Asymptomatic Family Members Research Articles

Novel X-linked glomerulopathy is associated with a COL4A5 missense mutation in a non-collagenous interruption

A novel COL4A5 mutation causes rapid progression to end-stage renal disease in males, despite the absence of clinical and biopsy findings associated with Alport syndrome. Affected males have proteinuria, variable hematuria, and an early progression to end-stage renal disease. Renal biopsy findings include global and segmental glomerulosclerosis, mesangial hypercellularity and basement membrane immune complex deposition. Exon sequencing of the COL4A5 locus identified a thymine to guanine transversion at nucleotide 665, resulting in a phenylalanine to cysteine missense mutation at codon 222. The phenylalanine at position 222 is absolutely conserved among vertebrates. This mutation was confirmed in 4 affected males and 4 female obligate carriers, but was absent in 6 asymptomatic male family members and 198 unrelated individuals. Immunostaining for α5(IV) collagen in renal biopsies from affected males was normal. This mutation, in a non-collagenous interruption associated with severe renal disease, provides evidence for the importance of this structural motif and suggests the range of phenotypes associated with COL4A5 mutations is more diverse than previously realized. Hence, COL4A5 mutation analysis should be considered when glomerulonephritis presents in an X-linked inheritance pattern, even with a presentation distinct from Alport syndrome.

Young Investigator Award Session * Friday 10 December 2010, 12:45-13:45

Young Investigator Award Session * Friday 10 December 2010, 12:45-13:45

Clinical & Molecular Analysis of Patients with Type 2 (Qualitative) Hereditary Antithrombin (AT) Deficiency

AbstractAbstract 4201 Background:Hereditary AT deficiency is classified as type 1 (quantitative) or type 2 (qualitative). Type 2 deficiency can be further subdivided into type 2a (reactive center loop [RCL]), type 2b (heparin binding domain), and type 2c (pleiotropic) based on functional and molecular AT analysis. Patients with heterozygous type 2b AT deficiency are thought to be at a lower risk for venous thromboembolism (VTE). Objectives:1) To estimate the frequency of type 2 hereditary AT deficiency. 2) To utilize molecular analysis to accurately sub type patients with type 2 defects. 3) To correlate thrombotic and obstetric complications with AT deficiency sub types. Methods:Apparently unrelated Mayo Clinic AT-deficient patients (n=20) were categorized as type 1 or 2 based on plasma AT activity and antigen, or by molecular analysis for previously reported type 2a-c mutations. Demographic and clinical characteristics were abstracted from patient medical records. The SERPINC1 putative promoter region, all exons (n=7) and splice junctions, and the 3′UTR were PCR amplified from leukocyte genomic DNA, and sequenced with nested forward and reverse primers. For patients without identifiable mutations, multiplex ligand-dependent probe amplification (MLPA) was performed. Results:Out of 20 probands tested 7 (35%) had type 2 AT deficiency. The mean patient age at diagnosis was 36 years (range 18–65) and 5 (69%) were women. There were 2 patients with type 2a, 4 with type 2b (including 1 with a homozygous defect), and 1 with type 2c AT deficiency. The mean plasma AT (range) activity/antigen for these patients were 50% (37-67%)/93% (78-103%) [AT activity & antigen normal range=80-130%]. 6 patients had a previously described mutation, whereas 1 had a novel mutation [S380R] affecting the RCL (Table1). All patients with type 2a and type 2c AT deficiency had unprovoked VTE occurring at a young age. All 3 patients with heterozygous type 2b AT deficiency had no VTE or obstetric complications. One patient with a homozygous type 2b defect (AT Vienna) presented with an unprovoked DVT at age 15. One family with AT Toyama (type 2b AT deficiency) had 5 asymptomatic adult family members with the mutation. Background:Molecular testing is important for an accurate subtyping of patients with type 2 AT deficiency. Type 2 defects have a diverse clinical spectrum. Patients with heterozygous type 2b AT deficiency have a low rate of VTE and obstetric complications. Homozygous type 2b AT deficiency can be compatible with adult life. Disclosures:No relevant conflicts of interest to declare.

