Of 50 patients, 34 had a phenotype compatible with STGD. Of these 34 patients, 27 (79%) had at least 2 pathogenic mutations; 7 of the 34 patients had a single mutation identified, 2 of the 34 had premature termination codons (stop codon and frameshift), and 5 of the 34 had known missense mutations. The identification of a single mutation supports the clinical diagnosis but is not conclusive; however, the carrier rate is estimated to be 1 in 35 to 1 in 50 patients, so we would not expect as many as one-fifth of our patients to be carriers by chance alone. Among the 50 patients, 11 were diagnosed as having STGD by other centers in the past but on current clinical review were reclassified as shown in the Table, reflecting both progression of the disorder and the presence of phenocopies or misdiagnoses. In 5 of the 11 patients, the identification of 2 pathogenic mutations confirmed the historical diagnosis and all had chorioretinal atrophy on current clinical examination, consistent with progression of the disorder.5 One of the 11 patients with chorioretinal atrophy (subject 40) had a single stop codon, again strongly supporting the original clinical diagnosis. Six of the 11 patients did not have pathogenic mutations in ABCA4. Two of the 6 have since been found to have mutations in other genes: CDH3 in subject 416 and CRX in subject 47.7 Subject 49 (with late-onset pattern dystrophy) has a disease-associated allele of unknown mechanism and a missense variant of unknown significance, making the molecular diagnosis in this patient uncertain. In 3 of the 6 patients with a historical diagnosis of STGD and atypical phenotypes (subjects 42, 48, and 50), the molecular diagnosis remains unknown and further investigations are ongoing. Two of 5 patients with bull’s-eye maculopathy had 2 pathogenic mutations, 1 of the 5 had a single known missense mutation, and 2 of the 5 had no mutations, confirming that bull’s-eye maculopathy is genetically heterogeneous. A total of 10 novel mutations were identified (Table).