Clozapine-related Immunodeficiency in Parkinsons Disease

Inclusion Criteria: * Patient ≥ 18 years old with Parkinson's disease according to MDS 2015 criteria * Psychotic symptoms requiring treatment with Clozapine * Patients with initially a normal leukocyte count (number of white blood cells ≥ 3500/mm3 \[3.5 x 109/l\] and an absolute neutrophil count PNN ≥ 2000/mm3 \[2 x 109/l\]) * patients in whom the number of white blood cells (WBC) and the absolute number of neutrophils (PNN) may be determined regularly at the following intervals: once a week during the first 18 weeks of treatment and, thereafter, at least every 4 weeks for the duration of the treatment. This monitoring must be continued throughout the treatment and for 4 weeks who follow the complete cessation of CLOZAPINE * Informed and written consent. * Affiliation to a social security system Exclusion Criteria: * Patients with a contraindication to the use of Clozapine according to the summary of product characteristics (SPC) * Hypersensitivity to the active substance or to any of the excipients. * Patients who cannot receive regular blood tests. * History of granulopenia or toxic or idiosyncratic agranulocytosis (unless it results from previous chemotherapy). * History of agranulocytosis induced by CLOZAPINE * Treatment with CLOZAPINE should not be started at the same time as substances known to have a high potential for inducing agranulocytosis; The concomitant administration of depot antipsychotics is not recommended. * Functional bone marrow failure. * Uncontrolled epilepsy. * Alcoholic or induced psychosis, drug intoxication, comatose states. * Circulatory collapse and / or CNS depression regardless of the aetiology. * Severe renal or cardiac disorders (eg: myocarditis). * Active liver disease with nausea, anorexia or jaundice; progressive liver disease, liver failure. * Paralytic ileus. * Patient with another potential cause of immunosuppression * Immunosuppressive or immune modulatory treatment active or stopped for less than 5 years * Anti-epileptic treatment active or stopped for less than 5 years * Chemotherapy active or stopped for less than 5 years * Solid or hematologic cancer active or treated for less than 5 years * Human immunodeficiency virus infection * Already known constitutional immune deficiency * Nephrotic syndrome * Protein-losing enteropathy * A history of radiotherapy * Long-term use of corticosteroids * Patient with potentially major cognitive disorders defined by a MoCA score less than or equal to 23 * Pregnant or breastfeeding women * Patient under guardianship/curatorship or deprived of liberty