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Adams PC, Jeffrey GP, Ryan J. Concerns about new proposals for haemochromatosis screening - Authors' reply. Lancet 2023; 402:692. [PMID: 37633668 DOI: 10.1016/s0140-6736(23)01504-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/27/2023] [Accepted: 07/17/2023] [Indexed: 08/28/2023]
Affiliation(s)
- Paul C Adams
- Department of Medicine, Schulich School of Medicine & Dentistry, Western University, London, ON N6A 5C1, Canada.
| | - Gary P Jeffrey
- Medical School, University of Western Australia, Perth, WA, Australia
| | - John Ryan
- Royal College of Surgeons of Ireland, Dublin, Ireland
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2
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Kalyta K, Stelmaszczyk W, Szczęśniak D, Kotuła L, Dobosz P, Mroczek M. The Spectrum of the Heterozygous Effect in Biallelic Mendelian Diseases-The Symptomatic Heterozygote Issue. Genes (Basel) 2023; 14:1562. [PMID: 37628614 PMCID: PMC10454578 DOI: 10.3390/genes14081562] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 07/26/2023] [Accepted: 07/27/2023] [Indexed: 08/27/2023] Open
Abstract
Heterozygous carriers of pathogenic/likely pathogenic variants in autosomal recessive disorders seem to be asymptomatic. However, in recent years, an increasing number of case reports have suggested that mild and unspecific symptoms can occur in some heterozygotes, as symptomatic heterozygotes have been identified across different disease types, including neurological, neuromuscular, hematological, and pulmonary diseases. The symptoms are usually milder in heterozygotes than in biallelic variants and occur "later in life". The status of symptomatic heterozygotes as separate entities is often disputed, and alternative diagnoses are considered. Indeed, often only a thin line exists between dual, dominant, and recessive modes of inheritance and symptomatic heterozygosity. Interestingly, recent population studies have found global disease effects in heterozygous carriers of some genetic variants. What makes the few heterozygotes symptomatic, while the majority show no symptoms? The molecular basis of this phenomenon is still unknown. Possible explanations include undiscovered deep-splicing variants, genetic and environmental modifiers, digenic/oligogenic inheritance, skewed methylation patterns, and mutational burden. Symptomatic heterozygotes are rarely reported in the literature, mainly because most did not undergo the complete diagnostic procedure, so alternative diagnoses could not be conclusively excluded. However, despite the increasing accessibility to high-throughput technologies, there still seems to be a small group of patients with mild symptoms and just one variant of autosomes in biallelic diseases. Here, we present some examples, the current state of knowledge, and possible explanations for this phenomenon, and thus argue against the existing dominant/recessive classification.
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Affiliation(s)
- Kateryna Kalyta
- School of Life Sciences, FHNW—University of Applied Sciences, 4132 Muttenz, Switzerland;
| | - Weronika Stelmaszczyk
- School of Cellular and Molecular Medicine, University of Bristol, Bristol BS8 1TD, UK;
| | - Dominika Szczęśniak
- Institute of Psychiatry and Neurology in Warsaw, Genetics Department, 02-957 Warsaw, Poland;
| | - Lidia Kotuła
- Department of Genetics, Medical University, 20-080 Lublin, Poland;
| | - Paula Dobosz
- Institute of Genetics and Biotechnology, Faculty of Biology, University of Warsaw, Pawinskiego 5A, 02-106 Warsaw, Poland;
| | - Magdalena Mroczek
- University Hospital Basel, University of Basel, 4031 Basel, Switzerland
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3
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Kersting N, Fontana JC, Athayde FPD, Carlotto FM, Machado BA, Araújo CDSRD, Sekine L, Onsten TGH, Leistner-Segal S. Hereditary hemochromatosis beyond hyperferritinemia: Clinical and laboratory investigation of the patient's profile submitted to phlebotomy in two reference centers in southern Brazil. Genet Mol Biol 2023; 46:e20220230. [PMID: 37216649 DOI: 10.1590/1678-4685-gmb-2022-0230] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2022] [Accepted: 01/23/2023] [Indexed: 05/24/2023] Open
Abstract
Hereditary Hemochromatosis is a disorder characterized by iron deposition in several organs and hyperferritinemia. The most studied variants are linked to the HFE gene. In Brazil, surveys that characterize this population are scarce, with no sampling in the state of Rio Grande do Sul. Our objective is to carry out a data collection focusing on the profile of this population and the influence of the most frequently HFE variants. Two centers were enrolled: Hospital de Clínicas de Porto Alegre and Hospital São Vicente de Paulo. Patients with hyperferritinemia and undergoing phlebotomy were invited. Clinical data were collected, including HFE investigation. Among the descriptive data, the allele frequency of the C282Y variant (0.252) stands out, which differs from the national scenario. Systemic arterial hypertension was the most cited comorbidity. Differences between centers were observed, highlighting higher frequency of H63D cases in HSVP (p<0.01). Genotypes were stratified according to deleterious effect of C282Y variant. Higher transferrin saturation and number of phlebotomies were observed in the C282Y/C282Y cases (p<0.001). Positive family history for hyperferritinemia was more prevalent in compound heterozygotes (p<0.01). The results presented confirm the importance of encouraging such studies and reiterate the need for greater attention to this population.