Clinical guidelines for testing for heritable thrombophilia

Trevor Baglin, Elaine Gray, Mike Greaves, Beverley J. Hunt, David Keeling, Sam Machin, Ian Mackie, Mike Makris, Tim Nokes, David Perry, R. C. Tait, Isobel Walker and Henry Watson Addenbrooke’s Hospital, Cambridge, NIBSC, South Mimms, University of Aberdeen, Aberdeen, Guy’s and St Thomas’, London, Churchill Hospital, Oxford, University College Hospital, London, Royal Hallamshire Hospital, Sheffield, Derriford Hospital, Plymouth, Glasgow Royal Infirmary, Glasgow and Aberdeen Royal Infirmary, UK

Study of the BMPR2 Gene in Patients with Pulmonary Arterial Hypertension

IntroductionMutations of the gene that code bone morphogenic protein type 2 receptor (BMPR2) are involved in the pathogenesis of pulmonary arterial hypertension (PAH), both in its familial (FPAH) and its idiopathic (IPAH) forms. MethodWith the aim of increasing the knowledge of these genetic factors in our area, the BMPR2 gene was studied in 17 patients with PAH, 8 with FPAH and 9 with sporadic IPAH. Additionally, a study was made to see whether the presence of BMPR2 mutations was associated with changes in the CO diffusing CO (DLCO) with the aim of evaluating the interest in this measurement in the pre-clinical diagnosis. ResultsR491Q y R211X mutations were detected in 2 patients with FPAH (prevalence, 25%), and the R332X mutation in one case of IPAH (prevalence, 11%). The familial study of the patient with the R491Q mutation, 14 of the 28 subjects studied had the mutation, and 4 had the diseases (penetration, 36%). A decrease in the DLCO/alveolar volume (KCO) ratio was observed in asymptomatic family members who expressed the mutation, compared to those who did not express it (88±5% and 104±9% of the reference value, respectively; P<.01). ConclusionWe conclude that the frequency of mutations in the BMPR2 gene in the patients studied with FPAH is lower than was previously described. The decrease in the KCO observed in asymptomatic carriers of the mutation suggests a certain level of pulmonary vascular changes, therefore its measurement could be useful in the familial study of FPAH.

The role of cardiac magnetic resonance imaging in differentiating the underlying causes of left ventricular hypertrophy

The onset of sudden cardiac death and large inter- and intra-familial clinical variability of hypertrophic cardiomyopathy pose an important clinical challenge. Cardiac magnetic resonance imaging is a high-resolution imaging modality that has become increasingly available in the past decade and has the unique possibility to demonstrate the presence of fibrosis or scar using late gadolinium enhancement imaging. As a result, the diagnostic and prognostic potential of cardiac magnetic resonance imaging has been extensively explored in acute and chronic ischaemic cardiomyopathy, as well as in several nonischaemic cardiomyopathies.This review aims to provide a critical overview of recently published studies on hypertrophic cardiomyopathy and discusses the role of cardiac magnetic resonance imaging in differentiating underlying causes of hypertrophic cardiomyopathy, such as familial hypertrophic cardiomyopathy, cardiac involvement in systemic disease and left ventricular hypertrophy due to endurance sports. Also, it demonstrates the use of cardiac magnetic resonance in risk stratification for the onset of sudden cardiac death, and early identification of asymptomatic family members of hypertrophic cardiomyopathy patients who are at risk for the development of hypertrophic cardiomyopathy. (Neth Heart J 2010;18:135-43.).

