Mutated MESP2 causes spondylocostal dysostosis in humans

Spondylocostal dysostosis (SCD) is a term given to a heterogeneous group of disorders characterized by abnormal vertebral segmentation (AVS). We have previously identified mutations in the Delta-like 3 (DLL3) gene as a major cause of autosomal recessive spondylocostal dysostosis. DLL3 encodes a ligand for the Notch receptor and, when mutated, defective somitogenesis occurs resulting in a consistent and distinctive pattern of AVS affecting the entire spine. From our study cohort of cases of AVS, we have identified individuals and families with abnormal segmentation of the entire spine but no mutations in DLL3, and, in some of these, linkage to the DLL3 locus at 19q13.1 has been excluded. Within this group, the radiological phenotype differs mildly from that of DLL3 mutation–positive SCD and is variable, suggesting further heterogeneity. Using a genomewide scanning strategy in one consanguineous family with two affected children, we demonstrated linkage to 15q21.3-15q26.1 and furthermore identified a 4-bp duplication mutation in the human MESP2 gene that codes for a basic helix-loop-helix transcription factor. No MESP2 mutations were found in a further 7 patients with related radiological phenotypes in whom abnormal segmentation affected all vertebrae, nor in a further 12 patients with diverse phenotypes.