1Department of Anthropology, California State University East Bay, 2Institute for Dental History and Craniofacial Study, A. A. Dugoni School of Dentistry, University of the Pacific, 3Department of Biomedical Sciences, A. A. Dugoni School of Dentistry, University of the Pacific, 4Department of Anthropology, University of California, San Diego, 5Department of Anthropology, University of California, Berkeley
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Osteochondrodystropies are a class of skeletal deformities resulting from specific genetic mutations. Abnormal COMP and FGFR3 gene expression impacts cartilage ontogeny, resulting in multiple epiphyseal dysplasia/pseudoachondroplasia and achondroplasia (respectively). Impacts of FGFR3 mutations on cranial cartilages are known, whereas there is little understanding of abnormal COMP expression in cranial development. We investigate the impact of a COMP mutation on skull development and compare it to FGFR3 changes.
Archaeologically derived individuals expressing COMP and FGFR3 characteristics (n=3) were examined. Our normal sample comprises both sexes and representatives of similar populations (n=45). We made a series of metric measurements for skull comparisons. We also evaluated the skulls against condition-specific nonmetric features compiled from the literature.
COMP individual have an enlarged cranial circumference but normal cranial length/breadth. They also have a slightly enlarged frontal breadth, possibly related to the enlarged circumference. FGFR3 expression in the cranium shows a different pattern, with increases in the cranial breadth/length but not in the circumference. FGFR3 and COMP mutations are also expressed differentially in the cranial base.
Mutations in COMP have been considered to have no or only minor impacts on skull development. Here we document cranial modifications of the nasal capsule-parachortal plate that we believe are related to mutation of the COMP gene. In later development, these basicranial changes result in a modified cranial shape that is similar to, but different from, that occurring in FGFR3 mutations. We suggest that COMP gene expression in late fetal stages may result in this unique suite of cranial modifications.