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Affiliation(s)
- Nathalia Kersting
- Universidade Federal do Rio Grande do Sul (UFRGS), Programa de Pós-Graduação em Medicina: Ciências Médicas, Porto Alegre, RS, Brazil
- Hospital de Clínicas de Porto Alegre (HCPA), Serviço de Genética Médica, Porto Alegre, RS, Brazil
| | - Juliana Cristine Fontana
- Hospital de Clínicas de Porto Alegre (HCPA), Serviço de Genética Médica, Porto Alegre, RS, Brazil
| | | | | | | | | | - Leo Sekine
- Universidade Federal do Rio Grande do Sul (UFRGS), Programa de Pós-Graduação em Medicina: Ciências Médicas, Porto Alegre, RS, Brazil
- Hospital de Clínicas de Porto Alegre, Serviço de Hemoterapia, Porto Alegre, RS, Brazil
- Universidade Federal do Rio Grande do Sul (UFRGS), Faculdade de Medicina (Famed), Departamento de Medicina Interna, Porto Alegre, RS, Brazil
| | - Tor Gunnar Hugo Onsten
- Hospital de Clínicas de Porto Alegre, Serviço de Hemoterapia, Porto Alegre, RS, Brazil
- Universidade Federal do Rio Grande do Sul (UFRGS), Faculdade de Medicina (Famed), Departamento de Medicina Interna, Porto Alegre, RS, Brazil
| | - Sandra Leistner-Segal
- Universidade Federal do Rio Grande do Sul (UFRGS), Programa de Pós-Graduação em Medicina: Ciências Médicas, Porto Alegre, RS, Brazil
- Hospital de Clínicas de Porto Alegre (HCPA), Serviço de Genética Médica, Porto Alegre, RS, Brazil
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Biallelic p.V37I variant in GJB2 is associated with increasing incidence of hearing loss with age. Genet Med 2022; 24:915-923. [PMID: 35016843 DOI: 10.1016/j.gim.2021.12.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Revised: 12/13/2021] [Accepted: 12/14/2021] [Indexed: 12/15/2022] Open
Abstract
PURPOSE This study aimed to quantitatively assess the incidence of hearing loss in relation to age in individuals with biallelic p.V37I variant in GJB2. METHODS Population screening of the biallelic p.V37I variant was performed in 30,122 individuals aged between 0 and 97 years in Shanghai. Hearing thresholds of the biallelic p.V37I individuals and the controls were determined by click auditory brainstem response or pure tone audiometry. RESULTS Biallelic p.V37I was detected in 0.528% (159/30,122) of the subjects. Of the biallelic p.V37I newborns, 43.91% (18/41) passed their distortion-product otoacoustic emissions-based newborn hearing screening or had hearing thresholds lower than 20 decible above normal hearing level. The older newborns had elevated hearing thresholds, with increasing incidence of 9.52%, 23.08%, 59.38%, and 80.00% for moderate or higher grade of hearing loss in age groups of 7 to 15 years, 20 to 40 years, 40 to 60 years, and 60 to 85 years, respectively. Their hearing deteriorated at a rate of 0.40 dB hearing level per year on average; males were more susceptible, and deterioration occurred preferentially at higher sound frequencies. CONCLUSION The biallelic p.V37I variant is associated with steadily progressive hearing loss with increasing incidence over the course of life. Most of the biallelic p.V37I individuals may develop significant hearing loss in adulthood and, can benefit from early diagnosis and intervention through wide-spread genetic screening.
