Abstract
Denmark has an extensive collection of national and regional medical registries. There are many advantages to registry-based research when investigating genetic diseases which, due to their rarity, can be difficult to identify. In this study, we aimed to provide an updated overview of Danish registries for medical genetic conditions and describe how data linkage across registries can be used to collect data on genetic diseases at the individual level and at the family level. We present a list of medical genetic registries in Denmark at the national level, data sources from the departments of clinical genetics and other specialized centers, and project-specific data sources. We also summarize key general registries, such as the Danish National Registry of Patients, the Danish Medical Birth Registry, and the Civil Registration System, which are renowned for their comprehensive and high quality data, and are useful supplemental data sources for genetic epidemiology research. We describe the potential for data linkage across multiple registries, which allows for access to medical histories with follow-up time spanning birth to death. Finally, we provide a brief introduction to the Danish epidemiological research setting and legalities related to data access. The Danish collection of medical registries is a valuable resource for genetic epidemiology research.
Introduction
In many countries, identifying persons with a genetic condition in the background population can be difficult due to the rarity of genetic diseases, diagnostic challenges, and lack of systematic registration. The task can be akin to finding a “needle in a haystack,” often requiring multidisciplinary and cross-national efforts. Denmark, however, has an extensive collection of medical and administrative registries and databases that provide a unique opportunity to collect patient data at the individual level routinely, in some cases at the family level, and to carry out reliable kinship tracking.Citation1,Citation2 A registry-based research approach has many advantages, particularly when investigating inheritable conditions. Cohorts can be assembled relatively quickly and relevant medical histories can be obtained by linking data from multiple data sources.
In 1982, Broeng-Nielsen et al compiled a bibliography entitled “Danish Family Studies of Medical Genetic Disorders 1927–1980”.Citation3 In this work, 672 bibliographic references covering 344 genetic disorders were identified, along with seven medical registries (which were listed, without providing details). To our knowledge, no updated compilation of Danish genetic data sources has been made since then. Therefore, we set out to provide an updated overview of Danish registries for medical genetic conditions; describe how data linkage across registries can be used to collect data on genetic diseases at the individual level and at the family level; and provide a brief introduction to the Danish epidemiological research setting and legalities related to data access.
Materials and methods
Danish health care infrastructure
The Danish health care system provides equal access to medical care for all residents. Approximately 85% of Danish health care is tax-funded, with the remaining 15% paid out-of-pocket.Citation4 General practitioners are gatekeepers, providing referrals to specialists when appropriate, and the majority of specialist care is hospital-based. Contacts to the primary (ie, general practitioners) and secondary (ie, hospitals) health care sectors are registered, as are prescriptions redeemed at outpatient pharmacies.Citation4 The treating physician/department is responsible for reporting data to the relevant registry, and reporting primarily occurs electronically and automatically. Funding by the national government for services rendered is based on the registration and coding of services provided at each health care site. Therefore, the Danish health care system is conducive to completeness of registration. Each person in Denmark is issued a unique personal (CPR) identification number upon birth or immigration. The CPR number encodes, amongst other things, date of birth and gender, and is the means by which information on a given individual can be merged unambiguously from multiple data sources.Citation5 Thus, the Danish health care system has a long tradition of high quality longitudinal registry data, in a setting of universal health care access.
Identification of medical registries for genetic diseases
We sent inquiries for medical data sources on genetic diseases with the potential to be used in registry-based research to relevant registry administrators, hospital departments (eg, departments of clinical genetics, pediatrics, and dermatology), specialized medical centers (eg, Center for Rare Diseases [Center for Sjældne Sygdomme], Clinic for Rare Handicaps [Klinik for Sjældne Handicaps], and Centre for Oral Health in Rare Diseases [Odontologisk Videncenter]), governmental agencies (eg, the Danish Health and Medicines Authority [Sundhedsstyrelsen], and the Danish Data Protection Agency [Datatilsynet]), and performed Internet-based searches. Once identified, we contacted key registry administrators for updated information and verification of the status of a given registry. Information on biobanks was considered beyond the scope of this work, and is therefore not included (with the exception of the Danish Newborn Screening Biobank and Registry,Citation6 which can be considered as both a registry and a biobank).
