FGFR1 and Hartsfield-Bixler-Demyer syndrome: Interestingly, FGFR1 loss-of-function mutations have been shown to give rise not only to KS but also to several other human genetic conditions, such as isolated HH or Hartsfield syndrome, a disorder characterized by the co-occurrence of holoprosencephaly and ectrodactyly, in association with developmental delay/intellectual disability, agenesis of corpus callosum, genital anomalies, and variable skeletal malformations (Simonis et al. 2013).