The Population-Based Hungarian Twin Registry: Current Register Data, Researches and Linkages

The Hungarian Twin Registry (HTR) has operated as a population-based registry since 2021, following its establishment at Semmelweis University in Budapest. In recent years, the HTR infrastructure has been substantially expanded, including blood storage facilities, information technology systems, a phone bank and voicemail system, and administrative resources. Adult twins (aged ≥18 years) and relatives (parents, foster parents, or caregivers) of twins under 18 years of age can register via the registry's website or by voicemail following a nationwide identification and notification process. The registration questionnaire consists of eight sections covering sociodemographic and anthropometric characteristics, smoking habits, and medical history, including diseases, surgeries, and therapies. By December 20, 2025, a total of 12,676 twin individuals and their parents or guardians had registered, including 7244 adult twins and 5432 parents or guardians of minors. Based on self-reported data, 44.1% of registered adult twins were monozygotic (MZ) and 55.9% dizygotic (DZ), while among registered children 23.5% were MZ and 76.5% DZ. Of the registered adult twins, 68.4% were female. The HTR offers substantial potential for linkage with national health databases, enabling enrichment of phenotypic and outcome data without additional participant burden. In particular, linkage with the Hungarian National Cancer Registry and other health-related databases is feasible under appropriate ethical approval and data protection procedures and may support long-term follow-up and disease-specific analyses. The article also summarizes current research projects conducted within the HTR, which has become the largest population-based twin registry in Central and Eastern Europe based on the number of registrations.