IGF1 and atypical Rett syndrome: Examples of the latter include studies examining the effects of insulin-like growth factor – 1 (IGF-1) in individuals with variants in SHANK3 (Phelan-McDermid syndrome) [20] or in MECP2 (Rett Syndrome) [21]; of Rapamycin analogues for NPDs related to TSC1/TSC2 variants (Tuberous Sclerosis Complex) [22] or related to PTEN variants [23]; Arbaclofen in NPDs related to FMR1 variants (Fragile X) [24].