Ethnic heterogeneity of juvenile arthritis in the Republic of Sakha (Yakutia) related to a high human leukocyte antigen B27 frequency

Table 1 The incidence of juvenile idiopathic arthritis in the Republic of Sakha (Yakutia)

Year	Number of JIA cases	Incidence of JIA per 100000 children
2016	14	5.3
2017	26	9.8
2018	24	9.1
2019	22	8.3
2020	18	6.8
2021	31	11.7
2022	26	9.8
2023	41	15.5

JIA: Juvenile idiopathic arthritis.

Table 2 Prevalence of juvenile idiopathic arthritis in the Republic of Sakha (Yakutia) in 2023, n (%)

The prevalence of JIA1	Total patients [n (%)/n]1	Sakha (n = 168) [n (%)/n]1	Russians (n = 49) [n (%)/n]1	P value
Population	266/293	596 (57.0)/152	622 (43.0)/70
Living area
Urban	123 (54.7)/73.6	87 (51.8)/139.3	30 (61.2)/45.4	0.258
Rural	102 (45.3)/102.8	81 (48.2)/89.8	19 (38.8)/406.2
Gender
Boys	118 (52.4)/86.8	83 (49.4)/106.6	19 (38.8)/52.7	0.198
Girls	107 (47.6)/81.9	85 (50.6)/113.6	30 (61.2)/86.6
JIA categories2
Systemic arthritis	8 (3.5)/3.0	3 (1.8)/2.0	4 (8.1)/5.7	0.00005
Oligoarthritis	76 (33.8)/28.5	47 (28.0)/30.8	26 (53.0)/36.8
Polyarthritis, RF (-)	33 (14.7)/12.4	25 (14.9)/16.4	8 (16.3)/11.3
Polyarthritis, RF (+)	2 (0.9)/0.8	2 (1.2)/1.3	0 (0.0)/0
Enthesitis-related arthritis	99 (44.0)/37.2	86 (51.1)/56.4	9 (18.4)/12.7
Psoriatic arthritis	7 (3.1)/2.6	5 (3.0)/3.3	2 (4.1)/2.8

¹Per 100000 children.

²According to the International League of Associations for Rheumatology classification[2].

JIA: Juvenile idiopathic arthritis; RF: Rheumatoid factor.

Table 3 Clinical, demographic, and laboratory characteristics of children with juvenile idiopathic arthritis in the Republic of Sakha (Yakutia), n (%)

Parameters	n = 225
Gender: Boys [n (%)]/girls [n (%)]	107 (47.6%, 95%CI: 41.1-54.1)/118 (52.4%, 95%CI: 45.9-58.9])
Age at JIA onset, medians (25%, 75%)	9 (5, 12)
Family history of immune-inflammatory diseases	60 (26.7%, 95%CI: 21.3-32.8)
Arthritis in the close relatives	46 (20.4%, 95%CI: 15.7-26.2)
JIA categories, International League of Antirheumatic Associations
Systemic arthritis	8 (3.5%, 95%CI: 1.8-6.9)
Oligoarthritis	76 (33.8%, 95%CI: 27.9-40.2)
Polyarthritis, RF (-)	33 (14.7%, 95%CI: 10.6-19.9)
Polyarthritis, RF (+)	2 (0.9%, 95%CI: 0.2-3.2)
Enthesitis-associated arthritis	99 (44.0%, 95%CI: 37.7-50.5)
Psoriatic arthritis	7 (3.1%, 95%CI: 1.5-6.3)
Active joints, medians (25%, 75%)	4 (2, 10)
Sacroiliitis	43 (19.1%, 95%CI: 14.5-24.8)
Enthesites	34 (15.1%, 95%CI: 11.0-20.4)
Uveitis	23 (10.2%, 95%CI: 6.9-14.9)
Psoriasis	7 (3.1%, 95%CI: 1.5-6.3)
Antinuclear antibodies-positivity	30/45 (66.7%, 95%CI: 52.1-78.6)
Human leukocyte antigen-B27 positivity	87/220 (39.6%, 95%CI: 33.3-46.1)
RF-positivity	1 (0.4%, 95%CI: 0.1-2.5)

JIA: Juvenile idiopathic arthritis; RF: Rheumatoid factor.

Table 4 Therapy of juvenile idiopathic arthritis in children of the Republic of Sakha (Yakutia), n (%)

Therapy	Results (n = 225)
Nonsteroidal antirheumatic drugs	225 (100)
Glucocorticosteroids
Not received	180 (80.0)
Intravenous	11 (4.8)
Oral	5 (2.2)
Intra-articular	22 (9.7)
Sulfasalazine	8 (3.6)
Methotrexate	205 (91.5)
Early methotrexate withdrawal	29/205 (14.1)
Leflunomide	1 (0.4)
Cyclosporine A	5 (2.2)
Patients, treated with biologics	91 (40.4)
The first-line biological drugs
Etanercept	60/91 (65.9)
Adalimumab	21/91 (23.1)
Tocilizumab	7/91 (7.7)
Secukinumab	2/91 (2.2)
Abatacept	1/91 (1.1)
Time to the first biologic, medians (25%, 75%) (months)	6 (3, 18)
Remission on the first biologic	34/86 (39.5)
Time to remission on the first biologic, medians (25%, 75%) (months)	8.5 (6, 24)
De-novo uveitis on etanercept	4/60 (6.7)
Patients, treated with second-line biologic	12/91 (13.8)
The second-line biological drugs
Etanercept	1 (8.3)
Adalimumab	5 (41.7)
Tocilizumab	1 (8.3)
Secukinumab	2 (16.7)
Abatacept	1 (8.3)
Upadacitinib	2 (16.7)
Time to the second biologic, medians (25%, 75%) (months)	24 (2, 38)
Patients with remission on the second biologic	5/11 (45.5)
Time to remission on the second biologic, medians (25%, 75%) (months)	6 (6, 6)