Data sources for genetic epidemiology research
We identified 29 potential medical data sources for genetic research and a further 12 hospital departments and specialized centers. The data sources are summarized in – and categorized into four main groups: national registries (); data from hospital departments and centers (); project-specific data sources established in relation to various research projects, eg, PhD dissertations (); and supplemental registries for data linkage and collection of medical histories ().
Table 1 Overview of national medical genetic registries in Denmark
Table 2 Danish departments of clinical genetics and other specialized departments and centers
Table 3 Examples of project-specific data sources established in relation to past research projects, eg, PhD dissertations
Table 4 Supplemental registries for data linkage and collection of medical histories
In the following section, we list examples of well established genetic and supplemental data sources. Despite our best efforts to achieve completeness, we recognize that this may not be an exhaustive list detailing all existing genetic registries in Denmark.
National registries ()
Danish cytogenetic central register
The Danish Cytogenetic Central Register is a nationwide registry of all karyotypes done prenatally and postnatally since the advent of cytogenetic analysis in the early 1960s. The register holds over 300,000 total registrations with approximately 10,000 new registrations each year.Citation7,Citation8 The register also contains information on specific genetic diseases, such as Fragile-X, Prader-Willi, and Angelman syndromes. The primary purpose of this register is to gather prenatal and postnatal data for the study of trends in prenatal diagnostics and chromosomal aberrations, including type and prevalence. The Danish Cytogenetic Central Register has been an important data source for the study of monosomy X and trisomy 13, 18, and 21, in addition to other research projects.Citation9,Citation10
Genetic cancer registries
The Hereditary Nonpolyposis Colorectal Cancer Register and Hereditary Breast and Ovarian Cancer Registry are two examples of national registries for inheritable cancer risk. Data registration occurs systematically and nationwide. The Hereditary Nonpolyposis Colorectal Cancer RegisterCitation11,Citation12 was established in 1991, with nationwide data collection since 1995. The Hereditary Breast and Ovarian Cancer Registry was established in 1999. Both registers collect data on index cancer cases and relatives at risk (eg, referred on to specialist evaluation because of an accumulation of relatives with specific cancers or very young individuals with cancer). The Hereditary Breast and Ovarian Cancer Registry operates under the auspices of the Danish Breast Cancer Cooperative Group and is part of an umbrella clinical database that was established by the Danish Breast Cancer Cooperative Group in the late 1970s.Citation13 Numerous publications have arisen from data stemming from both registries.Citation13,Citation14
The Danish Cancer Registry (DCR) has recorded solid tumor cancers in Denmark since 1943, with mandatory reporting since 1987.Citation15–Citation17 Sites of malignancy are recorded using International Classification of Diseases diagnosis codes, 10th revision (ICD-10).Citation18 The DCR is an important data source for identifying heritable cancer risk. Former disease-specific registries, such as the Retinoblastoma Registry, can presently be found as data merged within the DCR.Citation19
Registries for specific genetic diseases
The Danish Huntington’s Register is an example of a nationwide, disease-specific registry that has been tracking Danish patients with Huntington’s chorea since 1940 via pedigrees and genetic testing.Citation20 This register was converted to electronic records in 1980 and has over 12,000 registrations of subjects either known to have Huntington’s disease or at risk of developing the disease. Both living and deceased individuals are registered.Citation21 This registry has been used to study crime among patients with Huntington’s disease as well as other research topics.Citation21,Citation22 The Danish Huntington’s Register also contributes data to the European Huntington’s Disease Network Registry.Citation23
The Danish Cystic Fibrosis Patient Registry is another example of a well established, disease-specific registry.Citation24 It was established in 2001 and had 451 cystic fibrosis cases registered as of December 31, 2009 (ie, all patients with cystic fibrosis in Denmark, both living and deceased). This registry contributes data to the European Cystic Fibrosis Society Patient RegistryCitation25 and serves as an important data source for ongoing research.Citation26
The Danish Family Archive for Genetic Eye Diseases (Dansk Familiearkiv for Arvelige Øjensygdomme) started around 1985 as a nonelectronic register at the National Eye Clinic (Statens Øjenklinik). It is a nationwide umbrella registry of heritable eye diseases, with over 100 different conditions represented, including retinitis pigmentosa, which has its own subregistry (see ). To date, there are over 100 published studies based on data from this registry, including studies on X-linked ocular albinism and retinitis pigmentosa.Citation27,Citation28
Neonatal registries
The National Registry of Congenital Malformations registers all congenital malformations detected during the first year of life, with data registration from 1983 to 1995.Citation29 During this period, all diagnosing physicians were required to register and illustrate (by free drawing) all structural congenital abnormalities (eg, congenital heart valve defects, cleft lip, and/or cleft palate), making these registrations very detailed and specific. Despite this, the registry is unfortunately known to have incomplete data.Citation30 From 1996 and onwards, congenital malformations have been electronically reported to the Danish National Registry of Patients (DNRP)Citation7 and can be identified using the corresponding ICD-10 codes.Citation18 Recent epidemiological studies have data on congenital malformations directly from the DNRP.Citation31 Since not all birth defects are due to chromosomal abnormalities, this particular neonatal registry is unique in that it provides data on structural congenital abnormalities. Other relevant registries with perinatal/neonatal data include the Danish Medical Birth RegistryCitation32 (see section on data linkage), the National Fetal Medicine Database,Citation33 and the Danish Newborn Screening Biobank and RegistryCitation6 (see ).
