The recent surge in twin births across India, driven by assisted reproductive technologies and delayed maternal age, presents an unprecedented scientific opportunity that we are systematically missing. While countries like the United Kingdom (Verdi et al., Reference Verdi, Abbasian, Bowyer, Lachance, Yarand, Christofidou, Mangino, Menni, Bell, Falchi, Small, Williams, Hammond, Hart, Spector and Steves2019), Australia (Hopper, Reference Hopper2002), and the Nordic nations (Nilsen et al., Reference Nilsen, Knudsen, Gervin, Brandt, Røysamb, Tambs, Ørstavik, Lyle, Reichborn-Kjennerud, Magnus and Harris2013) have leveraged twin registries to revolutionize our understanding of disease heritability, gene-environment interactions, and treatment responses, India — with its 1.4 billion population and remarkable genetic diversity — remains conspicuously absent from this vital research arena (Dhar et al., Reference Dhar, Rana, Srivastava, Nayek, Sharma, Kaur, Kalari, Singh and Karmakar2022).

Twin studies have fundamentally shaped modern medicine. From establishing the heritability of cardiovascular disease (Osler et al., Reference Osler, Villumsen, Jørgensen, Hjelmborg, Christensen and Wium-Andersen2022) to unravelling the complex etiology of autism spectrum disorders (Lundström et al., Reference Lundström, Reichenberg, Melke, Råstam, Kerekes, Lichtenstein, Gillberg and Anckarsäter2015), twins provide nature’s perfect control experiment. Yet India, which produces an estimated 30,000−40,000 twin pairs annually, has no systematic mechanism to harness this invaluable resource. The case for establishing a National Twin Registry in India is compelling on multiple fronts. First, India’s extraordinary genetic heterogeneity (Department of Biotechnology, Government of India, 2022), with over 4600 distinct population groups, offers unparalleled opportunities to study gene-environment interactions across diverse ancestries. Conditions ranging from type 2 diabetes to tuberculosis show marked variation across Indian populations, and twin studies could illuminate whether these differences stem from genetic susceptibility, environmental exposures, or their interplay. Second, India’s rapidly evolving environmental landscape — from urbanization and dietary transitions to pollution exposure — creates natural experiments in real-time. Discordant twin pairs, where one twin develops disease, and the other does not, despite shared genetics, can reveal critical environmental triggers and protective factors. This is particularly relevant for India’s mounting burden of noncommunicable diseases, where prevention strategies remain frustratingly imprecise. Third, the rise of ART in India (Malhotra et al., Reference Malhotra, Shah, Pai, Pai and Bankar2013) has increased dizygotic twinning rates significantly, providing larger cohorts for research while simultaneously raising important questions about long-term health outcomes in ART-conceived children that only longitudinal twin studies can adequately address.

The infrastructure requirements, while substantial, are achievable. A federated model, linking existing birth registries with opt-in research participation, could leverage India’s digital health initiatives like the Ayushman Bharat Digital Mission (ABDM; Lahariya, Reference Lahariya2018). Starting with pilot registries in states with robust health infrastructure in the Southern Indian States — Kerala, Tamil Nadu, or Karnataka — would allow iterative refinement before national scale-up. Critics may argue that India has more pressing health priorities. This represents false dichotomy thinking. A twin registry requires modest ongoing investment while generating insights applicable across the disease spectrum (Dhar et al., Reference Dhar, Rana, Srivastava, Nayek, Sharma, Kaur, Kalari, Singh and Karmakar2022) — from infectious diseases to cancer, mental health to ageing. The return on investment, measured in prevented disease burden and more targeted interventions, would be substantial. International collaborations could accelerate development. Partnerships with established registries such as TwinsUK or the Australian Twin Registry would provide technical expertise, while India’s scale and diversity would enrich global research. Data sovereignty concerns can be addressed through robust governance frameworks, ensuring that Indian data primarily benefits Indian health priorities. Perhaps most importantly, a twin registry would catalyse India’s transition from being a research subject pool to a research leader. Indian investigators could drive discovery rather than merely participating in studies as a sample stock for the world. The time for a National Twin Registry in India is now (Dhar et al., Reference Dhar, Rana, Srivastava, Nayek, Sharma, Kaur, Kalari, Singh and Karmakar2022). As precision medicine promises increasingly personalized interventions, understanding the interplay between our genes and environments becomes critical (Guo, Reference Guo2000). India cannot afford to remain a bystander in this revolution, particularly when it possesses one of the world’s most valuable — and currently untapped — research resources: its twins.