Rare diseases by definition are conditions that affect small numbers of people. The prevalence threshold that designates a disease as rare varies in different countries. Generally, diseases with prevalence fewer than 5 in 10,000 people are considered rare. 1 Many rare diseases affect far fewer people worldwide, with some having a single identified case and others with cases numbering from tens to low hundreds of people. 2 However, collectively, they are common. There are 6,000–8,000 rare diseases, with 250–280 new diseases described annually, affecting an estimated 6–8% of the human population. 3–6 The rarity of these diseases individually creates significant challenges for affected patients, their families, and for clinicians attempting to achieve a confirmed diagnosis and implement best care. 7, 8 Obtaining a correct diagnosis is frequently a difficult and lengthy process, as physicians and caregivers often lack appropriate expertise in a disease that they rarely encounter. 4 Effective therapeutics are lacking for the large majority of these diseases, and when they exist, they are often very expensive because of scientific and manufacturing challenges, and small potential markets for such products; this creates barriers to access that are frequently difficult to resolve. 3 Rare diseases are chronic and often severely disabling, thus treating these patients places a substantial burden on healthcare budgets. For example, one recent study from Western Australia concluded that in 2010 the state population affected by a limited cohort of only 467 rare diseases represented 2% of the population but 10.5% of in-patient hospital costs. 9 Therefore, improved diagnostics and targeted therapeutics that keep these patients healthier and reduce their time in medical facilities would be highly beneficial. Many rare diseases resemble common ones and involve the same genetic pathways, but are generally more aggressive or severe in their presentation. Improved understanding of these diseases may therefore be relevant to improving or developing diagnostics and therapeutics for their more common counterparts.