TBX1 and autism spectrum disorder 1: However, rare point mutations in the TBX1 gene indicate that TBX1 haploinsufficiency is responsible for most of the physical abnormalities associated with 22q11.2DS, and they have also been associated with attention deficits, mild mental retardation, learning difficulties, developmental delay, Asperger’s syndrome, and depression (2, 3, 4, 5).