Screwtail, Curly Tail (DVL2-related)

Gene: DVL2

Transmission: Autosomal recessive

For an autosomal recessive genetic disease an animal must have two copies of the mutation in question to be at risk of developing the disease.  Both parents of an affected animal must be carriers of at least one copy of the mutation.  Animals that have only one copy of the mutation are not at risk of developing the disease but are carrier animals that can pass the mutation on to future generations.

Mutation: Deletion, DVL2 gene: c.2051 del.C, p.(Pro684Leu frameshift STOP 26), exon15, Chr.5.

Medical system: Skeletal

Breeds: English Bulldog, French Bulldog, Boston Terrier, Americal Pit Bull Terrier, Staffordshire Bull Terrier, Shih Tzu, Cane Corso

Age of onset of symptoms: From birth (congenital)

The curly tail (screwtail) phenotype of shortened, kinked tail is a breed standard for several dog breeds, mention the related Bulldog (English Bulldog), French Bulldog and Boston Terrier breeds.  The curly tail phenotype is caused by caudal vertebral anomalies including the malformation, fusion or absence of vertebrae.  In addition, thoracic vertebral anomalies can be present, including wedge shaped (hemi-vertebrae) resulting in scoliosis. The screwtail phenotype is associated with health problems including skin fold infections, possible neurological problems including incontinence, and an increased susceptibility of intervertebral disc disease.  Although the curly tail phenotype in these breeds is also associated with the brachiocephalic (short nose) phenotype, not all brachiocephalic dog breeds are curly tail breeds.

Genomic studies were undertaken in screwtail breeds to determine the molecular cause of this phenotype, and a mutation in the DVL2 gene was identified.  The DVL2 gene codes for a protein involved in cell-cell communication pathways that are important during embryonic development.  Bulldogs and French Bulldogs were found to be fully fixed for the mutation, while Boston Terriers were found to have a high frequency of double mutants (M/M = 94%).  In these breeds, the mutation was fully penetrant for the caudal screwtail phenotype, and variably penetrant for the thoracic scoliosis phenotype.  The mutation was also detected in additional breeds that were tested, including the American Pitt Bull Terrier, Staffordshire Bull Terrier, Shih Tzu as well as in mixed breed animals, although at lower levels.

Mutations in the DVL1 and DVL3 genes give a very similar phenotype in humans (Robinow syndrome) as that seen with the DVL2 gene mutation seen in the dog. In humans, this includes facial features similar to brachycephaly as seen in dogs.  Thus, it is believed that the DVL2 mutation responsible for curly tail in the dog is also contributing to the brachycephaly that is an additional feature of the curly tail breeds.

For breeds where the screwtail mutation is not fixed, DNA tests are available to identify carrier animals such that the mutation can be eliminated by prudent breeding.  For breeds where the screwtail mutation is fixed, this becomes a welfare issue for the breeds.

Note that the short tail (Bobtail, brachyury) phenotype seen in several dog breeds is caused by a mutation within the unrelated TBXT gene.

References:

OMIA link: [2186-9615]

Niskanen JE, Reunanen V, Salonen M, et al. (2021) Canine DVL2 variant contributes to brachycephalic phenotype and caudal vertebral anomalies. Hum Genet 140:1535-1545. [pm/33599851]

Bertram S, Ter Haar G, De Decker S. (2019) Congenital malformations of the lumbosacral vertebral column are common in neurologically normal French Bulldogs, English Bulldogs, and Pugs, with breed-specific differences. Vet Radiol Ultrasound 60:400-408.  [pm/31050057]

Mansour TA, Lucot K, Konopelski SE, et al. (2018) 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.  [pm/30521570]