Unusual presentation of cone dysfunction consequent upon a homozygous FAM161A variant

To describe the features of cone dysfunction in a patient who harbors a homozygous frameshifting variant in FAM161A.

A 20-year-old male presented with subnormal vision, photophobia, nystagmus, and loss of color vision. Fundus imaging showed bilateral subtle macular pigmentary mottling and mild retinal vascular attenuation. Macular optical coherence tomography showed bilaterally hyporeflective ellipsoid zone layers. Electroretinography revealed isolated cone dysfunction with preservation of scotopic responses, with no deterioration over 3 years of follow-up. Whole-exome sequencing revealed a homozygous 1-bp insertion: c.496dupT p.(Ser166Phefs *10) in exon 3 of FAM161A.

FAM161A retinopathy could present initially as cone dysfunction in patients whose fundi appear to be relatively normal, and it may be considered in the differential diagnosis of cone dysfunction syndrome.