Epidemiology of Mucopolysaccharidosis Type II According to the Register of the Russian Federation.

Objective: The study aimed to evaluate the epidemiological, clinical, and molecular data of mucopolysaccharidosis type II (MPS II) patients and their outcomes using the national registry of patients in the Russian Federation (RF). Materials and Methods: In the retrospective cohort study, the authors included data from the Russian national registry of MPS II. Results: The prevalence of MPS II in RF is 0.62 per 100 000 live births or 0.09 per 100 000 population with the majority of patients in the Central (n = 36) and the Volga Federal District (n = 35). Males were 157 (99.4%), positive MPS II family history had 47 (29.7%) patients. The median age of the first symptoms was 1.8 (0.8-2.6) years, ranging from 0.1 to 19 years, and the age of diagnosis was 4.0 (2.5; 5.9) years, ranging from 0.1 to 38.9 years. A genetic study was available for the analysis in 116 (73.4%) patients. Single nucleotide variants in the IDS gene were found in 98/116 (84.5%) patients, and 18 further patients (15.5%) had gross rearrangements. About 59/98 (60.2%) patients had missense, 15/98 (15.3%) had frame-shift variants, 12/98 (12.2%) had splice site, and 11/98 (11.2%) had nonsense variants. One (1.0%) patient out of 98 patients had a small deletion. Pathogenic, likely pathogenic variants, and variants with uncertain significance were found in 54 (55.1%), 36 (36.7%), and 8 (8.2%) patients, respectively. About 138 (87.3%) patients received enzyme replacement therapy. Conclusion: The prevalence of MPS II in the RF is higher than that in some European countries and closer to the Asian population. The registry is a convenient tool for disease epidemiology and monitoring.