This is true for Stargardt disease (STGD1) (MIM 248200), which is caused by pathogenic variants in the gene encoding the adenosine triphosphate (ATP) binding cassette type A4 (ABCA4) (MIM 601691)10 as biallelic variants can be found in the majority of the cases11 and in a smaller proportion of other IRD subtypes.12–14 In ~30% of STGD1 cases, however, the expected second ABCA4 variant was lacking. The gene discussed is ABCA4; the disease is severe early-childhood-onset retinal dystrophy.