Could a hyperactive immune system fuel PMDD? a new study investigates

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: Participants must: * Have been assigned female sex at birth (AFAB), with ovaries * Be aged between 18-42 years (inclusive) * Be able to provide written informed consent * Be premenopausal * Have regular menstrual cycles (24-35 days; 5-8 menstrual cycles within the previous 6 months) * Have a body mass index (BMI) between 18 and 30 kg/m². * Have access to a computer, tablet or smartphone with an internet connection. * Be registered with a UK General Practitioner (GP) and consent to the study team contacting their GP if clinically indicated. PMDD group only - Participants must additionally: • Meet DSM-5 diagnostic criteria for Premenstrual Dysphoric Disorder (PMDD), confirmed through prospective symptom ratings and the study diagnostic assessment. Healthy control group only - Participants must additionally: * Have no current or previous diagnosis of PMDD. * Report no clinically significant premenstrual symptoms on prospective symptom ratings. * Have no lifetime psychiatric illness * Meet all other study eligibility criteria. Exclusion Criteria: Participants will be excluded if they: * Have a lifetime history of a psychotic disorder (including schizophrenia, schizoaffective disorder or major depressive disorder with psychotic features) or bipolar disorder (past or present) * Meet criteria for any other current major psychiatric disorder that would interfere with study participation, as determined by the MINI International Neuropsychiatric Interview. * Have a history of drug or alcohol dependence within the previous 12 months. * Have a diagnosed intellectual disability, pervasive developmental disorder or significant neurological disorder (e.g. Alzheimer's disease, epilepsy or Parkinson's disease). * Are currently pregnant or breastfeeding, or are planning pregnancy during the study period. * Have an acute infection, autoimmune disorder, or regularly use anti-inflammatory or antibiotic medication that could influence immune biomarkers. * Have a current or previous gynaecological condition (e.g. endometriosis or polycystic ovary syndrome) or have undergone gynaecological surgery within the previous 12 months. * Have used hormonal contraception or other steroid hormone treatment within the previous 6 months (except emergency levonorgestrel contraception or temporary hormone treatment for oocyte cryopreservation that has not affected menstrual cycle regularity). * Have a significant medical condition that may affect study outcomes (e.g. cancer, inflammatory disease, liver disease, kidney disease or Crohn's disease). * Are currently participating in a Clinical Trial of an Investigational Medicinal Product (CTIMP). Eligibility following recent participation in a CTIMP will be considered on a case-by-case basis. * Are assessed as presenting an immediate or high risk of suicide requiring urgent clinical intervention. Suicidal ideation alone is not an exclusion criterion because it is recognised as a feature of PMDD; however, participants identified as being at significant risk will be excluded and referred to appropriate clinical services.