Inclusion Criteria:
1. Confirmed diagnosis of Familial Mediterranean Fever (FMF) based on new diagnostic criteria of the Eurofever/PRINTO expert group (2019)
2. Male and female participants aged ≥ 5 and \< 18 years at the time of signing Informed Consent Form (ICF) and Visit 1, respectively:
2.1. In Kingdom of Saudi Arabia, the upper age limit is 14 years (i.e. the participants should be between ≥ 5 and ≤ 14 years old)
2.2. In other countries, the upper age limit is 18 years (i.e. the participants should be between ≥ 5 and \< 18 years old)
3. Availability of a voluntarily signed and dated ICF for participation in this study: the informed consent of the parent or legal representative and the consent of the child
4. Availability of one of the documented data listed below (at the time of the start of screening) (records of medical examinations/consultations including those done by the investigator, hospital discharges) confirming:
4.1. colchicine resistance at the maximum tolerated therapeutic dose (depending on age and weight) confirmed by the persistence of at least one attack of the disease per month on average, despite the indicated therapy for at least the last 3 months before the start of screening. Colchicine administration will be continued at stable dose if it is not associated with unacceptable adverse drug reactions
4.2. intolerance to therapeutic or subtherapeutic doses of colchicine (presence of unacceptable adverse drug reactions). The dose of colchicine should be stable for at least 5 days before the participant is enrolled (before screening)
5. Ability of the participant and the parent (legal representative) and willingness, in the reasoned opinion of the investigator, to visit the study site during all scheduled visits, to perform the study-related procedures and comply with the Protocol requirements including consent to undergo subcutaneous injections by qualified personnel of the site
6. One active attack with a duration of no more than 2 days (48 hours) at the time of Visit 1 defined as the development of both clinical and serological signs of an attack including:
1. Physician's Global Assessment (PGA) score ≥ 2 suggesting "mild", "moderate", or "severe" disease activity (i.e. clinical signs)
2. C-reactive protein (CRP) level \> 10 mg/L (i.e. serological signs)
7. The Russian Federation, the Hashemite Kingdom of Jordan and the Republic of Turkey: Consent of female adolescents, after menarche, to use highly effective contraceptives throughout the study, starting from the screening (signing ICF) and for at least 8 weeks after completion (termination) of the study therapy; as well as the presence of a negative pregnancy test (serum test for chorionic human gonadotropin (HCG)) OR Consent of sexually active male adolescents to use highly effective contraceptives throughout the study, starting from the screening (signing ICF) and for at least 8 weeks after completion (termination) of the study therapy
Exclusion Criteria:
1. Hypersensitivity to GFC and/or its components/excipients
2. Administration of live (attenuated) vaccine less than 3 months prior to Visit 1 (treatment period initiation) and/or necessity to use such vaccine within 3 months after GFC discontinuation
3. Conditions or signs which, according to the investigator, suggest impaired (reduced) immune response and/or significantly increase the risk of immunomodulating therapy including (but not limited to):
3.1. any acute or chronic active infection at the time of screening, an infection requiring antimicrobial therapy within 4 weeks prior to screening, or a history of serious, opportunistic, or frequently recurring infection within 6 months prior to screening
3.2. presence of infection caused by the human immunodeficiency virus (HIV), hepatitis B virus or hepatitis C virus
4. History of active or latent tuberculosis (TB) or existing risk factors or signs suggestive of active or latent M. tuberculosis including (not limited to) the following:
4.1. living or working in specific conditions that increase the risk of contact with participants with TB, such as residential care, places of deprivation of liberty, communities of persons without a special place of residence, etc. during the last year before the start of the treatment period
4.2. close contact, i.e. living at the same premises (at home or in another enclosed environment) for a prolonged period of time (several days or weeks, rather than minutes or hours) with a person with active pulmonary TB during the last year before the start of the treatment period
4.3. results of examinations indicating active or latent infection with M. tuberculosis: positive QuantiFERON-TB / T-SPOT.TB test at screening; chest Xray/CT findings confirming pulmonary TB during screening
5. Any other relevant concomitant diseases or conditions that, in the Investigator's judgment, may affect the participant's participation or well-being in the study and/or interfere with the assessment of study results
6. History of organ transplantation or necessity in transplantation at the screening onset
7. Surgical intervention within 8 weeks prior to the screening or planned for the period of participation in the study, which, in the investigator's opinion, agreed with the Sponsor, will generate an unacceptable risk for the participant
8. Any existing malignant neoplasm during the screening period or within 5 years prior to screening, including blood and lymphatic neoplasm, except non-metastatic basal cell and squamous cell skin cancer after complete resection or carcinoma in situ of any type after complete resection
9. Pregnancy or breast-feeding
10. History of alcohol or psychoactive substances abuse, according to the investigator's evaluation
11. Previous administration of:
* rilonacept - less than 6 weeks prior to Day 0 of the study
* canakinumab - less than 12 weeks prior to Day 0 of the study
* anakinra - less than 72 hours prior to Day 0 of the study
* rituximab - less than 24 weeks before day 0
* tumor necrosis factor (TNF) inhibitors, IL-6 inhibitors and other biological medications with an immunosuppressive mechanism of action - less than 6 weeks or 5 half-lives (whichever is longer) before study day 0
* immunosuppressants (azathioprine, leflunomide, dapsone, cyclosporine, mycophenolate mofetil, tacrolimus, sirolimus, mercaptopurine, methotrexate, etc.) - less than 4 weeks or 5 elimination half-lives (whichever is longer) before study day 0. In case of leflunomide administration complete elimination course using cholestyramine should be documented
* intravenous (IV) immunoglobulin (Ig) - less than 8 weeks before day 0;
* intravenous administration of glucocorticoids - less than 1 week (from the end of therapy) to study day 0
* intramuscular, intra-articular or periarticular administration of glucocorticoids - less than 4 weeks before day 0
* systemic oral glucocorticoid therapy at doses \> 0.2 mg/kg/day of prednisolone equivalent on day 0
* changes in the dose/treatment regimen of oral glucocorticoids during the 4 weeks prior to the screening
12. Any of the deviations in the laboratory tests below:
* neutrophil count \< 1.5×10\^9/L (\< 1500/mm\^3)
* white blood cell (WBC) count \< 3×10\^9/L (\< 3000/mm\^3)
* platelet count \< 100×10\^9/L (\< 100 000/mm\^3 or \< 100 000×10\^6/L)
* ALT and/or AST ≥ 2.0 × upper limit of normal (ULN); if ALT and/or AST is ≥ 2 × ULN but \< 3 × ULN at the screening, retest is allowed
* bilirubin \> 1.5 x ULN (except for confirmed Gilbert's disease)
13. Concomitant participation in other clinical studies at the screening onset or administration of any unauthorized (investigational) medications less than 4 weeks or 5 half-life periods (whichever is longer) before Visit 1 (treatment initiation)
14. Prior participation in this clinical study in case of at least one GFC dose
15. Severe renal failure: Glomerular filtration rate (GFR) calculated by Schwartz formula is \< 45 mL/min/1.73 m\^2
