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GeneticsGenetics of the Inheritance of Dorsal Ridge and Dermoid Sinus in Rhodesian and Thai Ridgebacks
Summary by Dr. Dominique de Caprona
© de Caprona 2009
The study entitled "Duplication of FGF3, FGF4, FGF 19 and ORAOV1 causes hair ridge and predisposition to dermoid sinus in Ridgeback dogs" by Salmon Hillbertz et al. (2007) finds that the ridges* on the backs of the Thai and Rhodesian Ridgebacks are caused by an autosomal dominant mutation which also predisposes to the congenital disorder named dermoid sinus**.
The dermoid sinus
in dogs resembles the "dermal sinus" condition found in humans. In
the dermoid sinus is located at the beginning and the end of the ridge;
only ridged dogs have the dermoid sinus condition. No ridgeless dogs
dermoid sinus condition have ever been reported.
The authors used the Multiple Ligation Dependent Genome Amplification (MLGA) technique to assess whether the allele for the ridge is associated with a duplication. The results show that ridged Rhodesian and Thai Ridgebacks can be homozygous or heterozygous for a large duplication.
location of the
duplication breakpoints was determined by using interspersed probes in
the critical intervals. The duplication breakpoint between the tandem
was amplified and sequenced using PCR.
it is a dysregulation of the FGF genes expression along the dorsal
which leads to the ridge and a higher risk of dermoid sinus.
I thank L. Andersson and G. Andersson for fine tuning this text and their positive comments.
*Ridges are hairs along the back which are oriented in the opposite direction of those on the rest of the body ending in various crowns resembling cow -licks. They can be found in 3 breeds, the Thai Ridgeback (Thailand) , the Rhodesian Ridegeback (South Africa) and the Phu Quoc dog (Vietnam). Although all 3 breeds have ridges, the ridges themselves look different between the dogs and between the breeds. The AfriCanis of South Africa occasionaly show ridges on their backs as well.
**Dermoid sinus is a genetic skin disorder in dogs. It is a neural tube defect which can appear as single or multiple lumps on the dorsal midline. During normal development, the neural tube from which the spine develops separates from the skin. In the case of a dermoid sinus, this separation is not complete, with the dermoid sinus remaining connected to the animal's spinal cord in some cases, whereas the sinus terminates in a "blind sac" in others. Although the dermoid sinus is more commonly found in ridged breeds, it also occurs occasionally in other breeds such as Chow Chow, Shih Tzu, Yorkshire Terrier, Boxer, Siberian Husky, Golde Retriever and English Springer Spaniel. See this reference
Hillbertz N H C,
Isaksson M, Karlsson E K, Hellmen E, Rosengren Pielberg G, Savolainen
Wad C M, von Euler E, Gustafson U, Hedhammar A, Nilsson M, Lindblad-Toh
K, Andersson L, Andersson G (2007): "Duplication of FGF3, FGF4,
FGF 19 and ORAOV1 causes hair ridge and predisposition to dermoid sinus
in, Ridgeback dogs" in Nature Genetics, Vol. 39, Number 11,