This study aims to translate and validate the Gastrointestinal Dysfunction Scale for Parkinson's Disease (GIDS-PD) into Italian to enable the assessment of gastrointestinal symptoms in Italian-speaking patients with Parkinson's disease. The psychometric properties of the translated instrument will be evaluated through a multi-phase process involving translation/back-translation, pre-testing, and large-scale validation across multiple Italian centers

Gastrointestinal dysfunction is a frequent and burdensome non-motor feature of Parkinson's disease, yet validated tools to measure these symptoms are not available for Italian-speaking patients. The study will will undergo three distinct phases, as specified by the MDS guidelines (International Parkinson and Movement Disorder Society, 2023): translation and back-translation (Phase I), pre-test (Phase II), large-scale validation test (Phase III).

• Phase I The translation and back-translation process will be conducted by two independent teams; one team will translate the content from English to Italian, followed by another team independently back-translating it from Italian to English (back-translation).
• Phase II Phase II will involve about 10 PD patients, as heterogeneous as possible, from different Italian regions, and 10 clinicians (PD nurses, neurologists, etc) examiners. The instrument, in this preliminary version, will be presented to a group of about 10 PD patients for the pre-test phase. This phase will be used to establish the basic psychometric properties of the scale and identify items that could potentially be culturally complex.
• Phase III Once the official translation has been approved, the instrument will be administered to a sample of PD patients, native Italian speakers, heterogeneous as far as possible in age and gender.

The final Italian version will be assessed for data quality, acceptability, construct validity, and reliability in a cohort of patients diagnosed with Parkinson's disease across multiple Italian centers.

Inclusion Criteria:

• Age ≥18 years;
• Diagnosis of PD according to the Movement Disorder Society (MDS) diagnostic criteria (Postuma RB et al., 2015);
• Italian-native patients or patients that understand Italian correctly at least;
• Participants mentally and physically able to understand and sign the informed consent form.

Exclusion Criteria:

• Persons in the terminal phase of disease;
• Persons with clinically relevant cognitive impairment;
• Persons diagnosed with Parkinsonism other than PD.

The study population will include patients with PD attending the movement disorders Units of the study centres.