ASD may be part of the clinical presentation of well-characterized genetic syndromes, hereinafter referred to as ASD-related syndromes, such as tuberous sclerosis complex (TSC) [5], fragile X syndrome (FXS) [6], Rett syndrome (RTT) [7,8], Angelman syndrome (AS) [9,10], phosphatase and tensin homolog (PTEN)-related syndromes [11], neurofibromatosis type 1 (NF1) [12], Timothy syndrome [13], 22q13.3 deletion syndrome [14], among others. The gene discussed is PTEN; the disease is atypical Rett syndrome.