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Xiao Q, Lauschke VM. The prevalence, genetic complexity and population-specific founder effects of human autosomal recessive disorders. NPJ Genom Med 2021; 6:41. [PMID: 34078906 PMCID: PMC8172936 DOI: 10.1038/s41525-021-00203-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2021] [Accepted: 05/05/2021] [Indexed: 11/13/2022] Open
Abstract
Autosomal recessive (AR) disorders pose a significant burden for public health. However, despite their clinical importance, epidemiology and molecular genetics of many AR diseases remain poorly characterized. Here, we analyzed the genetic variability of 508 genes associated with AR disorders based on sequencing data from 141,456 individuals across seven ethnogeographic groups by integrating variants with documented pathogenicity from ClinVar, with stringent functionality predictions for variants with unknown pathogenicity. We first validated our model using 85 diseases for which population-specific prevalence data were available and found that our estimates strongly correlated with the respective clinically observed disease frequencies (r = 0.68; p < 0.0001). We found striking differences in population-specific disease prevalence with 101 AR diseases (27%) being limited to specific populations, while an additional 305 diseases (68%) differed more than tenfold across major ethnogeographic groups. Furthermore, by analyzing genetic AR disease complexity, we confirm founder effects for cystic fibrosis and Stargardt disease, and provide strong evidences for >25 additional population-specific founder mutations. The presented analyses reveal the molecular genetics of AR diseases with unprecedented resolution and provide insights into epidemiology, complexity, and population-specific founder effects. These data can serve as a powerful resource for clinical geneticists to inform population-adjusted genetic screening programs, particularly in otherwise understudied ethnogeographic groups.
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Affiliation(s)
- Qingyang Xiao
- Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
| | - Volker M Lauschke
- Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
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Garmany R, Lee CJ, Sharp RR, Kullo IJ. Failure to follow up on a medically actionable finding from direct to consumer genetic testing: A case report. Mol Genet Genomic Med 2020; 8:e1252. [PMID: 32329251 PMCID: PMC7284021 DOI: 10.1002/mgg3.1252] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Revised: 10/14/2019] [Accepted: 10/23/2019] [Indexed: 01/21/2023] Open
Abstract
BACKGROUND A 61-year-old woman underwent direct to consumer genetic testing and was found to be homozygous for the C282Y HFE variant (c.845G>A :p.Cys282Tyr) which is classified as pathogenic/likely pathogenic for hereditary hemochromatosis. However, no action was taken by the individual. METHODS The individual took part in the Mayo Clinic Return of Actionable Variants Empiric (RAVE) study and the actionable finding was confirmed and results disclosed in person by a genetic counselor with subsequent referral to a hepatologist. RESULTS Further testing revealed iron overload with an elevated ferritin level (560 ng/ml) and increased ferritin saturation (74%). Phlebotomy was initiated with subsequent normalization of the ferritin levels (252 ng/ml). CONCLUSION This case highlights that actionable genetic results may not be acted on after direct to consumer testing and the need for effective genetic counseling after such testing.
