The only study that systematically examined structural variation of chromosomes in GTS has karyotyped 68 consecutive patients and has identified one individual with XYY chromosome, and two individuals with normal heterochromatin variations on chromosomes 1 and 9 [66]. Since karyotyping can only detect duplications and deletions larger than 5 megabases, the rate of structural abnormalities could be significantly greater if newer techniques such as chromosomal microarrays (CMA) are utilized. In fact, a recent study of children with Autism Spectrum Disorders has detected abnormal karyotype in 2.2% of patients, and CMA identified deletions or duplications in 18.2% of patients [67]. Although, less than a half of the detected CMA deletions or duplications could be considered as abnormal CNV (variants associated with known genetic disorders), possibly reflecting normal structural variations in the genome [68].
