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Study on Hair Abnormalities of Curly Coated Retrievers

Excess Keratin Protein, Pigment Clumping and Eccentric Hair Shaft Locations found in Test Dogs

Image Copyright Ross Bond 2017

This curly exhibits hair loss on the sternum.

Study: Excessive Keratin, Pigment Clumping, and Hair Shaft Anomalies Found in Curly Coated Retrievers With Hair Loss


A study of hair loss in Curly Coated Retrievers reveals affected curlies commonly have too much Keratin in the upper part of their hair follicles, low-grade pigment clumping, and subtle telogenisation of hair follicles.


In clinical examination and testing of 14 Curly Coated Retrievers with symmetrical, non-pruritic hair loss and thinning and other types of coat changes, researchers determined the hair follicle dysplasia in Curly Coated Retrievers was similar to that of Irish water spaniels and Chesapeake Bay retrievers but distinct from the follicular dysplasia found in Portuguese water dogs.


Included in the study were 11 black and 3 liver curlies from the UK and Sweden, ranging in age from 2 to 9 years. The sampling included males and females.


Almost all tissue samples (28 of 30) examined showed infundibular hyperkeratosis. The infundibulum is the upper portion of a hair follicle. This area is lined by Keratin producing layers of cells.  In hyperkeratosis, too much Keratin accumulates in the follicle.


“Affected CCRs commonly have too much keratin here (the hair follicle cavity), although routinely the follicles are not obviously dilated (but that does occur in some other diseases with that feature, for example spaniels with ‘seborrhoea’),” said Dr. Ross Bond, of the Royal Veterinary College in England.*


Keratin is a protein found in hair, skin, nails, hoofs and horns. Keratin fiber bundles are one of the primary components of hair and the outer layers of skin—essentially the ‘building blocks’ of hair and nails. This protein is part of the process of hair growth in the hair follicle.


What is clear from the study is hair loss in curlies is NOT caused by skin diseases of hypothyroidism (underactive thyroid gland) or hyperadrenocorticism (Cushing’s Disease).


“These dogs are NOT hypothyroid,” Bond said, speaking of the 14 dogs clinically examined and tested.


Some affected curlies also exhibited some hair shaft anomalies, including distorted anagen bulbs (10 dogs) and transverse fractures (8 dogs).  Anagen bulbs are those connected to the hair shaft in the growth stages.


Hair shaft abnormalities included bulges, notches, and fractures--abnormalities which can lead to hairs breaking off. However, those anomalies only occurred in 8 dogs and the researchers concluded the anomalies were not a prominent feature in the 14 dogs they studied.  


More significant, according to the study, is increased telogenisation of the hair follicles in the areas of hair loss. 


“Our data indicates that telogenisation must also be regarded as a contributing factor for alopecia in CCRs, as an increase in the percentage of follicles in telogen leads to increased hair shedding (Trueb 2008),” the study’s authors write.


Telogenisation is the change of hair follicles from the growth stage to the resting stage.  Hair remains in the hair follicle during this resting or dormant stage but fewer anagen stage follicles and more telogen follicles means less new hair growth. Hair follicles are in different stages—some in growth stages (anagen), some in a transition stage (catagen), some in a resting stage (telogen) and some in a shedding stage. Breeds differ in how long these stages last. Some breeds’ anagen stages last longer and they maintain a longer period of hair growth resulting in longer coats.


Location of the hair shaft in the follicle cavity was eccentric in 11 of 30 skin sections taken from affected areas. In an earlier study of healthy beagles, there were no eccentric hair shaft locations in 35 skin samples. More study is needed to determine whether these hair shaft locations are unique to the curly or whether other curly haired dogs with alopecia also display eccentric shaft locations.


It appears the alopecia in Curly Coated Retrievers is similar to, but not identical with, that in Irish water spaniels and Chesapeake Bay retrievers.


Both affected CCRs and affected chessies exhibit infundibular hyperkeratosis (excess Keratin in hair follicles) and pigment clumping, but Chesapeake Bay retrievers do not have neck hair loss or frizzy coat changes. Hair loss occurs at a younger age and waxes and wanes more often in curly coated retrievers.


Believed to be genetic in basis, the researchers did not identify any effective therapy for the coat abnormalities found in curlies.


Researchers will continue their search for the molecular and genetic basis of the curly baldness abnormalities.


Dr. Bond indicated is forwarding the DNA samples collected in this study to Dr. Tosso Leeb at the University of Bern’s Institute of Genetics for inclusion in research on hereditary skin diseases, including follicular dysplasia in curlies.


Information for this article was obtained from email correspondence with Dr. Bond and the report.


The report is titled:

Clinical and pathological features of hair coat abnormalities in curly coated retrievers from UK and Sweden


Authors: R. Bond, K. Varjonen, A. Hendricks, Y. M. Chang, and H. Brooks Brownlie


Journal of Small Animal Practice (2016), 57, 659-667

Copyright 2016 British Small Animal Veterinary Association

Curlies are actually a double-coated breed. Read about it


Despite what you might have heard in the past,

Curly coated retrievers are actually a double-coated breed. 

University of Bern genetic researcher Dr. Tasso Leeb is still looking for samples from coat patterned curly coated retrievers.

Areas of Follicular Dysplasia in a test colony of curlyc coated retrievers.
Illustration J. Marti 2017
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