Periodontitis and Inflammation in Children With Down Syndrome/Trisomy 21: Study on Biological Samples

Inclusion Criteria: Common to all groups: * Age: 3 to 12 * Patient affiliated to a social security program, beneficiary not covered by the AME. * Legal representatives who speak and understand French well enough to be able to read and understand the study information. * Legal representatives giving written consent for their child's participation in the study. Specific: Case Group: * Trisomy 21 patient with gingival inflammation (subgroup 1) * Trisomy 21 patient with healthy gingiva on intact periodontium with no history of periodontitis (subgroup 2) Control Group: child meeting one of these criteria: * Patient with psychomotor retardation with no known repercussions on the orofacial sphere or immunity, presenting gingival inflammation (subgroup 1) * Patients with psychomotor retardation and no known repercussions on orofacial health or immunity, presenting gingival health on intact periodontium with no history of gingival inflammation (subgroup 2). * Patients with no known general pathology and gingival inflammation (subgroup 3) * Patients with no known general pathology and healthy gingiva on intact periodontium with no history of gingival inflammation (subgroup 4) Exclusion Criteria: Common to all groups: * Patient having received antibiotic prophylaxis, antibiotic therapy or anti-inflammatory treatment in the 3 months prior to inclusion * Patient included in another interventional research protocol or in a period of exclusion. * Patient on AME * Patients with a contraindication to the use of MEOPA: * Patients requiring pure oxygen ventilation * Intracranial hypertension * Unevaluated head trauma * New-onset, unexplained neurological abnormalities * Pneumothorax * Emphysema bubbles * Gas embolism * Diving accident * Abdominal gas distension, occlusion * Patient recently treated with ophthalmic gas (SF6, C3F8, C2F6) * Known, unsubstituted vitamin B12 deficiency Specific to Trisomy 21 group: \- Patient with no genetic diagnosis