Data from the Danish departments of clinical genetics ()
In Denmark, the vast majority of genetic investigations and genetic counseling are undertaken at hospital departments of clinical genetics, located in the cities of Aalborg, Aarhus, Odense, Vejle, and Copenhagen. These departments store data on patients and families seen in the genetic outpatient clinics and/or investigated at clinical genetics laboratories. For instance, as of 2012, there were over 20,000 patients registered at the Department of Clinical Genetics, Aarhus University Hospital alone.
The departments of clinical genetics in Aarhus, Odense, and Aalborg currently use the Langtved databaseCitation34 to register and store patient data, primarily for genetic counseling. The Langtved database uses ICD-10 codes to encode broad categories of familial diseases, internal conventions determined by senior geneticists, and the internationally used McKusick codes.Citation35 Data are also registered in pedigrees (eg, the Cyrilic database, used from 1993 to 2013, and the PASS Clinical® genetic databaseCitation36 used from 2013). shows further relevant departments and centers in Denmark.
Project-specific data sources ()
Data from completed PhD dissertations or clinical studies are other important data sources. It is here that many hours of “field work” finding and meeting patients with rare genetic diseases have taken place, and from which future studies can expand upon (see ). The annotated bibliography published by Broeng-Nielsen et al is a historical list of over 600 genetic studies conducted up until 1980. The Danish National Research Database (www.forskningsdatabasen.dk) contains a public list of Danish research projects from which past PhD dissertations can be queried, as well as conference publications and scientific articles.Citation37 The established projects can be a springboard for future studies, with the advantage of having pre-established patient cohorts.
In 1980, Broeng-Nielsen et al warned about the potential loss of valuable pedigree data upon retirement or death of the principal investigators listed in the bibliography.Citation3 Data from more than half of the studies listed in this annotated bibliography were stored by individual investigators, many of them close to retirement age. Therefore, the establishment and maintenance of numerous genetic registries over recent decades has had an important role in the conservation of medical genetic data. Owing to this, several Danish genetic registries contain pedigrees and cohorts that span several generations. In the following section, we illustrate project-specific data sources with two examples, ie, the neurofibromatosis 1 cohort and the X-linked hypohidrotic ectodermal dysplasia cohort.
Neurofibromatosis 1 cohort
Neurofibromatosis 1, also known as von Recklinghausen disease, is an autosomal dominant condition with varying clinical manifestations, including characteristic café-au-lait spots in the skin and neurofibromas. The Borberg cohort of patients with neurofibromatosis 1 was established in 1940Citation38 and reinvestigated in a follow-up study 46 years later. Sørensen et alCitation39 revisited this established cohort and linked to data from the DCR to follow patients for the development of malignant neoplasms after diagnosis of neurofibromatosis 1. The registry-based approach was also used in the same study to investigate risk factors and survival.
