A nonconsanguineous Turkish family (family A) with three siblings affected by COD and CRD and an isolated Dutch individual (family B) with ACHM that evolved into a progressive retinal dystrophy were included in this study (Figure 1A). These families belong to a large cohort of individuals affected by ACHM (n = 21), COD (n = 110), or CRD (n = 112). Most of the probands are the only affected persons in their family, and they were ascertained in various ophthalmic centers in the Netherlands, Belgium, the United Kingdom, and Canada. The individuals diagnosed with ACHM had a history of congenital pendular nystagmus, reduced visual acuity, photophobia, and poor or absent color vision in early infancy and had absent cone function (but normal rod responses) on ERG. Individuals in our cohort were classified as having COD when they presented with a childhood or early-adult-onset progressive deterioration of visual acuity and color vision, reduced cone responses on ERG, and normal rod responses for ≥5 years.6 Inclusion criteria for CRD were progressive loss of central vision, color-vision disturbances, and a reduction of both cone (equally or more severely reduced) and rod responses on ERG.6