Novel non‐sense GCH1 mutation in a South African family diagnosed with dopa‐responsive dystonia

Dopa-responsive dystonia (DRD), a movement disorder characterized by onset in early childhood and a dramatic response to low doses of levodopa, has been shown to be caused by a number of different mutations in the GCH1 gene. We identified a South African family which presented with DRD in three family members. Polymerase chain reaction (PCR) primers were designed to span all six exons of GCH1 and the PCR products were screened for pathogenic mutations using direct sequencing. A novel non-sense mutation (c.233delT; p.I78fsX79) was identified in the DRD patients, which would produce a markedly truncated protein of only 78 amino acids. This mutation was also present in a number of asymptomatic family members. A novel non-sense mutation in the GCH1 gene can be associated with DRD and reduced penetrance in South African patients.

Estudio del gen BMPR2 en pacientes con hipertensión arterial pulmonar

Introduction Mutations of the gene that code bone morphogenic protein type 2 receptor (BMPR2) are involved in the pathogenesis of pulmonary arterial hypertension (PAH), both in its familial (FPAH) and its idiopathic (IPAH) forms. Method With the aim of increasing the knowledge of these genetic factors in our area, the BMPR2 gene was studied in 17 patients with PAH, 8 with FPAH and 9 with sporadic IPAH. Additionally, a study was made to see whether the presence of BMPR2 mutations was associated with changes in the CO diffusing CO (DL CO) with the aim of evaluating the interest in this measurement in the pre-clinical diagnosis. Results R491Q y R211X mutations were detected in 2 patients with FPAH (prevalence, 25%), and the R332X mutation in one case of IPAH (prevalence, 11%). The familial study of the patient with the R491Q mutation, 14 of the 28 subjects studied had the mutation, and 4 had the diseases (penetration, 36%). A decrease in the DL CO/alveolar volume (K CO) ratio was observed in asymptomatic family members who expressed the mutation, compared to those who did not express it (88±5% and 104±9% of the reference value, respectively; P<0.01). Conclusion We conclude that the frequency of mutations in the BMPR2 gene in the patients studied with FPAH is lower than was previously described. The decrease in the K CO observed in asymptomatic carriers of the mutation suggests a certain level of pulmonary vascular changes, therefore its measurement could be useful in the familial study of FPAH.

Presence and significance of a R110W mutation in the DNA-binding domain of GCM2 gene in patients with isolated hypoparathyroidism and their family members

Glial cells missing 2 (GCM2) gene encodes a parathyroid-specific transcription factor. We assessed GCM2 gene sequence in patients with isolated hypoparathyroidism (IH). Case-control study. Complete DNA sequencing of the GCM2 gene including its exons, promoter, and 5' and 3' UTRs was performed in 24/101 patients with IH. PCR-restriction fragment length polymorphism was used to detect a novel R110W mutation in all 101 IH patients and 655 healthy controls. Significance of the mutation was assessed by electrophoretic mobility shift assay (EMSA) and nuclear localization on transfection. A heterozygous R110W mutation was present in DNA-binding domain in 11/101 patients (10.9%) and absent in 655 controls (P<10(-7)). Four of 13 nonaffected first-degree relatives for five of these index cases had R110W mutation. Four heterozygous single nucleotide polymorphisms were found in the 5' region. One of the 11 patients with R110W also had T370M change in compound heterozygous form. Mutant R110W and T370M GCM2 proteins showed decreased binding with GCM recognition elements on EMSA indicating loss of function. Both wild-type and R110W mutant GCM2 proteins showed nuclear localization. The present study indicates a significant association of R110W variant with IH. Absence of effect of heterozygous R110W mutation on DNA binding and presence of the same mutation in asymptomatic family members indicate that additional genetic (akin to T370M change) or nongenetic factors might contribute to the expression of diseases in IH. Alternatively, it is possible that association of R110W with IH could be due to linkage disequilibrium with the unidentified relevant genes in IH.

Clinical features and functional significance of the P369S/R408Q variant in pyrin, the familial Mediterranean fever protein

ObjectivesFamilial Mediterranean fever (FMF) is caused by mutations in MEFV, which encodes pyrin. The nature of substitutions P369S and R408Q in exon 3 remains unclear. Exon 3 encoding pyrin's B-box...

