Amino acid sequence. Amino acid sequence alignment of mammalian sequences encoding ABCA1, ABCA2, ABCA3, ABCA4, ABCA7 and C elegans ced7, spanning the region mutated in the SS patient. The mutated residue (ABCA1 R1925Q) is indicated by a rectangle. The Walker A motif of the ATP-binding domain is marked. The asterisk depicts a 2-amino acid deletion found in a patient with HDL deficiency.