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Polydactyly in a Murgese horse: a case report
Polydactyly in a Murgese Horse: A Case Report F. Giofré, DVM,a V. Caracciolo, engineer,b M. Zanotti, PhD,c M. Polli, PhD, DVM,c and A. M. De Giovanni, PhDd
REFEREED SUMMARY
For the first time, a case of atavic polydactyly is described in a Murgese breed foal born in Calabria, Italy. Cytogenetic analysis has not shown up any abnormality, and neither pedigree study supports the hypothesis of a recessive gene. Polydactyly, in this case, may be attributed to a dominant autosomal gene with incomplete penetrance or to abnormal fetal development due to external causes. INTRODUCTION
Polydactyly is a congenital malformation characterized by the presence of extra toes. This congenital anomaly is fairly common in man, dogs, cats, and sheep and has been described also in horses.1-12 In man it is considered to be a malformation of genetic origin caused by dominant autosomal genes, although some cases may be caused by external factors like exposure to toxins or womb anomalies. Polydactyly can occur isolated or also as a part of a large number of rare inherited and developmental disorders.13 For other species, it has been considered possible that the malformation could be caused by an autosomal dominant gene with incomplete penetrance or by a recessive gene.13 Indeed, some researchers simply refer to polydactyly as an “undefined disease of genetic etiology,” there being little detailed literature concerning the matter. There are ongoing researches into particular candidate genes (eg, Shh gene14 and G1i3 gene15) only in man and mice, which continue to be the most widely studied species. So far, specific genetic research has not been carried out on horses, above all because of the lack
of proven case histories and pedigree data. Evans2 favors the theory of incomplete penetrance of a dominant autosomal gene, while Bowling et al16 refer to trisomy syndrome of the 30th chromosome in 1 particular case. Polydactyly, present since birth, may affect animals of both sexes and of all the breeds. Fedrigo17 classified it as teratologic polydactyly when the extra toe is attached to a normal one or derives from a longitudinal split in the toe and as atavic polydactyly when the extra toe is attached to the normal metacarpal/metatarsal or is accessory to it. Although polydactyly has been known since ancient times, in Italy it was described in horses first by Ercolani,18 De Geronimo,19 Torreggiani,20 and Maccagni21 and later by Martini et al.22 More recently, it has been described in the Giara pony by Lai et al23 and in the Anglo-Arab-Sardo horse by Sanna Passino et al.24,25 From literature it may be seen that in the horse the extra toe is usually situated in the medial face of the anterior limbs and is usually small and badly formed, with an atrophic plantar tip on which the hoof of the horse cannot stand properly.26 MATERIALS AND METHODS
A case of polydactyly in a Murgese foal, born spring 2002 at the Forestry Company Farm (Azienda del Corpo Forestale dello Stato) in Mongiana, Vibo Valentia, Calabria, Italy, has been described. A clinical and radiologic study of the foal has been carried out. Moreover, a study of the pedigree of the affected animal has been done, and a karyotype analysis has been performed according to the method of De Grouchy et al27 with minor modifications. RESULTS
From Provincial Veterinary Service (ASL 8)a and Director of Mongiana Forestry Company,b Vibo Valentia, Calabria, Italy; Institute of Zootechnics, Veterinary Science Facultyc and Agriculture Faculty,d University of Milan, Italy. J Equine Vet Sci 2004;24:248-50. 0737-0806/$ - see front matter © 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jevs.2004.05.003
248