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Affiliation(s)
- Ramin Garmany
- Department of Cardiovascular Medicine, Mayo Clinic, Rochester, MN, USA
| | - Christopher J Lee
- Department of Cardiovascular Medicine, Mayo Clinic, Rochester, MN, USA
| | - Richard R Sharp
- Biomedical Ethics Research Program, Mayo Clinic, Rochester, MN, USA
| | - Iftikhar J Kullo
- Department of Cardiovascular Medicine, Mayo Clinic, Rochester, MN, USA
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Wierbowski SD, Fragoza R, Liang S, Yu H. Extracting Complementary Insights from Molecular Phenotypes for Prioritization of Disease-Associated Mutations. CURRENT OPINION IN SYSTEMS BIOLOGY 2018; 11:107-116. [PMID: 31086831 PMCID: PMC6510504 DOI: 10.1016/j.coisb.2018.09.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Rapid advances in next-generation sequencing technology have resulted in an explosion of whole-exome/genome sequencing data, providing an unprecedented opportunity to identify disease- and trait-associated variants in humans on a large scale. To date, the long-standing paradigm has leveraged fitness-based approximations to translate this ever-expanding sequencing data into causal insights in disease. However, while this approach robustly identifies variants under evolutionary constraint, it fails to provide molecular insights. Moreover, complex disease phenomena often violate standard assumptions of a direct organismal phenotype to overall fitness effect relationship. Here we discuss the potential of a molecular phenotype-oriented paradigm to uniquely identify candidate disease-causing mutations from the human genetic background. By providing a direct connection between single nucleotide mutations and observable organismal and cellular phenotypes associated with disease, we suggest that molecular phenotypes can readily incorporate alongside established fitness-based methodologies to provide complementary insights to the functional impact of human mutations. Lastly, we discuss how integrated approaches between molecular phenotypes and fitness-based perspectives facilitate new insights into the molecular mechanisms underlying disease-associated mutations while also providing a platform for improved interpretation of epistasis in human disease.
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Affiliation(s)
- Shayne D. Wierbowski
- Department of Biological Statistics and Computational Biology, Cornell University, Ithaca, NY 14853, USA
- Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
| | - Robert Fragoza
- Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Siqi Liang
- Department of Biological Statistics and Computational Biology, Cornell University, Ithaca, NY 14853, USA
- Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
| | - Haiyuan Yu
- Department of Biological Statistics and Computational Biology, Cornell University, Ithaca, NY 14853, USA
- Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA
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8
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Shah N, Hou YCC, Yu HC, Sainger R, Caskey CT, Venter JC, Telenti A. Identification of Misclassified ClinVar Variants via Disease Population Prevalence. Am J Hum Genet 2018; 102:609-619. [PMID: 29625023 DOI: 10.1016/j.ajhg.2018.02.019] [Citation(s) in RCA: 87] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Accepted: 02/22/2018] [Indexed: 01/07/2023] Open
Abstract
There is a significant interest in the standardized classification of human genetic variants. We used whole-genome sequence data from 10,495 unrelated individuals to contrast population frequency of pathogenic variants to the expected population prevalence of the disease. Analyses included the ACMG-recommended 59 gene-condition sets for incidental findings and 463 genes associated with 265 OrphaNet conditions. A total of 25,505 variants were used to identify patterns of inflation (i.e., excess genetic risk and misclassification). Inflation increases as the level of evidence supporting the pathogenic nature of the variant decreases. We observed up to 11.5% of genetic disorders with inflation in pathogenic variant sets and up to 92.3% for the variant set with conflicting interpretations. This improved to 7.7% and 57.7%, respectively, after filtering for disease-specific allele frequency. The patterns of inflation were replicated using public data from more than 138,000 genomes. The burden of rare variants was a main contributing factor of the observed inflation, indicating collective misclassified rare variants. We also analyzed the dynamics of re-classification of variant pathogenicity in ClinVar over time, which indicates progressive improvement in variant classification. The study shows that databases include a significant proportion of wrongly ascertained variants; however, it underscores the critical role of ClinVar to contrast claims and foster validation across submitters.
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9
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Grosse SD, Gurrin LC, Bertalli NA, Allen KJ. Clinical penetrance in hereditary hemochromatosis: estimates of the cumulative incidence of severe liver disease among HFE C282Y homozygotes. Genet Med 2018; 20:383-389. [PMID: 28771247 PMCID: PMC5797490 DOI: 10.1038/gim.2017.121] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2017] [Accepted: 06/07/2017] [Indexed: 12/28/2022] Open
Abstract
Iron overload (hemochromatosis) can cause serious, symptomatic disease that is preventable if detected early and managed appropriately. The leading cause of hemochromatosis in populations of predominantly European ancestry is homozygosity of the C282Y variant in the HFE gene. Screening of adults for iron overload or associated genotypes is controversial, largely because of a belief that severe phenotypes are uncommon, although cascade testing of first-degree relatives of patients is widely endorsed. We contend that severe liver disease (cirrhosis or hepatocellular cancer) is not at all uncommon among older males with hereditary hemochromatosis. Our review of the published data from a variety of empirical sources indicates that roughly 1 in 10 male HFE C282Y homozygotes is likely to develop severe liver disease during his lifetime unless iron overload is detected early and treated. New evidence from a randomized controlled trial of treatment allows for evidence-based management of presymptomatic patients. Although population screening for HFE C282Y homozygosity faces multiple barriers, a potentially effective strategy for increasing the early detection and prevention of clinical iron overload and severe disease is to include HFE C282Y homozygosity in lists of medically actionable gene variants when reporting the results of genome or exome sequencing.
