School of Veterinary Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK.
Department of Veterinary Clinical Science and Services, The Royal Veterinary College, University of London, North Mymms, Hertfordshire, UK.
J Anat. 2018 Aug;233(2):255-265. doi: 10.1111/joa.12822. Epub 2018 May 14.
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. 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. This relatively benign phenotypic change can be associated with fatal traits in humans. Mutations in genes upstream of Hox, inbreeding and stressors during organogenesis can also cause cervical ribs. 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. 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 Pug dog was more affected by cervical ribs than any other breed (46%; P < 0.001), and was selected for further analysis. 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. 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). 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. 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.
哺乳动物的颈椎数量几乎恒定为七个，与颈部长度无关，这表明在这个数量上存在选择压力。同源盒（Hox）基因参与了这种进化上的哺乳动物保守性，当 Hox 基因表达改变时，颈椎向胸椎（颈椎肋骨）的同源性转化是一种常见的表型异常。这种相对良性的表型变化可能与人类的致命特征有关。Hox 基因上游基因的突变、器官发生期间的近亲繁殖和应激源也会导致颈椎肋骨。本研究的目的是描述不同品种的大量家犬中颈椎肋骨的流行率，并探讨与颈椎肋骨发生率最高的品种中其他先天性椎骨畸形（CVM）的可能关系。通过表型分析，我们希望为潜在的遗传原因提供线索。从属于国际犬业联合会认可的九个犬种组中的至少两个犬种的 20 项计算机断层扫描研究被回顾，包括已知 CVM 发生率过高的所有短头颅“螺旋尾”品种。哈巴狗比任何其他品种更容易受到颈椎肋骨的影响（46%；P<0.001），因此被选作进一步分析。没有发现颈椎肋骨的存在与椎体形成缺陷、二分棘突、尾关节突发育不良/缺失和异常骶骨之间存在关联，这可能表明它们具有不同的病因发病机制。然而，患有颈椎肋骨的哈巴狗更有可能有过渡性胸腰椎（P=0.041）和 26 个骶前椎骨计数（P<0.001）。C7/T1 背棘突比例较高与颈椎肋骨的存在相关（P<0.001），这支持这是一种真正的同源性转化。稳定选择的放松可能已经发生，哈巴狗似乎是一个很好的自然发生模型，可以进一步研究颈椎肋骨、其他先天性椎骨异常和数字改变的病因。
