Rare diseases research and practice.

Rare diseases (RDs) affect less than 5 per 10,000 individuals in Europe, while in the USA a rare condition is considered to have a prevalence of fewer than 200,000 affected Americans. RDs stem as one of the most urgent and emerging health problems worldwide, creating a substantial personal, community and financial burden globally. However, available data are only declared on the basis of hearsay evidence, in the absence of strong methodological supports. Creation and implementation of international and national registries could allow the achievement of more reliable data. Disorders of sex development (DSD) are rare and heterogeneous conditions that can be isolated diseases or be part of more complex disorders. Their phenotypic appearance and timing of presentation are quite variable. A wide array of genes has been found to cause DSD, and recent years have witnessed many advances in the diagnosis of patients with DSD with the introduction of chromosomal microarrays and increased availability of gene sequencing. The focus on care and treatment has shifted from early gender assignment and corrective surgery to careful and appropriate diagnosis, proper education of patients and their families, psychological support and individualised treatment driven by a multidisciplinary team. This chapter aims to contribute to the understanding of the fundamental processes of healthcare organisation, research, on-going treatments, prevention and public health policies that regulate and are underlying RDs, including DSD.