Orphan diseases list NIH
Rare comes from the Latin rarus (loosely spaced or sparse) and eventually from the putative Indo-European root ERE, denoting separation, as in hermits and eremites and the net-like structures rete, retinaculum, and retina.
Orphan comes from the Greek orphanos (a child deprived of one parent or both, or an adult deprived of a child). Metaphorically it denoted poverty and unspiced food. Its Indo-European root was ORBH (bereft) giving the Latin orbus and the obsolete English words orbation and orbity (orphanhood or childlessness). One bereft of freedom is a slave, forced into hard work, as in the German Arbeit and the Czech robota. Karel Èapek coined the word robot (female robotka) in his play R.U.R. (Rossum's Universal Robots, 1920) to denote an imagined race of mechanical people. And the etymology reflects the link between orphans and the workhouse.
Modern metaphorical meanings of orphan include a discontinued model of a motor vehicle and a line of type beginning a new paragraph at the bottom of a column or page. An orphan virus, such as hepatitis G, is one without a recognised associated disease. Orphan enzymes have catalytic sites that can be occupied by millimolar concentrations of ethanol but have no known physiological roles. Orphan receptors, such as the opioid OP4 receptor identified from gene sequences, have no known endogenous ligands or physiological functions.
Rare diseases—The National Institutes of Health Office of Rare Diseases lists more than 6000, from Aagenaes syndrome to Zuska's disease. The US definition of a rare disease is one that affects less than 200 000 individuals; the corresponding number in Japan is 50 000 and in Australia 2000. These numbers translate to prevalences of 1-8 in 10 000. The European Community definition is less than 5 in 10 000, and the World Health Organization has suggested less than 6.5-10 in 10 000. Below I suggest an alternative.
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