Study to Evaluate the Effect of Lixisenatide in Patient With Parkinson's Disease

Inclusion Criteria: * Patients with PD according to UKPDSBB criteria (male or female). * Patient with a Hoehn and Yahr Stage \<3 in the ON condition. * Patients aged from 40 to 75 years old. * Early-stage PD patients: diagnosis of PD for less than 3 years, without dyskinesia and motor fluctuations. * Patients treated with an "optimized" stable dopaminergic medication regimen (dopamine agonist and/or L-dopa and/or MAOB inhibitor) for at least 1 month before baseline. * Patients expected to remain on stable doses of antiparkinsonian medications for at least the first 6 months of the study and preferably for the 12 months of follow-up. * Patients (or caregiver) able to self-administer lixisenatide injection. * Patients with health insurance. * Patients who signed the written informed consent form. Exclusion Criteria: * Patients suffering from other parkinsonian syndromes other than PD. * Patients expected not to be able to remain on stable doses of symptomatic antiparkinsonian medications for at least 6-month. * Patients with a Body Mass Index \< 18.5 * Patients suffering from type 1 or type 2 diabetes. * Malnutrition as assessed clinically by the investigator or any sub-investigator and by Mini Nutritional Assessment Short Form (MNA-SF) score \<12 (the judgement of the investigator prevails over questionnaire scores). * Weight change of more than 5 kg in body weight during the last 3 months prior to screening. * Known history of drug or alcohol abuse within 6 months prior to the time of screening. * Patients with hyperthyroidism or uncontrolled hypothyroidism. Note: Patients diagnosed with hypothyroidism need to be on a stable thyroid replacement therapy for at least 6 weeks. * Patients with severe depression according to DSM criteria. * Patients with cognitive impairment (MoCA score \<26). * Severe gastrointestinal disease (e.g. gastroparesis). * Patients previously exposed to a GLP-1 agonist. * Patients with severely impaired renal function (estimated creatinine clearance \<30ml/min). * Patients with a medical history of active liver disease (other than non-alcoholic hepatic steatosis), including chronic active hepatitis B or C (assessed by medical history), primary biliary cirrhosis, or ongoing symptomatic gallbladder disease. * Patients with any clinically significant ECG abnormality. * Laboratory findings at the time of screening: Amylase and/or lipase: \>3 times the upper limit of the normal (ULN) laboratory range ALT or AST: \>3 times ULN Total bilirubin: \>1.5 times ULN (except in case of Gilbert's syndrome) Calcitonin: \>20 pg/mL (5.9 pmol/L) Hemoglobin: \<11 g/dL (male/female) and/or neutrophils \<1,500/mm3 and/or platelets \<100,000/mm3 Triglyceride (TG): \>600 mg/dL (6.78 mmol/L). History of unexplained pancreatitis, chronic pancreatitis or pancreatectomy. * Personal or immediate family history of medullary thyroid cancer or genetic conditions that predispose to medullary thyroid cancer (e.g. multiple endocrine neoplasia syndromes). * Hyperlipidemia. * Females who are pregnant, breast feeding or of child bearing age without effective contraception. * Patients treated per os in the evening by drugs requiring a rapid action (at the discretion of the investigator). * Participants who lack the capacity to give informed consent. * Any medical or psychiatric condition which may compromise participation in the study or the safety, at the discretion of the investigator. * Known abnormality on CT or MRI brain imaging that is considered likely to compromise compliance with any aspect of the trial. * Prior intra-cerebral surgical intervention for PD. * Participant under legal guardianship or incapacitation. * Patients who are participating or have participated in another interventional clinical trial within 30 days prior to baseline. * Previous enrolment in the present trial. * Allergic reaction to the active substance or to any of the excipients of lixisenatide