However, these two variants lead to different disorders (Table 2) that have different phenotypes and prognoses, which are difficult to distinguish from fetal sonographic indications. FGFR3: c.742C>T is one of the two most common mutations in thanatophoric dysplasia, type I (MIM #187600), while FGFR3: c.1138G>A contributes to more than 90% of the condition in achondroplasia (MIM #100800) patients [23, 24]. This evidence concerns the gene FGFR3 and thanatophoric dysplasia type 1.