Craniosynostosis (CS) is a relatively common birth defect resulting from the 
premature fusion of one or more cranial sutures. Human genetic studies have 
identified several genes in association with CS. One such gene that has been 
implicated in both syndromic (Saethre-Chotzen syndrome) and nonsyndromic forms 
of CS in humans is TWIST1. In this study, a heterozygous Twist1 knock out 
(Twist1(+/-) ) mouse model was used to study the craniofacial shape changes 
associated with the partial loss of function. A geometric morphometric approach 
was used to analyze landmark data derived from microcomputed tomography scans to 
compare craniofacial shape between 17 Twist1(+/-) mice and 26 of their 
Twist1(+/+) (wild type) littermate controls at 15 days of age. The results show 
that despite the purported wide variation in synostotic severity, Twist1(+/-) 
mice have a consistent pattern of craniofacial dysmorphology affecting all major 
regions of the skull. Similar to Saethre-Chotzen, the calvarium is acrocephalic 
and wide with an overall brachycephalic shape. Mutant mice also exhibited a 
shortened cranial base and a wider and shorted face, consistent with coronal CS 
associated phenotypes. The results suggest that these differences are at least 
partially the direct result of the Twist1 haploinsufficiency on the developing 
craniofacial skeleton. This study provides a quantitative phenotype complement 
to the developmental and molecular genetic research previously done on Twist1. 
These results can be used to generate further hypotheses about the effect of 
Twist1 and premature suture fusion on the entire craniofacial skeleton.