We present a case study of a 9.5-year-old girl affected by chromosome 12 aberration with the suspicion of juvenile idiopathic arthritis (JIA). All the tests performed at the hospital and the presence of a genetic disorder ledus to search for a diagnosisother than JIA. We initially diagnosed spondyloepiphyseal dysplasia tarda (SEDT), which is related to chromosome 12. Certain signs and symptoms of this disease were presented by our patient at the time of admission. After analysing all the tests and the general conditionof the patient, we were unable to confirm this diagnosis. However, it is possible that the symptoms may occur during subsequentyears and may allow confirmation of SEDT in the future.