Abstract
Two siblings presented for a second opinion due to progressive reduction in vision. One sibling had been diagnosed incidentally with retinitis pigmentosa and subsequently developed progressive visual dysfunction. This sibling’s exam was notable for best-corrected visual acuity of 20/400 in the right eye and counting fingers the left eye. Dilated fundus exam demonstrated bilateral optic nerve pallor, bone-spicule pigmentations and attenuated retinal arterioles. In contrast, the second sibling presented later in life with progressive visual decline and comparatively less prominent retinal findings. This sibling presented with best-corrected visual acuity of 20/200 in the right eye and counting fingers in left eye. This sibling also demonstrated systemic manifestations including Friedreich’s ataxia without cardiac involvement, thrombocytopenia, pancreatic insufficiency and hypothyroidism. Multimodal retinal imaging including optical coherence tomography and fundus photography with autofluorescence confirmed clear differences in retinal phenotype between the two cases. Further genetic testing identified identical pathogenic MTTP mutation (MTTP c.1783C>T (p.Arg595*)) in both patients. This report demonstrates significant intra-familial phenotypical variability in abetalipoproteinemia-associated retinal degeneration, age of onset and systemic manifestations despite identical MTTP mutation. In addition, this report highlights the importance of differentiating abetalipoproteinemia-associated retinal degeneration from retinitis pigmentosa, given that abetalipoproteinemia is a potentially treatable cause. Both patients were treated with vitamin supplementation and referred for multidisciplinary management.
Presentation Date: 04/23/2026
Issue Date: 04/24/2026
