IMPG1 and Nystagmus: This study investigates the phenotypic impact of dual-gene variants, including biallelic ABCA4 variants and additional retinal gene variants in CACNA1F, IMPG1, HK1 and MYO7A. In MST465-II:1, the ABCA4-CACNA1F constellation led to progressive macular atrophy and night blindness, with nystagmus linked to CACNA1F. In MST448-II:1, ABCA4 variants primarily contributed to a macular dystrophy, while the IMPG1 variant had no obvious impact, suggesting it may be a benign polymorphism.