TY - JOUR T1 - Rare diseases in general practice: recognising the zebras among the horses JF - British Journal of General Practice JO - Br J Gen Pract SP - 550 LP - 551 DO - 10.3399/bjgp16X687625 VL - 66 IS - 652 AU - William RH Evans AU - Imran Rafi Y1 - 2016/11/01 UR - http://bjgp.org/content/66/652/550.abstract N2 - ‘When you hear hoofbeats, don’t expect to see a Zebra.’1The above adage is especially useful in primary care as many of the conditions we see are common. But it is not so useful when we consider our role in both diagnosing and supporting patients with rare diseases. We must be ready to think again and look out for the horse with stripes.A rare disease is defined by an incidence of <5 cases per 10 000 population, however the vast majority of the 7000 rare diseases are far less common.2 Eighty per cent of rare diseases have a genetic basis,3 and genomic research has led to the determination of new diseases at a rate of five each week.4 Despite the vast number of rare diseases, only 100 conditions account for 80% of ‘rare patients’. 2,5 Rare diseases therefore include those that we are familiar with (for example, cystic fibrosis and Guillain-Barré syndrome), and others that may have just a handful of patients worldwide.Most rare diseases are severely disabling, life limiting and affect children, with 30% of patients not reaching their fifth birthday.4 Many patients with rare disease are un/misdiagnosed, particularly those with milder phenotypes presenting at later ages (for example Niemann–Pick disease; Box 1).Box 1. Niemann–Pick disease, type C: a highly variable rare diseaseNiemann–Pick disease, type C (NPC) is a lysosomal storage disorder, historically considered an aggressive neurodegenerative disease of children, with death typically in their teenage years. There is now much wider recognition that the largest subgroup is undiagnosed, with a less aggressive phenotype, presenting later with insidious … ER -