Clinical Description The foal has an extra toe on the rear-medial face of the front left leg protruding from the region of the fetlock (Fig 1) and does not reach the ground. This extra skincovered toe is very small and stumpy. There is the outline of a cone-shaped hoof, however, with no plantar surface
Journal of Equine Veterinary Science
June 2004
Figure 1. Murgese foal with polydactyly. (Forestry Company Farm: Mongiana,Vibo Valentia, Calabria, Italy)
Figure 3. Radiograph examination supernumerary toe. (Forestry Company Farm: Mongiana, Vibo Valentia, Calabria, Italy)
highly developed internal accessory metacarpal bone squashed against the main metacarpus and distally articulated with the extra toe (Fig 3). Thus, the overall clinical and radiologic situation led us to believe that the horse was affected by atavic polydactyly similar to that noted in the Giara pony by Lai et al23 and by Sanna Passino et al.25
Genetic Analysis
Figure 2. Supernumerary toe. (Forestry Company Farm: Mongiana,Vibo Valentia, Calabria, Italy)
(Fig 2). Clinical examination of the horse, otherwise in excellent health, showed a slight contracture of the tendons flessori in the same limb. Radiography revealed a
Volume 24, Number 6
From research carried out in the geographic region of origin and with the breed association, it appears that no other case of polydactyly has ever been noted in the Murgese horse. The pedigree of the studied foal was examined back to the fourth generation, since further analysis was not possible owing to missing genealogic data. Although the Murgese breed has a small population size, in the 4 considered generations there were no common ancestors, which could support the hypothesis of a reces-
249
sive autosomal gene. No cytogenetic abnormality was found in the foal and in its parents. DISCUSSION
Malformations are defined as alterations of the normal anatomic and/or functional structure of an organ or apparatus, which can occur in the embryonic period and are thus termed congenital. Anomalies of this type derive from alterations in the normal processes of differentiation and/or growth of various structures during organogenesis and development. Congenital malformations can be determined by endogenous factors, such as mutated genes transmitted with Mendelian inheritance, or by exogenous factors like developmental conditions or toxins during the embryonic or fetal life. As no cases of polydactyly have been noted in the Murgese breed in the past and considering that pedigree analysis has not shown ancestors with evident polydactyly and inbreeding, we can suppose that the abnormality is not due to the presence of recessive autosomal genes. Neither can the malformation be attributed to a chromosome abnormality of the type described by Bowling et al,16 since both the foal and its parents were cytogenetically normal. Therefore, we can only conclude that it is probably a characteristic caused by incomplete penetrance of a dominant autosomal gene, as reported by Evans et al,2 or simply a spontaneous, not inherited anomaly in fetal development due to (nongenetic) exogenous causes. To prove if polydactyly present in this case is a malformation due to genetic rather than exogenous factors, it would be helpful to mate the horse under examination and study its offspring as well as the descendants of other reported cases. We believe that the animals affected by this malformation should not be rejected but should be used in planned matings to verify if polydactyly in horses is an abnormality of genetic or environmental origin.
3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.
REFERENCES 1. 2.
250
Drahan OV. Die Polydaktylie des Pferdes. Berl Tierarztl Wschr 1921;37:75. Evans LH, Jenny J, Raker OW. Surgical correction of polydactilism in the horse. J Am Vet Med Assoc 1965;146:1405-8.
26. 27.
