Orthodontic treatment of a nine-year-old patient with hypophosphatemic rickets diagnosed since the age of two: A case report Miltiadis A. Makrygiannakis 1 , Mahmoud Dastoori 2 , Athanasios E. Athanasiou 3,4 1. Department of Orthodontics, School of Dentistry, National and Kapodistrian University of Athens, Athens, Greece 2. Dubai London Clinic, Dubai, United Arab Emirates 3. Department of Dentistry, European University Cyprus, Nicosia, Cypruss, Nicosia, Cyprus 4. Hamdan Bin Mohammed College of Dental Medicine, Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, United Arab Emirates Correspondence: Miltiadis A. Makrygiannakis, Department of Orthodontics, School of Dentistry, National and Kapodistrian University of Athens, Athens, Greece. makrygiannakis.orthodontics@gmail.com Keywords Rare diseases X-linked hypophosphatemia XLH Orthodontics Summary Hypophosphatemic rickets (HR) is a genetic disorder with various types of inheritance. It results mainly from defects in factors that control mineral ion homeostasis such as 1,25(OH) 2 D (Calcitriol) and FGF23 (Fibroblast Growth Factor 23). The existing bibliography regarding orthodontic treat- ment in patients with hypophosphatemic rickets is extremely limited. The aim of this case report is to describe the orthodontic treatment of a 9-year old Caucasian female patient suffering from HR. The patient presented a healthy late mixed dentition and periodontium. She suffered from a mild Class III maxillary skeletal pattern. There was a bilateral posterior crossbite, short lingual frenulum, a right maxillary mesioposition with a Class II subdivision on this side and a moderate space deficiency in the dental arches. The disorder was controlled by medication. In specific, patient was taking 1.5 mL of phosphate four times per day, 0.3 mL of calcitriol twice per day and 50,000 IU of Vitamin D3 on a weekly basis. Given the Class III skeletal pattern, the medical condition and the absence of relevant bibliography, it was decided to perform maxillary expansion, facemask traction and orthodontic treatment with fixed appliances. By the end of treatment, Class I canine and molar relationships were achieved, overjet and overbite were corrected and space deficiency was addressed in both arches. PAR index was 27 at the beginning of treatment and became 2 by the end of treatment (92.5% correction). The aesthetic component of IOTN was 4 and changed to 1, while the dental component used to be 5i and became 2g. With regards to retention, upper and lower fixed retainers from canine to canine and upper and lower vacuum formed appliances were used. In conclusion, a patient with controlled HR was orthodontically treated in a successful way. Orthodontic therapy was performed in a minimally invasive manner. Thus, HR does not constitute a contraindication for orthodontic treatment, when the disorder is kept under control. Available online: 5 August 2020 tome 18 > n83 > September 2020 https://doi.org/10.1016/j.ortho.2020.06.003 © 2020 CEO. Published by Elsevier Masson SAS. All rights reserved. 648 Case Report International Orthodontics 2020; 18: 648–656 Websites: www.em-consulte.com www.sciencedirect.com