Metabolomic Profiling in LRRK2-Related Parkinson's Disease

BackgroundMutations in LRRK2 gene represent the most common known genetic cause of Parkinson's disease (PD).Methodology/Principal FindingsWe used metabolomic profiling to identify biomarkers that are associated with idiopathic and LRRK2 PD. We compared plasma metabolomic profiles of patients with PD due to the G2019S LRRK2 mutation, to asymptomatic family members of these patients either with or without G2019S LRRK2 mutations, and to patients with idiopathic PD, as well as non-related control subjects. We found that metabolomic profiles of both idiopathic PD and LRRK2 PD subjects were clearly separated from controls. LRRK2 PD patients had metabolomic profiles distinguishable from those with idiopathic PD, and the profiles could predict whether the PD was secondary to LRRK2 mutations or idiopathic. Metabolomic profiles of LRRK2 PD patients were well separated from their family members, but there was a slight overlap between family members with and without LRRK2 mutations. Both LRRK2 and idiopathic PD patients showed significantly reduced uric acid levels. We also found a significant decrease in levels of hypoxanthine and in the ratios of major metabolites of the purine pathway in plasma of PD patients.Conclusions/SignificanceThese findings show that LRRK2 patients with the G2019S mutation have unique metabolomic profiles that distinguish them from patients with idiopathic PD. Furthermore, asymptomatic LRRK2 carriers can be separated from gene negative family members, which raises the possibility that metabolomic profiles could be useful in predicting which LRRK2 carriers will eventually develop PD. The results also suggest that there are aberrations in the purine pathway in PD which may occur upstream from uric acid.

Familial Asymptomatic Macular Telangiectasia Type 2

To report findings in asymptomatic family members of patients with macular telangiectasia type 2. Prospective, observational, cross-sectional case series. Four patients with symptomatic macular telangiectasia type 2 (index patients) and 5 relatives, including 2 sets of monozygotic twins. Screening of family members of participants in a non-interventional natural history study of macular telangiectasia type 2. Ophthalmologic examination included best-corrected visual acuity testing, fundus biomicroscopy, fluorescein angiography (FA), optical coherence tomography (OCT), and fundus autofluorescence (FAF) imaging. Evidence for macular telangiectasia type 2 in any of the imaging methods used and visual function of the family members studied. In the first family, 2 of 3 daughters of a severely affected 68-year-old woman had features of macular telangiectasia type 2. Although one of the daughters was diagnosed by biomicroscopic examination, the second daughter was diagnosed only by subtle changes on OCT and FAF imaging. Both affected daughters were asymptomatic and were unaware that they had the condition. In the second family, clinical examination showed that the 60-year-old brother of the 75-year-old index patient obviously was affected, despite a lack of any subjective visual dysfunction. The 65-year-old monozygotic twin of the third index patient showed a slight retinal thinning within a small area temporal to the foveola in both eyes as well as minor staining on FA and a subtle monocular loss of macular pigment. The 56-year-old asymptomatic monozygotic twin of the last proband had opacification of the retina with leakage on FA in the right eye. The fellow eye was unremarkable except for an abnormal FAF signal that was present in both eyes. Macular telangiectasia type 2 may be more common than previously assumed, but patients may not seek ophthalmic care if their visual function is normal. The study of these early, asymptomatic cases may yield valuable insights into the pathogenesis of the condition. Further research is warranted to determine whether there is an underlying, dominantly inherited genetic abnormality in macular telangiectasia type 2 of variable penetrance and expressivity.

