STX1A and Visual impairment: The human STX1A gene is situated on chromosome 7q11.2, and the deletion of a 1 centimorgan region on this chromosome, encompassing the STX1A gene, is associated with Williams syndrome (Nakayama et al., 1997, 1998; Botta et al., 1999), characterized by cognitive phenotypes, cardiovascular anomalies, and visual impairment (Bellugi et al., 1999; Botta et al., 1999; Castelo-Branco et al., 2007).