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Affiliation(s)
- Scott D. Grosse
- National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
| | - Lyle C. Gurrin
- Department of Gut and Liver, Murdoch Childrens Research Institute, Melbourne, Victoria, Australia
- Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, University of Melbourne, Melbourne, Victoria, Australia
| | - Nadine A. Bertalli
- Department of Gut and Liver, Murdoch Childrens Research Institute, Melbourne, Victoria, Australia
- Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, University of Melbourne, Melbourne, Victoria, Australia
| | - Katrina J. Allen
- Department of Gut and Liver, Murdoch Childrens Research Institute, Melbourne, Victoria, Australia
- Department of Paediatrics, University of Melbourne, Melbourne, Victoria, Australia
- Department of Gastroenterology, Royal Children’s Hospital, Melbourne, Victoria, Australia
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10
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Kawabata H. The mechanisms of systemic iron homeostasis and etiology, diagnosis, and treatment of hereditary hemochromatosis. Int J Hematol 2017; 107:31-43. [PMID: 29134618 DOI: 10.1007/s12185-017-2365-3] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2017] [Accepted: 11/08/2017] [Indexed: 02/06/2023]
Abstract
Hereditary hemochromatosis (HH) is a group of genetic iron overload disorders that manifest with various symptoms, including hepatic dysfunction, diabetes, and cardiomyopathy. Classic HH type 1, which is common in Caucasians, is caused by bi-allelic mutations of HFE. Severe types of HH are caused by either bi-allelic mutations of HFE2 that encodes hemojuvelin (type 2A) or HAMP that encodes hepcidin (type 2B). HH type 3, which is of intermediate severity, is caused by bi-allelic mutations of TFR2 that encodes transferrin receptor 2. Mutations of SLC40A1 that encodes ferroportin, the only cellular iron exporter, causes either HH type 4A (loss-of-function mutations) or HH type 4B (gain-of-function mutations). Studies on these gene products uncovered a part of the mechanisms of the systemic iron regulation; HFE, hemojuvelin, and TFR2 are involved in iron sensing and stimulating hepcidin expression, and hepcidin downregulates the expression of ferroportin of the target cells. Phlebotomy is the standard treatment for HH, and early initiation of the treatment is essential for preventing irreversible organ damage. However, because of the rarity and difficulty in making the genetic diagnosis, a large proportion of patients with non-HFE HH might have been undiagnosed; therefore, awareness of this disorder is important.
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Affiliation(s)
- Hiroshi Kawabata
- Department of Hematology and Immunology, Kanazawa Medical University, 1-1 Daigaku, Uchinada-machi, Ishikawa-ken, 920-0293, Japan.
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11
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Braseth TA, Hervig T, Rosvik AS. Hemochromatosis and blood donation. Transfus Apher Sci 2017; 56:485-489. [PMID: 28610845 DOI: 10.1016/j.transci.2017.05.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The voluntary, unpaid, altruistic blood donor is a cornerstone of current transfusion medicine. The complexity of medical and ethical issues related to blood donation and hemochromatosis has led to a large number of studies related to the safety of the hemochromatosis donor and the quality of the blood components produced from these donations. The issue of accepting persons with HC as blood donors is diverting, both in Europe and worldwide and without joint guidelines. A questionnaire-based study was performed and mailed to all 25 blood bank leaders in Norway. Descriptive analysis was used to evaluate the data. Eight of 22 blood banks strictly followed national guidelines concerning persons with hemochromatosis. Other blood banks make local adjustments. 16 of 22 responding blood banks accept hemochromatosis donors and five do not, and one answered partly yes. The reasons the blood bank leaders supported the acceptance of hemochromatosis donors differ. Based on published papers and the present questionnaire, we believe that a clear definition of the "hemochromatosis donor" and guidelines with more detailed information on an acceptable donation regime would be important to overcome the weak points in blood donor eligibility criteria.
