Editor—Retinopathy of prematurity (ROP) is the commonest cause of potentially preventable blindness in infants.1 2 In developed countries this may reflect the increasing survival of ever more premature babies.3 In emerging countries this may reflect the recent provision of neonatal care.4 5 There is, however, evidence that a genetic component may be involved in the development of severe ROP. For example, the incidence of severe ROP is higher in white infants than in Afro-Caribbean infants in both the United Kingdom6 and the United States.7 There is also great variation in the incidence of severe ROP in different developed countries. In Israel, the incidence of threshold ROP (stage 3 plus or worse) in infants weighing >1000 g is 26%, but none progressed to severe visual loss.8 A similar study in Denmark, however, reported that of 170 infants weighing <1500 g, threshold ROP developed in 26.5% and that 40% of these infants went on to stage 5 ROP despite intervention.9

Norrie disease is an X linked recessive disorder, which is characterised by bilateral retinal dysplasia with retinal detachment, resulting in congenital blindness.10 In addition, approximately one third of patients develop sensorineural hearing loss and a variable spectrum of mental retardation.11 The causative gene for Norrie disease is the NDPgene.12 13 Recently, in a cohort of American patients, mutations in exon 3 of the Norrie's disease protein gene (NDP) have been associated with advanced ROP.14 We undertook a study to determine whetherNDP mutation may be a factor influencing disease severity in a cohort of patients undergoing investigation in the UK. Such an association would contribute to developing a better understanding of ROP pathophysiology and would provide paediatric ophthalmologists with an adjunctive diagnostic test for predicting likely progression of …