Estimation of the number of patients with mitochondrial diseases: A descriptive study using a nationwide database in Japan.

BACKGROUND To provide a better healthcare system for patients with mitochondrial diseases, it is important to understand the basic epidemiology of these conditions, including the number of patients affected. However, little information about them has appeared in Japan to date. METHODS To gather data of patients with mitochondrial diseases, we estimated the number of patients with mitochondrial diseases from April 2018 to March 2019 using a national Japanese health care claims database, the NDB (National Database). Further, we calculated the prevalence of patients, and sex ratio, age class, and geographical distribution. RESULTS From April 2018 to March 2019, the number of patients with mitochondrial diseases was 3,629, and the prevalence was 2.9 per 100,000 general population (95% CI, 2.8-3). The ratio of females and males was 53 to 47, and the most frequent age class was 40-49 years old. Tokyo had the greatest number of patients with mitochondrial diseases, at 477, whereas Yamanashi had the fewest, at 13. Kagoshima had the highest prevalence of patients with mitochondrial diseases, 8.4 (95% CI, 7.1-10) per 100,000 population, whereas Yamanashi had the lowest, 1.6 (95% CI, 0.8-2.7). CONCLUSION The number of patients with mitochondrial diseases estimated by this study, 3,269, was more than double that indicated by the Japanese government. This result may imply that about half of all patients are overlooked for reasons such as low severity of illness, suggesting that the Japanese healthcare system needs to provide additional support for these patients.