene mutations was observed in both CVID (p = 0.01) and IgAD (p = 0.002) Czech patients. However, when combined with all published data, only the association with CVID remained significant compared with the controls (9.9% vs. 3.2%, p < 10⁻⁶), while statistical significance disappeared for IgAD (5.7% vs. 3.2%, p = 0.145). The silent mutation p.P97P was shown to be associated significantly with CVID compared with the controls in both Czech patients (allele frequency 4.3% vs. 0.2%, p = 0.01) and in connection with the published data (5.1% vs. 1.8%, p = 0.003). The relevance of some TNFRSF13B gene variants remains unclear and needs to be elucidated in future studies.     

Novel Mutations in TACI (TNFRSF13B) Causing Common Variable Immunodeficiency

Introduction

Common variable immunodeficiency (CVID) is a heterogeneous syndrome characterized by impaired immunoglobulin production. The disorder is also characterized by co-occurrence of autoimmune, lymphoproliferative, and granulomatous diseases. Mutations in the gene encoding TACI (Transmembrane Activator and CAML Interactor, TNFRSF13B) were previously found to be associated with CVID.

Materials and Methods

We therefore sequenced TNFRSF13B gene in a cohort of 48 Iranian CVID patients. Expression of TACI and binding of A proliferation-inducing ligand (APRIL) were tested by FACS.

Results

We identified one patient with a homozygous G to T substitution in the TNFRSF13B gene at the splice site of intron 1 (c.61+1G>T), which abolished expression of the TACI molecule and binding capacity of APRIL. This represents the second CVID patient in the world with a complete absence of TACI expression. B cell lines from family members carrying the same mutation in a heterozygous form showed a reduced level of TACI expression and APRIL-binding capacity, suggesting a gene dosage effect. In addition, we found the previously recognized C104R and C172Y mutations in a heterozygous form in two patients with CVID and one, novel, heterozygous P42T mutation.

Conclusion

TACI mutations were observed in Iran CVID patients in a similar frequency as in other Caucasian populations. The novel mutations identified in this study support the notion of a crucial role for TACI in B cell differentiation.     

一个中国人裂手足伴并指趾畸形家系的表型和基因型分析

目的 确定一个中国人裂手足家系的致病性基因突变,探讨基因型-表型关系.方法 收集患者及其家庭成员的外周血,提取基因组DNA.采用PCR扩增P63基因和HOXD13基因的外显子,对PCR产物进行双向测序检测基因突变.结果 在所有患者中检测到P63基因第7外显子的杂合型956G→A突变,导致蛋白产物第280位的精氨酸被组氨酸取代(R280H).在正常家庭成员中未检测到该突变.结论 该家族中的患者以对称性裂手足伴并指趾为主要特征,由P63基因的R280H突变所致.     

Molecular Analysis of Myophosphorylase Deficiency in Dutch Patients with McArdle's Disease

We report on 8 Dutch patients with McArdle's disease from 6 unrelated families. Molecular analysis revealed the presence of four previously described mutations: the common R49X mutation, the IVS14+1G>A mutation and the recently reported R269X and Y84X nonsense mutations; and two new molecular defects: a missense mutation R138W in the homozygous state in two siblings, and a frameshift mutation c.1797delT. This first genetic study of patients from The Netherlands with McArdle's disease confirms that the R49X mutation is also the most common in Dutch patients, and that there is genetic heterogeneity within this population. Moreover, our data support the hypothesis that the Y84X mutation is a relatively frequent mutation in McArdle's patients with a Central European background, and expand the already crowded map of mutations within the PYGM gene responsible for McArdle's disease.     

Molecular genetic analysis of the gene encoding the trifunctional enzyme MTHFD (methylenetetrahydrofolate-dehydrogenase, methenyltetrahydrofolate-cyclohydrolase, formyltetrahydrofolate synthetase) in patients with neural tube defects

