Saethre-Chotzen syndrome (acrocephalo-syndactyly type III, ACS III) is an autosomal dominant craniosynostosis with brachydactyly, soft tissue syndactyly and facial dysmorphism including ptosis, facial asymmetry and prominent ear crura. ACS III has been mapped to chromosome 7p21-22. Of interest, TWIST, the human counterpart of the murine Twist gene, has been localized on chromosome 7p21 as well. The Twist gene product is a transcription factor containing a basic helix-loop-helix (b-HLH) domain, required in head mesenchyme for cranial neural tube morphogenesis in mice. The co-localisation of ACS III and TWIST prompted us to screen ACS III patients for TWIST gene mutations especially as mice heterozygous for Twist null mutations displayed skull defects and duplication of hind leg digits. Here, we report 21-bp insertions and nonsense mutations of the TWIST gene (S127X, E130X) in seven ACS III probands and describe impairment of head mesenchyme induction by TWIST as a novel pathophysiological mechanism in human craniosynostoses.

Although it is currently thought that surgery is indicated mainly for cosmetic reasons in isolated craniosynostoses, the functional aspects of the treatment must not be underestimated. Prospective studies on intracranial pressure and mental evolution of these children have shown that there were functional consequences in a significant proportion of cases even of single suture fusion. The frequency of increased intracranial hypertension and the risk of mental impairment depend on the age of the child and the type of craniosynostosis. In nonsyndromic cases, the higher risks are observed in multisutural craniosynostoses (brachycephaly, oxycephaly). In syndromic cases, the risk of intracranial hypertension is higher in Crouzon syndrome, and Apert syndrome carries the higher risk of mental retardation. The study of a personal series of 2,137 craniosynostoses shows that the functional and the cosmetic results are better after early surgery, and that the operative risks are not higher in infants than in older children.

From a series of 1265 individuals with different craniosynostoses hospitalized between 1976 and 1993, 260 probands with nonsyndromic unilateral (181) or bilateral (79) coronal synostosis were analysed. The prevalence of craniosynostoses was estimated as 1 in 2100 children. In the group of coronal synostosis, family history was obtained on 192 probands in 180 pedigrees. The male:female ratio was 1:2. The average paternal age was 32.7 +/- 6.4 years, which is significantly higher than normal. In 26 of the 180 pedigrees, a high degree of familial aggregation was observed, giving a 14.4% figure of familial cases. The bicoronal synostoses were significantly more often familial than the unicoronal synostoses. Segregation analysis of these families leads to the conclusion that coronal synostosis is transmitted as a dominant disorder with 0.60 penetrance and 61% of sporadic cases.