X-linked hypohidrotic ectodermal dysplasia cohort
XLHED is a monogenetic condition affecting the skin, hair, and teeth. Using CPR numbers, data were collected from the relevant clinical departments, the Statens Centrale Odontologiske Register (SCOR) database,Citation40 the DNRP, and the Civil Registration System.Citation41 A cohort of 1224 persons was assembled, and population-based prevalence estimates and frequency of clinical features were calculated.Citation42 Patients with X-linked hypohidrotic ectodermal dysplasia (XLHED) (ie, gene tested and/or clinically diagnosed) were identified by inquiry at the relevant departments. The DNRP and SCOR database were then searched to identify additional cases by finding patients with a clinical diagnosis of XLHED and cardinal features associated with the condition (eg, skin, hair, and teeth disorders). The cohort can be expanded by linking to the Danish Medical Birth Registry to identify additional obligate carriers. This cohort can be used for future studies of disease incidence, mortality, and other outcomes.
Supplemental registries for data linkage and the collection of medical histories ()
The DNRP,Citation43 the Civil Registration System,Citation41 the DCR,Citation15 the Danish Medical Birth Registry,Citation32 and the National Pathology RegistryCitation44 are examples of major nationwide medical and administrative registries that can be used as supplemental data sources in epidemiologic studies of genetic diseases ().
The DNRP is a nationwide patient registry of diagnoses, procedures, and treatments from all hospitals in Denmark. Established in 1977, the DNRP uses the International Classification of Diseases diagnosis codes. Prior to 1994, the ICD-8 was used; from 1994 and onwards, the ICD-10 version has been used. Patients can be identified by the specific ICD diagnosis code, by alternative identification methods (eg, predefined clinical algorithms based on a constellation of diagnoses and/or procedures), or in combination with data on medication use from the Danish Prescription Registry.Citation45 Further, when linked to the DNRP for inhospital treatment data and/or to the Danish Prescription Registry for redeemed prescriptions, a genetic cohort can potentially be used in comparative effectiveness research to provide evidence on the effectiveness, benefits, and harms of different treatments. One limitation of the DNRP with regard to identifying patients with genetic conditions is that some genetic disorders are not registered with a specific ICD-10 code, but rather with a general ICD-10 code, eg, DZ80.0 (family history of gastrointestinal cancer) or the unspecific ICD-10 Z848 (family history of other specified conditions). This registration practice is used by geneticists to protect patient privacy. Further, family history is likely to be under-reported in the DNRP. Therefore, it is crucial that clinical geneticists or other experts are consulted about the coding/registration practices for a particular genetic condition. For a number of genetic disorders, querying the DNRP should be supplemented with accessing data from the departments of clinical genetics or other specialized centers (see ).
The National Pathology RegistryCitation44 (www.patobank.dk) is a registry of histological examinations reported by pathologists. Data have been collected since 1997. Variables include (but are not limited to) histological specimens, procedures, and diagnoses (primarily topography and morphology, but other features may also be registered). Diagnoses are coded using the International Systemized Nomenclature of Medicine. The National Pathology Registry is a potential source of data for conditions diagnosed by histopathological examination, such as cancers and genodermatoses.
The Civil Registration System is an administrative registry that provides up-to-date information on age, gender, region of residence, vital status, parent/child relationships, and other variables, including the CPR number.Citation5,Citation41 The Civil Registration System has data on every person who has legally resided in Denmark since April 1968. The CPR number enables linkage of data from multiple registries, and thereby the collection of data at the individual and familial levels, unambiguously and without double-counting. Data in the Civil Registration System is virtually complete, eg, vital status is updated electronically on a daily basis.
In addition to the previously mentioned data sources (ie, the Civil Registration System and the Danish Medical Birth Registry), church book archives are also potential sources for identifying relatives and pedigrees. Finally, Statistics Denmark (www.dst.dk), which includes StatBank Denmark (www.statbank.dk), contains descriptive statistical information on the Danish society, including data on household/families and children.
Danish research setting
Access to Danish registry data and data linkage requires authorization by the Danish Data Protection Agency (Datatilsynet) and in some cases, additional authorization from the Danish Health and Medicines Authority, typically when medical charts are to be accessed,Citation46 and/or authorization from the National Committee on Health Research Ethics (Den Nationale Videnskabsetiske Komité) if biological specimens are to be used or if living persons are to participate in clinical studies. The Danish privacy laws on the use of personal data are stipulated in The Act on the Processing of Personal Data (Act Number 429; May 31, 2000).Citation47,Citation48
As a general rule, the results of statistical analyses may be published or publicly released in an aggregated form such that individuals remain nonidentifiable. Otherwise, public release of any individual data (ie, data that can lead to identification of an individual) requires explicit consent from that person. For further information on Danish privacy laws and online application for authorization to access registry data, visit the Danish Data Protection Agency homepage (http://www.datatilsynet.dk).
