Mucopolysaccharidosis type I with retinal degeneration and absence of corneal involvement in the eighth decade of life

INTRODUCTION: Mucopolysaccharidosis type I (MPS I) is an autosomal recessive lysosomal storage disorder caused by mutations in IDUA, resulting in ⍺-L-iduronidase loss of function and glycosaminoglycan accumulation. Corneal clouding is the most consistent ocular manifestation and often prompts diagnostic evaluation. Retinal degeneration associated with MPS I has also been reported. The extent to which corneal clouding may be absent in MPS I, particularly in late adulthood, remains incompletely characterized. METHODS: Case report. RESULTS: We report a 71-year-old woman referred for longstanding pigmentary retinopathy with a history of early-onset aortic stenosis. Ophthalmologic examination demonstrated clear corneas bilaterally without evidence of corneal clouding. Multimodal retinal imaging revealed widespread pigmentary changes and retinal thinning, and full-field electroretinography showed markedly reduced rod responses, electronegative mixed responses, reduced cone and flicker responses, and reduced cone bipolar ON/OFF responses. Whole exome sequencing identified compound heterozygous IDUA variants c.1205G>A (p.W402*) and c.536C>T (p.T179M), supporting a diagnosis of MPS I. DISCUSSION: This case illustrates an unusually attenuated MPS I presentation characterized by very late diagnosis, absence of corneal clouding, and retina-predominant ocular involvement. These findings expand the recognized phenotypic spectrum of MPS I and highlight the importance of considering lysosomal storage disorders in patients with syndromic or atypical retinal degeneration, even in older adults.