Leipold NW, MacDonald KR. Adactylia and polydactylia in a Welsh foal. Vet Med Small Anim Olin 1971;66:928-30. McGavin MD, Leipold NW. Attempted surgical correction of equine polydactylism. J Am Vet Med Assoc 1975;166:63-4. Lose MP. A supernumerary leg in a thoroughbred filly foal. Vet Med Small Anim Olin 1978;73:1071. Flehrens E, Donawick WJ, Raker OW. Polydactylism in a foal. J Am Vet Med Assoc 1979;174:266-8. Dore MA. Teratogenic polydactyly in a halfbred foal. Vet Rec 1989;125:375-6. Barber SM. Unusual polydactylism in a foal: a case report. Vet Surg 1990;19:203-7. Frew DG, Wright IM. Supernumerary digits in the horse. Equine Pract 1990;12:21-6. Delaunay A, Le Nihouannen JO. A propos d’un cas de didactylie chez una puliche. PVE 1995;27:237. Weinhart G, Gotz E, Gotz NJ. Polydactyly in a foal: a case report. Tlerarztl Praxis 1996;24:275-7. Briot. Em fall von polydaktylie bei einem und zwar bei Mustang Pferde aus den Prarien Sudamenkas. Jahresbericht uber die Leistungen auf dem Gebiete der Veterinar-Medicin 1898:169. Crowe MW. Equine congenital defects. Am J Vet Res 1985;46: 353-8. Clark RN, Marker PC, Kingsley DM. A novel candidate gene for mouse and human preaxial polydactily with altered expression in limbs of Hemimelic extra-toes mutant mice. Genomics 2000;67:19-27. Thien H, Ruther U. The mouse mutation Pdn (polydactyly nagoya) is caused by the integration of a retrotransposon into the G1i3 gene. Mammalian Genome 1999;10:205-9. Bowling AT, Milion LV. Two autosomal trisomies in the horse: 64,XX,26,+t(26q26q) and 65,XX,+30. Genome 1990;33:679-82. Fedrigo G. Sopra un caso di polidattilia ipo-microfalangica in un cavallo. La Clinics Veterinaria 1943;21:183-8. Ercolani GB. Delia polidattilia e della polimelia nell’uomo e nei mammiferi. Mem Accad Scient Bologna 1882. De Geronimo N. Piedi didattili negli equini. Giornale Vet Miiitare 1891:25-7. Torreggiani G. Di un magnifico caso di polidattilismo in un cavallo. Gior Reg Soc Acc Vet It 1898:506-8. Maccagni G. Poiidattilia in un puledro. Nuovo Ercol. 1901;5:192-4. Martini E, Sagri PD. Osservazioni anatoiniche su di un caso di polidattilia anteriore e posteriore destra in Equus caballus. La Nuova Veterinaria 1963;39:337-43. Lai P, Cancedda M, Pinna W. Polidattilia in Un cavallino della Giara. Atti SIS Vet 1988;42:1435-7. Sanna Passino E, Serra GB, Careddu GM, Muzzetto P. Su Un case di polidattilia in un cavallo anglo-arabo-sardo. V˚ Convegno SICV, Ostuni, Italy 11-12 Giugno 1998:210-3. Sanna Passino E, Careddu GM, Manunta ML, Muzzetto P. La polidattilia nel cavallo: tara o ritorno atavico? Veterinaria Pratica Equina 2002;4:33-7. Mensa A. Podologia—UTET Torino, Italy, 1950. De Grouchy J, Roubin M, Passage E. Microtechnique pour 1’ etude des chromosomes humains a partir d’une culture de leucocytes sangulns. Ann Génét 1964;7:45-6.
Journal of Equine Veterinary Science
June 2004
REFEREED SUMMARY
For the first time, a case of atavic polydactyly is described in a Murgese breed foal born in Calabria, Italy. Cytogenetic analysis has not shown up any abnormality, and neither pedigree study supports the hypothesis of a recessive gene. Polydactyly, in this case, may be attributed to a dominant autosomal gene with incomplete penetrance or to abnormal fetal development due to external causes. INTRODUCTION
Polydactyly is a congenital malformation characterized by the presence of extra toes. This congenital anomaly is fairly common in man, dogs, cats, and sheep and has been described also in horses.1-12 In man it is considered to be a malformation of genetic origin caused by dominant autosomal genes, although some cases may be caused by external factors like exposure to toxins or womb anomalies. Polydactyly can occur isolated or also as a part of a large number of rare inherited and developmental disorders.13 For other species, it has been considered possible that the malformation could be caused by an autosomal dominant gene with incomplete penetrance or by a recessive gene.13 Indeed, some researchers simply refer to polydactyly as an “undefined disease of genetic etiology,” there being little detailed literature concerning the matter. There are ongoing researches into particular candidate genes (eg, Shh gene14 and G1i3 gene15) only in man and mice, which continue to be the most widely studied species. So far, specific genetic research has not been carried out on horses, above all because of the lack
