Rare Presentation of Attenuated Mucopolysaccharidosis Type IIIA as Isolated Retinitis Pigmentosa

<b>Purpose:</b> To describe a patient presenting in adulthood with isolated retinopathy found to have mucopolysaccharidosis type IIIA. <b>Methods:</b> A single case was evaluated. <b>Results:</b> A 36-year-old man presented with 5 years of worsening peripheral vision and night vision. The initial examination and testing raised concern for rod-cone dystrophy. Genetic testing with an Invitae Inherited Retinal Disorders Panel showed 2 variants of <i>SGSH</i>, which is associated with mucopolysaccharidosis type IIIA. Laboratory testing showed low heparan-N-sulfatase levels and elevated heparan sulfate levels. These results and a thorough review of the literature support a diagnosis of mild attenuated non-neuronopathic mucopolysaccharidosis type IIIA. <b>Conclusions:</b> This case highlights the necessity for collaboration with genetic counselors and the value of a provider's clinical acumen in interpreting genetic testing results. Furthermore, the importance of considering mucopolysaccharidosis type IIIA when adult patients present with new-onset isolated retinitis pigmentosa is emphasized.