What is Nan-Byo?


Image courtesy of Riri Adachi

Nan-Byo literally means ‘difficult+illness’ in Japanese. The term was first coined in 1972 by the Japanese Ministry of Labour, Health and Welfare, as a number of significant, but relatively rare, health issues in came to public attention, prompting fundamental reform of the national health system for these conditions1. Central to the government policy was to support quality of life with dignity in society for Nan-Byo patients4.

The Ministry’s definition for Nan-Byo includes two elements. The first is that the disease is from an unidentifiable cause, without a clearly established treatment, and has a considerably high risk of disability. The second element is that these diseases tend to be chronic and place a significant care burden on the family3.

For patients, the difficult journey through the health system begins with diagnosis. ‘Diagnosis’ may often be a non-diagnosis, or protracted period until diagnosis, as little information may exist about the condition, making it difficult for medical practitioners to identify. A patient is likely to need to be referred to specialised medical testing, which in Japan’s healthcare system, can include the latest options of genomic testing.

Following the diagnosis, the patient next faces the difficulties of finding appropriate treatment as the condition may be quite complex and require tailoring a combination of specialised treatments.

The intractable nature of these diseases tends to be matched with the protracted nature of the condition. For this reason, the term Nan-Byo stands out amongst the international dialect of rare diseases as it captures the notion that carers and families also suffer with the patient. Families experience the difficulties of providing protracted, often lifelong, patient care. Families face a considerable financial and mental burden as they incur significant expenses in caring for the patient and often feel socially isolated.

In 2014, consideration of Nan-Byo patients moved from the Disability Act to a newly established Nan-Byo Act, which aimed to streamline and improve the support for identified patients. This also refined the definition of ‘rare disease’ to affect less than 0.15 per cent of the population, although this is flexible and some exceptions may apply. This notion of ‘prevalence’ is important as brings the Japanese definition into line with other international definitions, which tend to have, on average, 40 cases per 100,000 individuals5.


  1. Adachi, T., Kawamura, K., Furusawa, Y., Nishizaki, Y., Imanishi, N., et al. Japan’s initiative on rare and undiagnosed diseases (IRUD): towards an end to the diagnostic odyssey. European Journal of Human Genetics 25, 1025–1028 (2017). doi:10.1038/ejhg.2017.106 | article
  2. Dawkins, H.J.S., Draghia-Akli, R., Lasko, P., Lau., LP.L., Jonker, A.H., et al. Progress in Rare Diseases Research 2010–2016: An IRDiRC Perspective. Clinical Translational Science 11, 11–20 (2018). doi:10.1111/cts.12501 | article
  3. Tang, W. and Makuuchi, M. Intractable and rare diseases research. Intractable & Rare Diseases Research 1, 1-2 (2012). doi: 10.5582/irdr.2012.v1.1.1 | article
  4. Ito, T. Patient groups’ advocacy activity and Nanbyo Act (The iatric services to pateints suffering from intractable disease). Iryo To Shakai, Special Issue: Clinical Trials and Clinical Researches 28, 27-36 (2018). doi:10.4091/iken.29.027 | article
  5. Richter, T., Nestler-Parr, S., Babela, R., Khan, Z., Tesoro, T. et al. Rare disease terminology and defnintions – a systematic global review: Report of the ISPOR Rare Diseases Special Interest Group. Value in Health 18, 906-914. (2015). doi: 10.1016/j.jval.2015.05.008 | article