It is now well recognized that periconceptional folic acid or folic acid containing multivitamin supplementation reduces the risk of neural tube defects (NTDs). Recently we were able to show that homozygosity for a thermolabile variant of the enzyme methylenetetrahydrofolate reductase is associated with an increased risk for spina bifida in patients recruited from the Dutch population. However, this genetic risk factor could not account for all folic acid preventable NTDs. In an attempt to identify additional folate related enzymes that contribute to NTD etiology we now studied the methylenetetrahydrofolate dehydrogenase gene on chromosome 14q24 which encodes a single protein with three catalytic properties important in the folate metabolism. The cDNA sequence of 38 familial and 79 sporadic patients was screened for the presence of mutations by single strand conformation polymorphism (SSCP) analysis followed by sequencing. Two amino acid substitutions were identified. The first one (R293H) was detected in a patient with familial spina bifida and not in 300 control individuals. The mutation was inherited from the unaffected maternal grandmother and was also present in two younger brothers of the index patient, one of them displaying spina bifida occulta and the other being unaffected. The second change turned out to be an amino acid polymorphism (R653Q) that was present in both patients and controls with similar frequencies. Our results so far provide no evidence for a major role of the methylenetetrahydrofolate-dehydrogenase (MTHFD) gene in NTD etiology. However, the identification of a mutation in one family suggests that this gene can act as a risk factor for human NTD.     

Hyper IgD syndrome (HIDS) associated with in vitro evidence of defective monocyte TNFRSF1A shedding and partial response to TNF receptor blockade with etanercept

Hereditary periodic fever syndromes comprise a group of distinct disease entities linked by the defining feature of recurrent febrile episodes. Hyper IgD with periodic fever syndrome (HIDS) is caused by mutations in the mevalonate kinase (MVK) gene. The mechanisms by which defects in the MVK gene cause febrile episodes are unclear and there is no uniformly effective treatment. Mutations of the TNFRSF1A gene may also cause periodic fever syndrome (TRAPS). Treatment with the TNFR-Fc fusion protein, etanercept, is effective in some patients with TRAPS, but its clinical usefulness in HIDS has not been reported. We describe a 3-year-old boy in whom genetic screening revealed a rare combination of two MVK mutations producing clinical HIDS as well as a TNFRSF1A P46L variant present in about 1% of the population. In vitro functional assays demonstrated reduced receptor shedding in proband's monocytes. The proband therefore appears to have a novel clinical entity combining Hyper IgD syndrome with defective TNFRSF1A homeostasis, which is partially responsive to etanercept.     

Seven Novel Acid Sphingomyelinase Gene Mutations in Niemann-Pick Type A and B Patients

We have analyzed acid sphingomyelinase (SMPD1; E.C. 3.1.4.12) gene mutations in four Niemann‐Pick disease (NPD) type A and B patients of Turkish ancestry and in three patients of Dutch origin. Among four NPD type A patients we found two homozygotes for the g.1421C > T (H319Y) and g.3714T > C (Y537H) mutations and two compound heterozygotes, one for the g.3337T > C (F463S) and g.3373C > T (P475L) mutations and the other for the g.84delC (G29fsX74) and g.1208A > C (S248R) mutations. One of the type B patients was homozygous for the g.2629C>T (P371S) mutation. The last two type B patients were homozygotes for the common g.3927_3929delCGC (R608del) mutation. The G29fsX74, S248R, H319Y, P371S, F463S, P475L and Y537H SMPD1 mutations are all novel and were verified by PCR/RFLP and/or ARMS. All of the identified mutations are likely to be rare or private, with the exception of R608del which is prevalent among NPD type B patients from the North‐African Maghreb region. Geographical and/or social isolation of the affected families are likely contributing factors for the high number of homozygotes in our group.     

Determining the pathogenicity of patient-derived TSC2 mutations by functional characterization and clinical evidence

Tuberous sclerosis complex (TSC) is a genetic condition characterized by the growth of benign tumours in multiple organs, including the brain and kidneys, alongside intellectual disability and seizures. Identification of a causative mutation in TSC1 or TSC2 is important for accurate genetic counselling in affected families, but it is not always clear from genetic data whether a sequence variant is pathogenic or not. In vitro functional analysis could provide support for determining whether an unclassified TSC1 or TSC2 variant is disease-causing. We have performed a detailed functional analysis of four patient-derived TSC2 mutations, E92V, R505Q, H597R and L1624P. One mutant, E92V, functioned similarly to wild-type TSC2, whereas H597R and L1624P had abnormal function in all assays, consistent with available clinical and segregation information. One TSC2 mutation, R505Q, was identified in a patient with intellectual disability, seizures and autistic spectrum disorder but who did not fulfil the diagnostic criteria for TSC. The R505Q mutation was also found in two relatives, one with mild learning difficulties and one without apparent phenotypic abnormality. R505Q TSC2 exhibited partially disrupted function in our assays. These data highlight the difficulties of assessing pathogenicity of a mutation and suggest that multiple lines of evidence, both genetic and functional, are required to assess the pathogenicity of some mutations.