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Affiliation(s)
- Turid Aarhus Braseth
- Faculty of Engineering and Business Administration, Department of Biomedical Laboratory Sciences and Chemical Engineering, Bergen University College, pb 7030, 5020 Bergen, Norway; Western Norway University of Applied Sciences, Postbox 7030, 5020 Bergen, Norway
| | - Tor Hervig
- Institute of Clinical Sciences, University of Bergen, 5021 Bergen, Norway; Department of Immunology and transfusion medicine, Haukeland University Hospital, 5021 Bergen, Norway.
| | - Anne Synnove Rosvik
- Department of Biological Sciences Aalesund, Faculty of Natural Sciences and Technology, The Norwegian University of Science and Technology (NTNU) in Aalesund, PB1517, N-6025 Aalesund, Norway
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12
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Kudin AP, Baron G, Zsurka G, Hampel KG, Elger CE, Grote A, Weber Y, Lerche H, Thiele H, Nürnberg P, Schulz H, Ruppert AK, Sander T, Cheng Q, Arnér ES, Schomburg L, Seeher S, Fradejas-Villar N, Schweizer U, Kunz WS. Homozygous mutation in TXNRD1 is associated with genetic generalized epilepsy. Free Radic Biol Med 2017; 106:270-277. [PMID: 28232204 DOI: 10.1016/j.freeradbiomed.2017.02.040] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Revised: 02/10/2017] [Accepted: 02/20/2017] [Indexed: 11/16/2022]
Abstract
Increased oxidative stress has been widely implicated in the pathogenesis in various forms of human epilepsy. Here, we report a homozygous mutation in TXNRD1 (thioredoxin reductase 1) in a family with genetic generalized epilepsy. TXNRD1 is an essential selenium-containing enzyme involved in detoxification of reactive oxygen species (ROS) and redox signaling. The TXNRD1 mutation p.Pro190Leu affecting a highly conserved amino acid residue was identified by whole-exome sequencing of blood DNA from the index patient. The detected mutation and its segregation within the family - all siblings of the index patient were homozygous and the parents heterozygous - were confirmed by Sanger sequencing. TXNRD1 activity was determined in subcellular fractions from a skeletal muscle biopsy and skin fibroblasts of the index patient and the expression levels of the mutated protein were assessed by 75Se labeling and Western blot analysis. As result of the mutation, the activity of TXNRD1 was reduced in the patient's fibroblasts and skeletal muscle (to 34±3% and 16±8% of controls, respectively). In fibroblasts, we detected reduced 75Se-labeling of the enzyme (41±3% of controls). An in-depth in vitro kinetic analysis of the recombinant mutated TXNRD1 indicated 30-40% lowered kcat/Se values. Therefore, a reduced activity of the enzyme in the patient's tissue samples is explained by (i) lower enzyme turnover and (ii) reduced abundance of the mutated enzyme as confirmed by Western blotting and 75Se labeling. The mutant fibroblasts were also found to be less resistant to a hydrogen peroxide challenge. Our data agree with a potential role of insufficient ROS detoxification for disease manifestation in genetic generalized epilepsy.
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Affiliation(s)
- Alexei P Kudin
- Department of Epileptology and Life & Brain Center, University of Bonn, Bonn, Germany.
| | - Gregor Baron
- Department of Epileptology and Life & Brain Center, University of Bonn, Bonn, Germany.
| | - Gábor Zsurka
- Department of Epileptology and Life & Brain Center, University of Bonn, Bonn, Germany.
| | - Kevin G Hampel
- Department of Epileptology and Life & Brain Center, University of Bonn, Bonn, Germany.
| | - Christian E Elger
- Department of Epileptology and Life & Brain Center, University of Bonn, Bonn, Germany.
| | - Alexander Grote
- Department of Neurosurgery, University of Bonn, Bonn, Germany.
| | - Yvonne Weber
- Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany.
| | - Holger Lerche
- Department of Neurology and Epileptology, Hertie Institute for Clinical Brain Research, University of Tübingen, Tübingen, Germany.
