A Rare Case of Hunter Syndrome (Mucopolysaccharidosis II) With Bilateral Maculopathy Associated With Rod-Cone Dystrophy

Hunter syndrome is an X-linked recessive lysosomal storage disorder that is caused by a mutation in the iduronate sulfatase gene. Both anterior and posterior segment abnormalities are found as a result of the accumulation of glycosaminoglycans in ocular tissues. Retinal dystrophy, particularly rod-cone dystrophy, has a major effect on visual acuity, leading to significant visual impairment as the condition worsens. We report a case of a 53-year-old male patient of Asian descent previously diagnosed with Hunter syndrome, who presented with progressive difficulty in visual tracking and colour recognition. Fundus examination revealed bull's eye maculopathy in both eyes. Optical coherence tomography revealed severe attenuation of the outer retinal layers at the macula. Electrophysiological tests showed reduced photopic and scotopic responses, with P50 responses severely attenuated, and visual field testing showed a central scotoma in both eyes. Patients with Hunter syndrome can present with retinitis pigmentosa or rod-cone dystrophy. Accumulation of glycosaminoglycans in the retinal pigment epithelium results in photoreceptor loss, affecting both rods and cones. Maculopathy associated with rod-cone dystrophy may be associated with this condition.