Cystinosis is a rare congenital, inherited metabolic disorder that results in the storage of cystine in the cells of many organs of the body. In the infantile nephropathic form of the disease, only the kidney is initially affected by a loss of function, which progresses if untreated and ends in terminal renal failure by early school age. With the prolonged survival of patients due to medication and renal replacement therapy, further loss of function may occur during the course of the disease, especially in the eyes, muscles, endocrine organs and central nervous system. The quality of life of children with cystinosis is an under-researched topic. The results of the studies available so far show that the young patients and their families report a reduced quality of life and sometimes behavioral problems. To date, there are no disease specific patient reported outcome measures (PROMs) to measure the quality of life of patients with cystinosis. The aim of the study is to develop a PROM for this target group in several languages (German, English, Spanish and French) from different countries (Germany, United States, Spain, France). The PROM will focus on quality of life and will be developed for children, adolescents, and young adults including parent-report of parents with children aged 0 to 26 years.