Non syndromic cleft lip and palate (CLP) is the most frequent human malformation. CLP is of complex inheritance and at least twenty contributing chromosomal regions have been identified by linkage studies. On the other hand, mutations in several genes such as TWIST and FGFR2 result in syndromic cranio-facial abnormalities of highly variable range. It is our hypothesis that some mutations at TWIST might contribute to CLP in absence of other dysmorphic features. Thus, DNA biopsies of patients with non syndromic CLP are collected and prepared to search for allelic variations or mutations at TWIST. This study should contribute to improve the classification of facial malformations relative to gene, to help to a better understanding of the inheritance pattern of this pathology, to help to genetic counselling for some cases aiming at the prevention of genetic disease. This project is based on a close cooperation between the Orthodontic Department, the Paediatric Surgery Department and the Center for Clinical Investigation (University Hospital in Strasbourg), in a joint project with an academic research laboratory, expert in molecular biology and genetics.