ABCA4 and Stargardt disease: Certain genetic variants in the ABCA4 gene were identified as responsible for Stargardt disease in 1997 by Allikmets et al.29ABCA4, located on chromosome 1, is a large gene, comprising 50 exons, with an open reading frame of 6819 base pairs and a total genomic length of approximately 140 kilobases.