Rare diseases represent a major public health challenge due to their number, presently estimated to be between 6000 and 8000, their severity and the absence of any preventive treatment. The enactment of two National Plans for Rare Diseases by the establishment of Referral Centers and Diagnosis and Treatment Centers has brought about a recognition of the specificity of these disorders, the creation of a epidemiological database, a framework for rapid diagnosis protocols at the first symptoms, greater access to specialized care to accompany the afflicted and their families during their frequently difficult medico-social journey, training of skilled health professionals in the field of these rare diseases, promotion of basic and clinical research and finally the development of European partnerships in both research and therapeutic planning.

The dental surgeon can feel inadequate when confronted with a rare disease: (a) difficult diagnosis, (b) therapeutic complexity, (c) and questioning by the parents, are three major obstacles that we have to overcome in order to carry out our therapy. Even if the field of genetics has made major advances during the last few years, it is clinical knowledge, above all, that leads us to a diagnosis. Certain syndromes present with very subtle signs which alone can appear trivial but which, taken together, defines a pathological entity. To know or to discover these signs and to recognize them is therefore the first challenge.

Orthognathic surgery, is often required for patients with rare diseases in order to normalize occlusion that is generally severely affected. There is no one specific surgical approach because anomalies encountered in this population often require various complex technical procedures. Unlike common dental malocclusions, agenesis, skelettal dystrophies and functional problems are gathered. Orthodontic preparation, before surgery, is made difficult, resulting in a challenging treatment process. In certain cases, the stability of the result can be uncertain due to major dysfunctions. However, given the functional as well as morphological improvement that these procedures bring about, they should be planned if the dysmorphia is significant.

Hypohidrotic ectodermal dysplasias (HED) are a heterogeneous and complex group of syndromes characterized by a dental craniofacial phenotype associated with severe oligodontia, maxillary hypoplasia with broad face and most notably facial concavity. Cephalometric analyses show insufficient maxillary sagittal growth, a protruded mandible, reduced facial and ramus heights, as well as basicranial changes. Early diagnosis and care from a multidisciplinary team are essential. In the primary dentition, initial prosthetic treatment is recommended and may possibly be combined with interceptive orthodontic treatment. In the mixed dentition, treatment of a transverse maxillary deficiency consists in installing a removable expander or a quadhelix in the case of moderate phenotypes where there is adequate anchorage support. To achieve mandibular anterior repositioning of the maxilla the patient must wear a facial mask. In the permanent dentition, the important steps are correlated with the pre-implant and pre-prosthetic orthodontic adjustments, as well as the presurgical orthodontic preparation that precedes subsequent single or double jaw orthognathic surgery. Temporary skeletal anchorage with mini-screws or plates can be used in cases of insufficient anchorage.

The development of predictive medicine for dentistry is very promising but there are potential abuses as well. Given that genetic testing is at the forefront of predictive medicine, legislation has been established governing activity related to genetics that is both open to the advances that genetic testing can provide and, at the same time, respectful of the fundamental rights of patients and in particular of the rights of minors.