Introduction: Chondrodysplasias are a heterogeneous group of genetic pathologies, characterized by changes in cartilage, which translate into abnormal skeletal development. Inside this group are the metaphyseal chondrodysplasias (MCDs), whose skeletal disorders mainly disturb the growth of long bones. Both the classification and diagnosis of these pathologies are based on clinical, radiological, and genetic aspects. In the MCDs, there is a group called type II collagenopathies, resulting from mutations in the gene that encodes the alpha-1 chain of type II collagen, the COL2A1 gene, culminating in an essential deficit for the endochondral ossification process. Therefore, these individuals suffer from disturbances in the epiphyseal plates, in the nucleus pulposus, and in the vitreous humor. Spondyloepimetaphyseal Dysplasia Strudwick type (SEMD) is a rare autosomal dominant entity. Clinically characterized by disproportionate short stature, pectus carinatum, scoliosis, lordosis, myopia, retinal detachment, equinovarus, genu valgum, coxa vara, hip arthritis, and even cleft palate, although there are cases described with normal craniofacial appearance. Radiographically, alterations such as metaphyseal dappling, atlantoaxial instability, hypoplasia of the odontoid process, platyspondyly and epiphyseal defects in the femur and tibia, among others, are detectable. Studies of MCDs at the orthodontic level are scarce and directed to specific subtypes, due to their low prevalence, and cases of orthodontic treatment (OT) in individuals with SEMD are absent in the literature.  
Objective: This clinical case aims to demonstrate the importance of orthodontic diagnosis and correct planning of treatment timings in rare cases of craniofacial deformity. Case Report: A 14-year-old male patient with a history of SEMD and sleep apnea was referred for orthodontic treatment. Physical examination showed characteristic disproportionate short stature with genu valgum, coxa vara, pectus carinatum, and a face with mid-third hypoplasia, retrognathia, depression of the nasal bridge, and dental crowding. The main orthodontic problems observed were SEMD, skeletal and hyperdivergent class II, apical and buccal position of teeth 1.3 and 2.3, lack of maxillary and mandibular space, increased overjet and overbite, accentuated mandibular curve of Spee and deep bite. OT was planned with fixed multibracket appliances, transpalatal bar and extraction of the first premolars in the upper jaw. In the mandible, in addition to the multibrackets fixed appliance, stripping was performed.
Results: In the short term, correction of crowding, overjet, overbite and smile line was achieved, and canine class I, molar class II and canine guides were obtained. In the medium and long term, it was possible to prevent temporomandibular joint pathology, improve the occlusal relationship, chewing and the patient's facial aesthetics.
Conclusion: It is important that dentists, orthodontists and maxillofacial surgeons are conscious of this type of pathology in order to adapt OT to the severity of craniofacial anomalies, functional pathologies, and existing aesthetic alterations. In this way, it is possible to provide functional occlusion, improved facial appearance and quality of life in patients with MCD.