Screw tail

Malformations and fusion of the vertebrae, which result in a kinked tail and shortening of the tail by approximately 8 to 15 vertebrae, is called a screw tail. In some breeds, such as the English Bulldog, French Bulldog and Boston Terrier, the screw tail is a characteristic feature, but in other breeds it is undesirable as it may be associated with other health problems, including brachycephalic airway obstruction syndrome, malformation of the thoracic vertebrae and congenital heart disease. Screw tail has so far been reported in English Bulldog, American Bulldog, French Bulldog, American Pit Bull Terrier, American Staffordshire Terrier, Staffordshire Bull Terrier, Boston Terrier, Bordeaux Great Dane and Shih Tzu. Although the Pug breed also has a screw tail, it is not a screw tail as the tail is normal length and free of vertebral malformations.

The screw tail is caused by deletion c.2044delC in the WNT pathway gene Dishevelled 2 (DVL2), which leads to a shift in the reading frame, premature inclusion of the stop codon and the formation of a truncated non-functional DVL2 protein that plays a role in Wnt signalling.

Screw tail is a recessively inherited disease. The disease develops in dogs which inherit the mutated gene from each parent.  These dogs are designated as P/P (positive/positive). The carriers of the mutated gene are designated as N/P (negative/positive). The carriers inherited the mutated gene from one parent only and are without clinical signs. However, they pass the disease on to their offspring.  When mating two heterozygotes (N/P), there will be theoretically 25% of the offspring healthy, 50% of the offspring will be carriers and 25% of the offspring will inherit the mutated gene from both parents and will be affected by Screw tail.  Mating one healthy dog (N/N) with a carrier of this mutation (N/P) will theoretically produce 50% carriers and 50% healthy offspring.  If a carrier (N/P) is mated with an affected dog (P/P), there will be theoretically 50% affected dogs and 50% carriers.

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Reference:

Mansour, T.A., Lucot, K., Konopelski, S.E., Dickinson, P.J., Sturges, B.K., Vernau, K.L., Choi, S., Stern, J.A., Thomasy, S.M., Döring, S., Verstraete, F.J.M., Johnson, E.G., York, D., Rebhun, R.B., Ho, H.H., Brown, C.T., Bannasch, D.L.: Whole genome variant association across 100 dogs identifies a frame shift mutation in DISHEVELLED 2 which contributes to Robinow-like syndrome in Bulldogs and related screw tail dog breeds. PLoS Genet 14:e1007850, 2018. Pubmed reference: 30521570.