| | - Holger Thiele
- Cologne Center for Genomics, University of Cologne, Cologne, Germany.
| | - Peter Nürnberg
- Cologne Center for Genomics, University of Cologne, Cologne, Germany.
| | - Herbert Schulz
- Cologne Center for Genomics, University of Cologne, Cologne, Germany.
| | | | - Thomas Sander
- Cologne Center for Genomics, University of Cologne, Cologne, Germany.
| | - Qing Cheng
- Division of Biochemistry, Dept. Medical Biochemistry and Biophysics (MBB), Karolinska Institutet, Stockholm, Sweden.
| | - Elias Sj Arnér
- Division of Biochemistry, Dept. Medical Biochemistry and Biophysics (MBB), Karolinska Institutet, Stockholm, Sweden.
| | - Lutz Schomburg
- Institute of Experimental Endocrinology, Charité-Universitätsmedizin, Berlin, Germany.
| | - Sandra Seeher
- Institut für Biochemie und Molekularbiologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Germany.
| | - Noelia Fradejas-Villar
- Institut für Biochemie und Molekularbiologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Germany.
| | - Ulrich Schweizer
- Institut für Biochemie und Molekularbiologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Germany.
| | - Wolfram S Kunz
- Department of Epileptology and Life & Brain Center, University of Bonn, Bonn, Germany.
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Delanghe JR, Speeckaert MM, De Buyzere ML. The evolutionary adaptation of hemochromatosis associated mutations during the neolithic. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 2016; 161:530-531. [PMID: 27348451 DOI: 10.1002/ajpa.23045] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Accepted: 06/12/2016] [Indexed: 11/07/2022]
Affiliation(s)
- Joris R Delanghe
- Department of Clinical chemistry, Ghent University, Ghent, Belgium.
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14
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Association Studies of HFE C282Y and H63D Variants with Oral Cancer Risk and Iron Homeostasis Among Whites and Blacks. Cancers (Basel) 2015; 7:2386-96. [PMID: 26690219 PMCID: PMC4695898 DOI: 10.3390/cancers7040898] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Revised: 10/25/2015] [Accepted: 12/02/2015] [Indexed: 01/29/2023] Open
Abstract
Background: Polymorphisms in the hemochromatosis (HFE) gene are associated with excessive iron absorption from the diet, and pro-oxidant effects of iron accumulation are thought to be a risk factor for several types of cancer. Methods: The C282Y (rs1800562) and H63D (rs1799945) polymorphisms were genotyped in 301 oral cancer cases and 437 controls and analyzed in relation to oral cancer risk, and serum iron biomarker levels from a subset of 130 subjects. Results: Individuals with the C282Y allele had lower total iron binding capacity (TIBC) (321.2 ± 37.2 µg/dL vs. 397.7 ± 89.0 µg/dL, p = 0.007) and higher percent transferrin saturation (22.0 ± 8.7 vs. 35.6 ± 22.9, p = 0.023) than wild type individuals. Iron and ferritin levels approached significantly higher levels for the C282Y allele (p = 0.0632 and p = 0.0588, respectively). Conclusions: Iron biomarker levels were elevated by the C282Y allele, but neither (rs1800562) nor (rs1799945) was associated with oral cancer risk in blacks and whites.
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Abstract
Hereditary hemochromatosis is a rare genetic disorder that can have significant clinical consequences. Hemochromatosis is associated with iron overload, and can initially be recognized through laboratory testing for serum ferritin and transferrin saturation. Genetic testing for the HFE mutation can be performed in patients with elevated iron indices and a suspicion for hemochromatosis or liver disease. The main pathway resulting in iron overload is through altered hepcidin levels. Treatment of patients with the clinical phenotype of hereditary hemochromatosis is commonly through phlebotomy for removal of excess iron stores. This article highlights the current information and data regarding the diagnosis and management of hemochromatosis.
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Abstract
Hereditary hemochromatosis and Wilson disease are autosomal recessive storage disorders of iron and copper overload, respectively. These metals are involved in multiple redox reactions, and their abnormal accumulation can cause significant injury in the liver and other organs. Over the last few decades clinicians have developed a much better understanding of these metals and their mechanism of action. Moreover, sophisticated molecular genetic testing techniques that make diagnostic testing less invasive are now available. This article updates and discusses the pathogenesis, diagnosis, and management of these metal storage disorders.
