The TWIST gene maps to 7p21 and mutations in the gene have been reported in the 
Saethre-Chotzen form of craniosynostosis. The position of the Saethre-Chotzen 
gene has previously been refined by FISH analysis of four patients carrying 
balanced translocations involving 7p21 which suggested that it was located 
between D7S488 and D7S503. We report here that the breakpoints in four 
translocation patients do not interrupt the coding sequence of the TWIST gene 
and thus most likely act through a positional effect. Twelve Saethre-Chotzen 
cases were found to have TWIST mutations. Four of these families had been used 
as part of the linkage study of the Saethre-Chotzen locus. The mutations 
detected included missense and nonsense mutations and three cases of a 21 bp 
duplication. Although phenotypically diagnosed as having Saethre-Chotzen 
syndrome, three families were found to have a pro250arg mutation of FGFR3.