For example, Albert et al., differentiated fibroblasts that were taken from patients with Stargardt Disease into photoreceptor precursor cells (PPCs) to investigate two deep intronic variants (ABCA4 c.4539+2001G>A and c.4539+2028C>T) which cause a 345 nucleotide pseudoexon insertion resulting in a frameshift (p.Arg1514Leufs*36) [48]. Here, ABCA4 is linked to Stargardt disease.