Dermoid Sinus - A Summary by
E. Clough, V.M.D.
1010 Daniel Webster Highway
Merrimack, New Hampshire 03054
***Update: 12/4/09:Nature Genetics 39, 1318 - 1320 (2007)
Published online: 30 September 2007 | doi:10.1038/ng.2007.4
Duplication of FGF3, FGF4, FGF19 and ORAOV1 causes hair ridge and predisposition to dermoid sinus in Ridgeback dogs
Nicolette H C Salmon Hillbertz1,
Magnus Isaksson2,
Elinor K Karlsson3,4,
Eva Hellmén2,5,
Gerli Rosengren Pielberg6,
Peter Savolainen7,
Claire M Wade3,8,
Henrik von Euler9,
Ulla Gustafson1,
Åke Hedhammar9,
Mats Nilsson2,
Kerstin Lindblad-Toh3,6,
Leif Andersson1,6
&
Göran Andersson1
The
dorsal hair ridge in Rhodesian and Thai Ridgeback dogs is caused by a
dominant mutation that also predisposes to the congenital developmental
disorder dermoid sinus. Here we show that the causative mutation is a
133-kb duplication involving three fibroblast growth factor (FGF)
genes. FGFs play a crucial role in development, suggesting that the
ridge and dermoid sinus are caused by dysregulation of one or more of
the three FGF genes during development.
INTRODUCTION:
Dermoid sinus (D.S.) was first used to describe the Rhodesian Ridgeback
skin anomaly by Steyn, et al. This skin condition has also been called
trichiasis spiralis, dermoid cyst, dermoid inclusion cyst and epidermal
inclusion cyst. All of these terms have some applications; however,
Dermoid, skin-like sinus, channel or fistula; (cyst means sac, i.e.,
not open to the surface) is most applicable. The Rhodesian Ridgeback
Club of the U.S., Inc. prefers to use D.S. to describe the condition.
DESCRIPTION:
No reports have been located which substantiate the author's impression
that D.S. has been found in other breeds.(Ed. Notes: DS are also found
it in the Thai Ridgeback.) Dermoid sinus included in the ridge has been
reported only once. They also occur in the sacral (rump) area and in
this location are sometimes connected to the dura (spinal cord
covering). This is not the case in the more common cervical (neck area)
D.S. which connects the skin to the dorsal spinous ligament (the
ligament which connects the top parts of the vertebrae). One or more
D.S. may occur in the same animal. These sinuses are congenital
(present at birth) and can be palpated (felt) as cords running between
the skin and the spine. They form a small external opening which can be
readily seen once the hair has been shaved.
Histologically (microscopically) the sinus is a thick-walled tube
composed chiefly of fibrous tissue and lined with stratified squamous
epithelium (skin cells). The surrounding connective tissue may or may
not contain hair follicles, sebaceous glands and sweat glands which
open into the lumen (hollow center) of the sinus. In uncomplicated
cases the sinus is filled with sebum (oil), skin debris and hair. Once
infected with bacteria the resulting inflammation and abscessation can
lead to myelitis and encephalitis (swelling and infection of the spinal
cord, its covering, and the brain). The reason for discrimination
against animals with D.S. is the almost inevitable abscess, which
forms.
HERITABILITY:
Although not well understood, transmission of D.S. seems to be a
dominant, polygenic problem with inconstant penetration. Another
geneticist thinks that D.S. is due to a single completely recessive
autosomal gene. This is not likely because normal parents do produce
pups affected with D.S. Because of the genetic complexity and the
difficulty in arranging, coordinating and collating the breeding
studies necessary to prove the heredity of D.S., it is unlikely that we
will be able to substantiate the exact mechanism of genetic
transmission. There is a widely held belief that breeding Ridgebacks
with D.S. produces an increased prevalence of pups with D.S. The R.R.
Club of the U.S., Inc. believes that this could be substantiated if
breeders had accurate records which could be collated and computed. It
is our belief that careful controlled breeding studies would prove the
inheritance of D.S. to be not only complex but also inter-related with
other characteristics. Therefore, the likelihood seems to be remote
that we will ever have Ridgebacks which are entirely free of D.S.
Because selective breeding will unquestionably reduce the prevalence of
D.S., but probably not eliminate its occurrence, and because the
condition results in difficult to treat abscesses unless surgically
removed, it is our opinion and strong recommendation that dogs which
have D.S. not be acceptable as show or breeding candidates. Surgical
correction can be accomplished; however, culling at birth is a more
humane way to handle the affected pups.
References
1.Antin, I.P.: Dermoid Sinus in a Rhodesian Ridgeback Dog.
J.A.V.M.A., Vol. 157 No. 7, (1970):
961. 2.Burns, M. and M.N.Fraser: Genetics of the Dog.
J.B.Lippincott Co., Philadelphia PA
(1966): 84. 3.Hawley, T.C.: The Rhodesian Ridgeback
Craft Press, Pretoria, S.A., (1957):
53. 4.Hofmeyr, C.F.B.: Dermoid Sinus in the Ridgeback
Dog J.Small Animal Practice., Vol. 4.
Suppl. (1957): 5-8.
5.Lord, L.H.; A.J.Cawley and J.Gilray: Mid-Dorsal Dermoid
Sinuses in Rhodesian Ridgeback Dogs - A Case Report. J.A.V.M.A.,
131 (1957): 515-518 6.Lutman, F.C.: How
to Raise and Train a Rhodesian Ridgeback. T.F.H. Publications,
Jersey City, NJ (1966). 7.Personal communications
from numerous Rhodesian Ridgeback friends. 8.Severin, G.A.:
Inheritable and Congenital Diseases in Dogs. Dog World
(December 1974). 9.Steyn, H.P. J. Quinlan and C. Jackson: A skin Condition seen in Rhodesian
Ridgeback Dogs: Report on two cases. J.S.A.V.M.A. X(4), (1939): 170-174.