Axial Skeleton Segmentation Serial Homology Module

A conserved developmental-patterning module, the axial counterpart of the limb/digit and pharyngeal-arch serial-homology modules. The vertebrae and ribs are serially repeated (metameric) elements derived from somites, which bud off the presomitic mesoderm one pair at a time under the control of the segmentation clock — an oscillator built from coupled Notch, Wnt, and FGF signaling — interacting with a posterior-to-anterior FGF/Wnt determination wavefront. Because the same periodic mechanism builds every segment, a single lesion in the clock or its Notch components (DLL3, MESP2, LFNG, HES7, TBX6) perturbs many segments at once and produces a coordinated multi-segment malformation bundle — multiple hemivertebrae, fused/block vertebrae, and rib fusions or malalignment across the axial skeleton — rather than an isolated single-segment defect. The spondylocostal/spondylothoracic dysostoses and related congenital vertebral malsegmentation disorders differ in the specific Notch-pathway gene but converge on this clock-to-malsegmentation chain. Conforming disorder entries declare conformance via conforms_to, substituting the disorder-specific segmentation-clock gene while preserving the perturbed-segmentation-to-serially-homologous-malsegmentation chain.