GTF2I and Cognitive impairment: Initially, the examination of visuospatial performance by HR and JB seems indicative of the additive effect of deleting each of the GTF2I family genes on the severity of cognitive impairment, and is in line with other findings in individuals with extended deletions (approximately 1.8 Mb) that encompass GTF2IRD2, who present with significantly greater neurological impairments than individuals with shorter deletions typical of WS [59].