Outcomes of nasopharyngeal carcinoma screening for high risk family members in Hong Kong

We undertook a large retrospective study to evaluate the impact of screening family members of NPC patients with Epstein Barr Virus (EBV) serology. 1,199 asymptomatic family members of NPC patients were entered into the annual screening program with EBV serology and nasopharyngoscopy between 1994 and 2005. Eighteen participants of our screening program developed NPC; 17 of them were treated in our institute, of whom 16 were detected in screening. The sensitivity and specificity of EBV serology were 83.3 and 87.0%, respectively, and for the program they were 88.9 and 87.0%, respectively. Stage distributions and survival outcomes of the 17 cases were compared with that of 1,185 consecutive symptomatic patients diagnosed in the same period through general referral. It was found that the screening program resulted in early detection of cancer, with 59% presenting at early stage (stage I: 41%, stage II: 18%) compared to 24% (stage I: < 1%, stage II: 23%) of symptomatic cancers (P < 0.001), and a significant improvement in disease-free survival (P = 0.04). The cancer specific survival and overall survival rate at 5-year are also higher (92 vs. 77% and 92 vs. 70%, respectively), though they fail to reach statistical significance. In conclusion, screening asymptomatic family members of NPC patients annually leads to earlier detection of NPC and clinically valuable survival advantage among these family members. A larger sample size is needed to confirm its full potential in survival benefit.

Structural myocardial abnormalities in asymptomatic family members with Brugada syndrome and SCN5A gene mutation

It is still debated whether Channellopathies should be considered as genetically mediated functional electrical disorders or rather cardiomyopathies with prominent electrical instability. An indication towards the second option has been recently provided, reporting …

Thrombophilia: 2009 update

As venous thrombosis is mostly caused by disturbances in the plasma coagulation system, abnormalities of coagulation factors are mostly risk factors for venous thromboembolism (VTE). Relatively little is known about thrombophilias that predispose to arterial thromboembolism. Although some abnormalities in the fibrinolytic pathway appear to predispose to arterial thrombosis, the associations are weak and often inconsistent between studies. At present, there is not enough consistent and clinically meaningful information to include fibrinolytic parameters in a clinical thrombophilia workup. Controversy exists as to which patients and family members to test for thrombophilia. Several testing guidelines exist. Routine screening for inherited thrombophilias is not indicated in patients with VTE provoked by immobility, surgery, and malignancy, or in those with arterial thrombosis with arteriosclerosis risk factors. Heterozygous factor V Leiden (FVL) and prothrombin 20210 mutations increase the risk for recurrent VTE only slightly once anticoagulation is stopped. Therefore, decisions regarding the length of anticoagulant therapy typically are not influenced by finding one of these heterozygous mutations. The main reason to perform thrombophilia testing in a patient is to detect a strong thrombophilia (ie, antithrombin deficiency, antiphospholipid antibody syndrome, homozygous FVL, double-heterozygous FVL plus prothrombin 20210 mutation, protein C deficiency, and maybe protein S deficiency). The finding of a strong thrombophilia has several clinical consequences: it decreases the threshold to recommend long-term anticoagulation in a patient with unprovoked VTE; facilitates discussion regarding whether anticoagulant or antiplatelet therapy is the preferred empiric treatment for a patient who had an unexplained arterial, nonarteriosclerotic thromboembolic event; and leads to the consideration of testing asymptomatic female family members for the identified thrombophilia(s) so they can be counseled on their risk of thromboembolism, the use of hormonal therapies, and the potential benefit of pre- and postpartum anticoagulant therapy.

Greater Rupture Risk for Familial as Compared to Sporadic Unruptured Intracranial Aneurysms

The risk of intracranial aneurysm (IA) rupture in asymptomatic members of families who have multiple affected individuals is not known. First-degree unaffected relatives of those with a familial history of IA who had a history of smoking or hypertension but no known IA were offered cerebral MR angiography (MRA) and followed yearly as part of a National Institute of Neurological Diseases and Stroke-funded study of familial IA (Familial Intracranial Aneurysm [FIA] Study). A total of 2874 subjects from 542 FIA Study families were enrolled. After study enrollment, MRAs were performed in 548 FIA Study family members with no known history of IA. Of these 548 subjects, 113 subjects (20.6%) had 148 IAs by MRA of whom 5 subjects had IA >or=7 mm. Two subjects with an unruptured IA by MRA/CT angiography (3-mm and 4-mm anterior communicating artery) subsequently had rupture of their IA. This represents an annual rate of 1.2 ruptures per 100 subjects (1.2% per year; 95% CI, 0.14% to 4.3% per year). None of the 435 subjects with a negative MRA have had a ruptured IA. Survival curves between the MRA-positive and -negative cohorts were significantly different (P=0.004). This rupture rate of unruptured IA in the FIA Study cohort of 1.2% per year is approximately 17 times higher than the rupture rate for subjects with an unruptured IA in the International Study of Unruptured Aneurysm Study with a matched distribution of IA size and location 0.069% per year. Small unruptured IAs in patients from FIA Study families may have a higher risk of rupture than sporadic unruptured IAs of similar size, which should be considered in the management of these patients.

