Australian Shepherds

Pelger-Huet syndrome anomaly and merle genetics

History of Pelger-Huet Anomaly

  • abnormality in morphology in white blood cells was first discovered by Pelger in 1928, when studying blood of tuberculosis patients
  • Huet found similar morphology in his patients in 1932 and hypothesized that it was genetically linked
  • Huet confirmed it was linked to genetics and not to tuberculosis, also that the abnormality was benign
  • The term for this abnormality was changed from Pelger anomaly to Pelger-Huet anomaly

Pelger-Huet: Who is affected? What is affected?

  • Affects: Humans, Rabbits, Cats, Dogs, Horses, and Mice
  • Affects other breeds: Cocker Spanials, Basenji's, Border Collie's, etc.
  • Occurs approximately 9.8% in Australian Shepherds
  • Affects white blood cells

mode of inheritance, diagnosis, and prognosis

  • Autosomal dominant, incomplete penetrance
  • It can be congenital or pseudo (acquired via disease/ infection)
  • Benign for heterozygous; lethal for homozygous (reabsorbed in Utero)
  • Morphological differences between Hetero and Homozygous P-H anomaly were discovered in rabbits
  • Homozygous is incredibly rare in dogs, but few cases suggest it can lead to skeletal deformities (known cases in Samoyed breed)
  • Phenotypic in the blood, affecting granulocytes; PHA changes the morphology in Neutrophils (white blood cells)
  • Nuclei of Neutrophils are hyposegmented and bilobed
  • Can be tested using blood smears and staining

Pelger-Huet anomaly affects

  • Misconception: P-H was believed to be linked to, associated with, or misdiagnosed as: chronic infection, preleukemic syndrome, inflammation or infection, or drug-induced chances in leucocyte's, left shift ( increase in immature white blood cells, typically an indicator of inflammation or infection)
  • Neutrophils with P-H are still functional and effective against bacterial infections
  • There is no relation between P-H and risk of disease/ infection
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Merle gene- What is Merle? Mode of inheritance?

  • Standard merle (Mm): a intermingled mixture of diluted and normal pigments
  • Merle dogs can commonly have blue irisis or be heterochromic
  • Double merle (MM): predominantly white
  • Inherited autosomal, incomplete dominance
  • Two locus: Merle (M) and Separate Harlequin (S)
Merle (dog coat) - Video Learning -

How are Shepherds affected?

  • Double merle (aka merle syndrome) can lead to deformities
  • Double merle can impaire auditory (deafness) and optic systems
  • Microphthalmia- one or both eyeballs look small
  • Coloboma- a hole in structure of eye
  • Similar to Waardenburg syndrome in humans
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Merle Syndrome testing and prevention

  • Merle parent can produce non-merle offspring
  • Tests can be run for cryptic, and probability calculations for merle vs non-merle offspring
  • Can prevent via testing and improved breeding methods


  • Clark, Leigh Ann, Jacquelyn M. Wahl, Christine A. Rees, and Keith E. Murphy. 2005. Retrotransposon insertion in SILV is responsible for merle patterning of the domestic dog. Proceedings of the National Academy of Sciences of the United States of America. 103(5). 1376-1381. Doi:10.1073.

  • Cunningham, John M. , Mrinal M. Patnaik, Dale E. Hammerschmidt, and Gregory M. Vercellotti. 2009. Historical perspective and clinical implications of the Pelger-Huet cell. American Journal of Hematology. 84.116-119. Doi: 10.1002.

  • Hédan, Benoit, Sébastien Corre, Christophe Hitte, Stéphane Dréano, Thierry Vilboux, Thomas Derrien, Bernard Denis, Francis Galibert, Marie-Dominque Galibert, and Catherine André. 2006. Coat Color in Dogs: Identification of the Merle locus in the Australian Shepherd breed. BMC Veterinary research. 2(9). Doi: 10.1186.

  • Latimer, K.S, R.P Campagnoli, and D.M Danilenko. 2000. Pelger–Hue¨t Anomaly in Australian Shepherds: 87 Cases (1991–1997). Comparative Haematology International. 2010(1). 9-13. Doi: 10.1007.

  • Vale, André M. , Klívio Loreno R. Tomaz, Rejane S. Sousa, and Benito Soto-Blanco. 2011. Pelger-Huët anomaly in two related mixed-breed dogs. Journal of Veterinary Diagnostic Investigation. 23(4). 863-865. DOI: 10.1177.