Mae'r dull confensiynol o werthuso meddyginiaethau wedi bod yn heriol o ran clefydau prin lle mae niferoedd y cleifion yn isel iawn.  Cyfeirir at y meddyginiaethau hyn fel arfer fel meddyginiaethau amddifad a thra amddifad.  Er bod rhaglen technolegau arbenigol iawn NICE yn anelu at ymdrin â rhai meddyginiaethau tra amddifad - a'r bwriad yw mabwysiadu'r cyngor hwn lle y bo'n briodol - mae bwlch yn parhau wrth ddatblygu'r sylfaen dystiolaeth ar gyfer meddyginiaethau amddifad a thra amddifad.  Dyma pam y comisiynwyd adolygiad o'r broses werthuso ar gyfer y triniaethau penodol hyn.  Ymgynghorwyd ynghylch yr adroddiad a gofynnwyd i Gadeirydd AWMSG wneud y gwaith sydd ei angen i ddatblygu a gweithredu ymagwedd system gyfan at adnabod, gwerthuso a monitro'r grŵp hwn o feddyginiaethau; gyda'r nod o sicrhau bod cleifion gyda chlefydau prin yn cael mynediad teg a chyfartal at driniaethau priodol sy'n seiliedig ar dystiolaeth.
The conventional approach to appraising medicines has proved challenging in respect of rare diseases where patient numbers are very low. These medicines are normally referred to as orphan and ultra-orphan medicines. While the NICE highly specialised technologies programme aims to cover some ultra orphan-medicines - and the intention is to adopt this advice where appropriate - there remains a gap in developing the evidence base for orphan and ultra-orphan medicines. This is why a review of the appraisal process for these particular treatments has been commissioned. The report has been consulted on and the chair of AWMSG has been asked to undertake the work required to develop and implement a whole-system approach to the identification, appraisal and monitoring of this group of medicines; the aim being to ensure that patients with rare diseases have fair and equitable access to appropriate, evidence-based treatments