Once authorization for data access has been granted by the Danish Data Protection Agency, data can be obtained after approval and release by the individual registry administrators. For the national registries housed at the Danish State Serum Institute (Statens Serums Institut), an application for data release must be filed at the research service unit of this institute (Forskerservice, at http://www.ssi.dk/Sundhedsdataogit/Forskerservice.aspx).
Scientists in other European Union countries are subject to the same guidelines and procedures for data access as scientists in Denmark (described above). Release of registry data to non-European Union countries may require further evaluation by the Danish Data Protection Agency in order to ensure sufficient data security and handling in accordance with Danish law. Detailed information on the application procedure for data access for researchers outside Denmark can be found at the Danish Data Protection Agency homepage (http://www.datatilsynet.dk/erhverv/tredjelande/overfoersel-til-tredjelande/).
Conclusion
There is a wealth of existing medical data sources on genetic diseases in Denmark. The ability to link and collect data at both the individual and familial levels allows for rapid identification of relevant study subjects/families and the collection of comprehensive medical histories spanning from time of birth to death. The Danish collection of medical registries is a valuable resource for genetic epidemiology and comparative effectiveness research, both in and outside of Denmark.
Acknowledgments
This study received funding from the Department of Clinical Epidemiology Research Foundation. Our sincere thanks are extended to the following people for their help in collecting information for this project: Jette Ørsted (Department of Clinical Genetics, Aarhus University Hospital), Sven Asger Sørensen (Institute for Cellular and Molecular Genetics, Panum Institute, Copenhagen University), Thomas Rosenberg (The National Eye Clinic, Kennedy Center, Copenhagen), Inge Bernstein (HNPCC-registry Clinical Research Center, Hvidovre Hospital), Hanne Buciek Hove (Department of Clinical Genetics, Rigshospitalet), Oluf Schiøtz (Department of Pediatrics, Aarhus University Hospital), Hanne Vebert Olesen (Department of Pediatrics, Aarhus University Hospital), Susanne Møller (Danish Breast Cancer Cooperative Group), Niels Jespersen (Department of Gastric Surgery, Hvidovre Hospital), Søs Marie Luise Bisgaard (Cellular and Molecular Medicine, Panum Institute, Copenhagen University), Marie Louise Mølgaard Binderup (Cellular and Molecular Medicine, Panum Institute, Copenhagen University), Charlotte Kvist Lautrup (Department of Clinical Epidemiology, Aarhus University Hospital), Allan Meldgaard Lund (Clinic for Rare Handicaps, Rigshospitalet), Ann Tabor (Center for Fetal Medicine and Pregnancy, Department of Obstetrics, Rigshospitalet), Mette Sommerlund (Department of Dermatology, Aarhus University Hospital), Anette Bygum (Department of Dermatology, Odense University Hospital), Stense Farholt (Centre for Rare Diseases and Department of Pediatrics, Aarhus University Hospital), Hans Gjørup (Centre for Oral Health in Rare Diseases, Aarhus University Hospital), Anne-Marie Gerdes (Department of Clinical Genetics, and the Clinic for Rare Handicaps, Rigshospitalet, Copenhagen), Karen Brøndum-Nielsen (Kennedy Center, Copenhagen), Michael B. Petersen (Department of Clinical Genetics, Aalborg University Hospital), Jette Daugaard-Jensen (Centre for Rare Oral Diseases, Odontologisk Videncenter, Copenhagen), Lotte Nylandsted Krogh (Department of Clinical Genetics, Odense University Hospital), Anders Bojesen (Department of Clinical Genetics, Vejle Hospital), Jens Michael Hertz (Department of Clinical Genetics, Odense University Hospital) and Camilla Daasnes (Data Protection Agency).
Disclosure
The authors declare no conflicts of interest in this work.
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