Moreover, extremely rare genetic defects, such as large duplication of the Fibroblast growth factor 9 (FGF9) gene [42], or, on the other hand, Loss-of-Function (LoF) mutations in the female pathway genes i.e., in R-spondin 1 (RSPO1) and Wnt Family Member 4 (WNT4) genes have also been associated with 46,XX SRY– DSD cases [43]. This evidence concerns the gene FGF9 and disorder of sexual differentiation.