Wild-type SMARCAL1. SMARCAL1, which is 954 amino acids in length, has several critical domains, including an N-terminal DNA binding domain (RPA) comprised of the first 34 amino acids of the protein; two HARP domains, each 55 amino acids in length and connected by a 40 amino acid linker, that are critical for annealing helicase activity; and an ATPase enzymatic domain, separated from the second HARP domain by 47 amino acids and divided into two regions by a 115 amino acid chain, necessary for ATP hydrolysis. Our patient’s S859P missense mutation is predicted to lie just within the C terminal boundary of the ATPase domain (*).