DMD and Intellectual disability: There is now substantial evidence that despite their rarity all patients with mutations involving the Dp71 isoform have severe intellectual disability [27], [32]–[34] and it has been hypothesised that as more distal mutations have the potential to affect the expression of increasing numbers of dystrophin isoforms the severity and frequency of intellectual disability is related to the effect of cumulative loss of functional distal isoforms [33].