transverse process of cervical vertebrae

It is generally assumed that shifts of the boundary of vertebral regions are associated with shifts of Hox expression patterns and, therefore, homeotic transformations of cervical into thoracic vertebrae (C7 transitional vertebra commonly known in humans as cervical ribs) is a common phenotypic abnormality. Homebox ( Hox) genes are involved with this evolutionary mammalian conservation, and have proven to be critical regulators in the establishment of axial skeleton morphology during embryogenesis in all vertebrae classes (Krumlauf, 1994 Wellik, 2007). Due to the relaxation of stabilizing selection through human care, dogs with polydactyly can breed and reproduce despite the strong evolutionary constraint on polydactyly in amniotes (Galis et al. This relaxation of stabilizing selection leading to persistence of features, against which there is normally a strong selection, can also be found in domesticated mammals through artificial selection. 2007 Buchholtz & Stepien, 2009 Varela‐Lasheras et al. Manatees (Trichechus) and sloths (Bradypus and Choloepus) are exceptions to this evolutionary rule (Buchholtz et al. Interestingly, the vertebral count in other regions does vary among mammals, implying there is a selection against variation in the number of cervical vertebrae (Leboucq, 1895 Schulz, 1961). The number of cervical vertebrae in mammals is almost constant at seven, regardless of their neck length (Leboucq, 1895 Schulz, 1961 Starck, 1978 Badlangana et al. Relaxation of the stabilizing selection has likely occurred, and the Pug dog appears to be a good naturally occurring model to further investigate the aetiology of cervical ribs, other congenital vertebral anomalies and numerical alterations.

Higher C7/T1 dorsal spinous processes ratios were associated with the presence of cervical ribs ( P < 0.001), supporting this is a true homeotic transformation. However, Pug dogs with cervical ribs were more likely to have a transitional thoraco‐lumbar vertebra ( P = 0.041) and a pre‐sacral vertebral count of 26 ( P < 0.001). No association was found between the presence of cervical ribs and vertebral body formation defect, bifid spinous process, caudal articular process hypoplasia/aplasia and an abnormal sacrum, which may infer they have a different aetiopathogenesis.

The Pug dog was more affected by cervical ribs than any other breed (46% P < 0.001), and was selected for further analysis. Twenty computed tomography studies from at least two breeds belonging to each of the nine groups recognized by the Federation Cynologique Internationale, including all the brachycephalic ‘screw‐tailed’ breeds that are known to be overrepresented for CVMs, were reviewed. The aim of this study was to describe the prevalence of cervical ribs in a large group of domestic dogs of different breeds, and explore a possible relation with other congenital vertebral malformations ( CVMs) in the breed with the highest prevalence of cervical ribs. By phenotyping we hoped to give clues as to the underlying genetic causes. Mutations in genes upstream of Hox, inbreeding and stressors during organogenesis can also cause cervical ribs. This relatively benign phenotypic change can be associated with fatal traits in humans. Homebox ( Hox) genes are involved in this evolutionary mammalian conservation, and homeotic transformation of cervical into thoracic vertebrae (cervical ribs) is a common phenotypic abnormality when Hox gene expression is altered. The number of cervical vertebrae in mammals is almost constant at seven, regardless of their neck length, implying that there is selection against variation in this number.

Transverse process of cervical vertebrae