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Affiliation(s)
- Pushpjeet Kanwar
- Liver Center of Excellence, Department of Gastroenterology, Digestive Disease Institute, Virginia Mason Medical Center, 1100 9th Avenue, Mailstop C3-GAS, Seattle, WA 98101, USA
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Cooper DN, Krawczak M, Polychronakos C, Tyler-Smith C, Kehrer-Sawatzki H. Where genotype is not predictive of phenotype: towards an understanding of the molecular basis of reduced penetrance in human inherited disease. Hum Genet 2013; 132:1077-130. [PMID: 23820649 PMCID: PMC3778950 DOI: 10.1007/s00439-013-1331-2] [Citation(s) in RCA: 417] [Impact Index Per Article: 37.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Accepted: 06/15/2013] [Indexed: 02/06/2023]
Abstract
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.
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Affiliation(s)
- David N. Cooper
- Institute of Medical Genetics, School of Medicine, Cardiff University, Heath Park, Cardiff, CF14 4XN UK
| | - Michael Krawczak
- Institute of Medical Informatics and Statistics, Christian-Albrechts University, 24105 Kiel, Germany
| | | | - Chris Tyler-Smith
- The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SA UK
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Abstract
Hereditary hemochromatosis is an inherited iron overload disorder caused by inappropriately low hepcidin secretion leading to increased duodenal absorption of dietary iron, most commonly in C282Y homozygous individuals. This can result in elevated serum ferritin, iron deposition in various organs and ultimately end-organ damage, although there is incomplete biochemical and clinical penetrance and variable phenotypic expression of the HFE mutation in hereditary hemochromatosis. An elevated SF >1000 mg/l [corrected] is associated with an increased risk of cirrhosis and mortality in C282Y homozygotes.Conversely, a SF <1000 µg/l is associated with a very low likelihood of cirrhosis, making liver biopsy unnecessary among C282Y homozygotes in the absence of concomitant risk factors for liver disease. Phlebotomy remains the mainstay of treatment and new treatments being studied include erythrocytapheresis and 'mini-hepcidins'. Iron overload is being recognized to play a carcinogenic role in hepatocellular carcinoma and other cancers, possibly supporting iron depletion in these patients.
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Affiliation(s)
- Pushpjeet Kanwar
- Liver Center for Excellence, Digestive Disease Institute, Virginia Mason Medical Center, Seattle, WA, USA
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Deleterious- and disease-allele prevalence in healthy individuals: insights from current predictions, mutation databases, and population-scale resequencing. Am J Hum Genet 2012; 91:1022-32. [PMID: 23217326 DOI: 10.1016/j.ajhg.2012.10.015] [Citation(s) in RCA: 197] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2012] [Revised: 08/22/2012] [Accepted: 10/11/2012] [Indexed: 12/19/2022] Open
Abstract
We have assessed the numbers of potentially deleterious variants in the genomes of apparently healthy humans by using (1) low-coverage whole-genome sequence data from 179 individuals in the 1000 Genomes Pilot Project and (2) current predictions and databases of deleterious variants. Each individual carried 281-515 missense substitutions, 40-85 of which were homozygous, predicted to be highly damaging. They also carried 40-110 variants classified by the Human Gene Mutation Database (HGMD) as disease-causing mutations (DMs), 3-24 variants in the homozygous state, and many polymorphisms putatively associated with disease. Whereas many of these DMs are likely to represent disease-allele-annotation errors, between 0 and 8 DMs (0-1 homozygous) per individual are predicted to be highly damaging, and some of them provide information of medical relevance. These analyses emphasize the need for improved annotation of disease alleles both in mutation databases and in the primary literature; some HGMD mutation data have been recategorized on the basis of the present findings, an iterative process that is both necessary and ongoing. Our estimates of deleterious-allele numbers are likely to be subject to both overcounting and undercounting. However, our current best mean estimates of ~400 damaging variants and ~2 bona fide disease mutations per individual are likely to increase rather than decrease as sequencing studies ascertain rare variants more effectively and as additional disease alleles are discovered.
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