Plasma progranulin levels predict progranulin mutation status in frontotemporal dementia patients and asymptomatic family members

Mutations in the progranulin gene (GRN) are an important cause of frontotemporal lobar degeneration (FTLD) with ubiquitin and TAR DNA-binding protein 43 (TDP43)-positive pathology. The clinical presentation associated with GRN mutations is heterogeneous and may include clinical probable Alzheimer's disease. All GRN mutations identified thus far cause disease through a uniform disease mechanism, i.e. the loss of functional GRN or haploinsufficiency. To determine if expression of GRN in plasma could predict GRN mutation status and could be used as a biological marker, we optimized a GRN ELISA and studied plasma samples of a consecutive clinical FTLD series of 219 patients, 70 control individuals, 72 early-onset probable Alzheimer's disease patients and nine symptomatic and 18 asymptomatic relatives of GRN mutation families. All FTLD patients with GRN loss-of-function mutations showed significantly reduced levels of GRN in plasma to about one third of the levels observed in non-GRN carriers and control individuals (P < 0.001). No overlap in distributions of GRN levels was observed between the eight GRN loss-of-function mutation carriers (range: 53–94 ng/ml) and 191 non-GRN mutation carriers (range: 115–386 ng/ml). Similar low levels of GRN were identified in asymptomatic GRN mutation carriers. Importantly, ELISA analyses also identified one probable Alzheimer's disease patient (1.4%) carrying a loss-of-function mutation in GRN. Biochemical analyses further showed that the GRN ELISA only detects full-length GRN, no intermediate granulin fragments. This study demonstrates that using a GRN ELISA in plasma, pathogenic GRN mutations can be accurately detected in symptomatic and asymptomatic carriers. The ∼75% reduction in full-length GRN, suggests an unbalanced GRN metabolism in loss-of-function mutation carriers whereby more GRN is processed into granulins. We propose that plasma GRN levels could be used as a reliable and inexpensive tool to identify all GRN mutation carriers in early-onset dementia populations and asymptomatic at-risk individuals.

TERC and TERT gene mutations in patients with bone marrow failure and the significance of telomere length measurements

AbstractDyskeratosis congenita (DC) is a rare inherited form of bone marrow failure (BMF) caused by mutations in telomere maintaining genes including TERC and TERT. Here we studied the prevalence of TERC and TERT gene mutations and of telomere shortening in an unselected population of patients with BMF at our medical center and in a selected group of patients referred from outside institutions. Less than 5% of patients with BMF had pathogenic mutations in TERC or TERT. In patients with BMF, pathogenic TERC or TERT gene mutations were invariably associated with marked telomere shortening (≪ 1st percentile) in peripheral blood mononuclear cells (PBMCs). In asymptomatic family members, however, telomere length was not a reliable predictor for the presence or absence of a TERC or TERT gene mutation. Telomere shortening was not pathognomonic of DC, as approximately 30% of patients with BMF due to other causes had PBMC telomere lengths at the 1st percentile or lower. We conclude that in the setting of BMF, measurement of telomere length is a sensitive but nonspecific screening method for DC. In the absence of BMF, telomere length measurements should be interpreted with caution.

