Heterozygous mutations cause LWD and involve about 2.6–12% of cases of ISS.39 LWD is characterized by a variable degree of short stature and milder skeletal dysplasia.70 SHOX is also involved in growth failure documented in individuals with Turner syndrome when the mutation of the X chromosome includes PAR1.71 However, even heterozygous deletions of the downstream and upstream enhancer of SHOX are related to the same phenotype of the SHOX gene defect itself.72 A clinical rule has been developed to identify children with SHOX defects that are suitable for genetic analysis. This evidence concerns the gene SHOX and skeletal dysplasia.