Table 4. A summary of UODs definitions is provided based on the country.

Country, frequency		(UOD) definition	Date
UK	NICE	Drugs with indications for conditions with a prevalence of less than 1 per 50 000 persons
Scotland	The Scottish government	New definition of ultraorphan medicines that can treat very rare conditions affecting fewer than 1 in 50 000 people—approximately 100 people or fewer in Scotland
England		HST for ultra-orphan indications Euro113,900–3 41 700/QALY in England
	WHO	WHO recommends a WTP of <3 times GDP per capita/QALY
Scotland		New definition for ultra-orphan drugs: medicines that are used to treat a condition with a prevalence of 1 in 50 000 or less or around 100 people in Scotland, which will mostly be used to facilitate early access programs and reimbursement processes	Effective from October 2018

GDPgross deomestic productHSTHighly Specialised TechnologiesNICENational Institute for Health and Care ExcellenceQALYquality-adjusted life yearUODultraorphan drugWTPwillingness to pay