Tumor necrosis factor receptor–associated periodic syndrome: Toward a molecular understanding of the systemic autoinflammatory diseases

Almost a decade has elapsed since the concept of autoinflammation was advanced to describe conditions characterized by ostensibly unprovoked inflammation, without the hightiter autoantibodies or antigen-specific T-cells found in known autoimmune diseases. This concept was introduced following the identification of mutations in the p55 tumor necrosis factor receptor (TNFR1) in patients with a dominantly inherited syndrome of systemic inflammation (TRAPS) (1). Systemic autoinflammatory diseases are caused by aberrant activation of the innate immune system. Some result in recurrent episodes of fever, localized serositis and skin rashes. Two hereditary recurrent fevers, familial Mediterranean fever (FMF) and the TNF receptor-associated periodic syndrome (TRAPS) were prototypes for this diagnostic category. In the past 10 years this concept has been extended to include a number of Mendelian disorders, including other hereditary recurrent fevers, as well as more common diseases with complex modes of inheritance including Behcet's disease and Crohn's disease (2). When the molecular basis of TRAPS was discovered it was considered an exceedingly rare disease with only a few families described in the literature. Over the past decade, more than 50 disease-associated mutations have been identified in hundreds of patients from a variety of ethnic backgrounds (3). Genotype-phenotype studies showed that mutations at cysteine residues are associated with a more severe phenotype and higher incidence of amyloidosis (4). Although, most TRAPS-associated mutations are fully penetrant, two TNFR1 variants, P46L and R92Q, have been also identified in asymptomatic family members, and at a low frequency in healthy populations. Tumor necrosis factor (TNF) is a pleiotropic cytokine that mediates a wide range of cellular activities primarily through its interaction with TNF receptor 1 (TNFR1; TNFRSF1A; CD120a; p55/p60). Triggering the TNF signaling cascade results in an array of responses, including apoptosis, inflammation and modulation of the immune response. TNFR1 is constitutively expressed on the cell surface in most tissues. It is a large polypeptide with an extracellular domain, consisting of 4 cysteine-rich domains (CRD), a transmembrane domain, and an intracellular death domain (DD). Each CRD includes 3 pairs of cysteine residues that form intramolecular disulfide bonds important in maintaining the 3dimensional conformation of the extracellular part of the receptor. Thus, a substitution at a cysteine residue has the potential to disrupt the relevant disulfide bond and result in significant structural perturbation. The first CRD, sometimes called the pre-ligand association domain (PLAD), allows for TNF-independent interactions of TNFR1 molecules,

Breakpoint characterization of a novel ∼59 kb genomic deletion on 19q13.42 in autosomal-dominant retinitis pigmentosa with incomplete penetrance

The aim of this study was to identify and characterize the underlying molecular mechanisms in autosomal-dominant retinitis pigmentosa (adRP) with incomplete penetrance in two Swedish families. An extended genealogical study and haplotype analysis indicated a common origin. Mutation identification was carried out by multiplex ligation-dependent probe amplification (MLPA) and sequencing. Clinical examinations of adRP families including electroretinography revealed obligate gene carriers without abnormalities, which indicated incomplete penetrance. Linkage analysis resulted in mapping of the disease locus to 19q13.42 (RP11). Sequence analyses did not reveal any mutations segregating with the disease in eight genes including PRPF31. Subsequent MLPA detected a large genomic deletion of 11 exons in the PRPF31 gene and, additionally, three genes upstream of the PRPF31. Breakpoints occurred in intron 11 of PRPF31 and in LOC441864, 'similar to osteoclast-associated receptor isoform 5.' An almost 59 kb deletion segregated with the disease in all affected individuals and was present in several asymptomatic family members but not in 20 simplex RP cases or 94 healthy controls tested by allele-specific PCR. A large genomic deletion resulting in almost entire loss of PRPF31 and three additional genes identified as the cause of adRP in two Swedish families provide an additional evidence that mechanism of the disease evolvement is haploinsufficiency. Identification of the deletion breakpoints allowed development of a simple tool for molecular testing of this genetic subtype of adRP.