of proven case histories and pedigree data. Evans2 favors the theory of incomplete penetrance of a dominant autosomal gene, while Bowling et al16 refer to trisomy syndrome of the 30th chromosome in 1 particular case. Polydactyly, present since birth, may affect animals of both sexes and of all the breeds. Fedrigo17 classified it as teratologic polydactyly when the extra toe is attached to a normal one or derives from a longitudinal split in the toe and as atavic polydactyly when the extra toe is attached to the normal metacarpal/metatarsal or is accessory to it. Although polydactyly has been known since ancient times, in Italy it was described in horses first by Ercolani,18 De Geronimo,19 Torreggiani,20 and Maccagni21 and later by Martini et al.22 More recently, it has been described in the Giara pony by Lai et al23 and in the Anglo-Arab-Sardo horse by Sanna Passino et al.24,25 From literature it may be seen that in the horse the extra toe is usually situated in the medial face of the anterior limbs and is usually small and badly formed, with an atrophic plantar tip on which the hoof of the horse cannot stand properly.26 MATERIALS AND METHODS
A case of polydactyly in a Murgese foal, born spring 2002 at the Forestry Company Farm (Azienda del Corpo Forestale dello Stato) in Mongiana, Vibo Valentia, Calabria, Italy, has been described. A clinical and radiologic study of the foal has been carried out. Moreover, a study of the pedigree of the affected animal has been done, and a karyotype analysis has been performed according to the method of De Grouchy et al27 with minor modifications. RESULTS
From Provincial Veterinary Service (ASL 8)a and Director of Mongiana Forestry Company,b Vibo Valentia, Calabria, Italy; Institute of Zootechnics, Veterinary Science Facultyc and Agriculture Faculty,d University of Milan, Italy. J Equine Vet Sci 2004;24:248-50. 0737-0806/$ - see front matter © 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jevs.2004.05.003
248
Clinical Description The foal has an extra toe on the rear-medial face of the front left leg protruding from the region of the fetlock (Fig 1) and does not reach the ground. This extra skincovered toe is very small and stumpy. There is the outline of a cone-shaped hoof, however, with no plantar surface
Journal of Equine Veterinary Science
June 2004
Figure 1. Murgese foal with polydactyly. (Forestry Company Farm: Mongiana,Vibo Valentia, Calabria, Italy)
Figure 3. Radiograph examination supernumerary toe. (Forestry Company Farm: Mongiana, Vibo Valentia, Calabria, Italy)
highly developed internal accessory metacarpal bone squashed against the main metacarpus and distally articulated with the extra toe (Fig 3). Thus, the overall clinical and radiologic situation led us to believe that the horse was affected by atavic polydactyly similar to that noted in the Giara pony by Lai et al23 and by Sanna Passino et al.25
Genetic Analysis
Figure 2. Supernumerary toe. (Forestry Company Farm: Mongiana,Vibo Valentia, Calabria, Italy)
(Fig 2). Clinical examination of the horse, otherwise in excellent health, showed a slight contracture of the tendons flessori in the same limb. Radiography revealed a
Volume 24, Number 6
From research carried out in the geographic region of origin and with the breed association, it appears that no other case of polydactyly has ever been noted in the Murgese horse. The pedigree of the studied foal was examined back to the fourth generation, since further analysis was not possible owing to missing genealogic data. Although the Murgese breed has a small population size, in the 4 considered generations there were no common ancestors, which could support the hypothesis of a reces-
249
sive autosomal gene. No cytogenetic abnormality was found in the foal and in its parents. DISCUSSION
Malformations are defined as alterations of the normal anatomic and/or functional structure of an organ or apparatus, which can occur in the embryonic period and are thus termed congenital. Anomalies of this type derive from alterations in the normal processes of differentiation and/or growth of various structures during organogenesis and development. Congenital malformations can be determined by endogenous factors, such as mutated genes transmitted with Mendelian inheritance, or by exogenous factors like developmental conditions or toxins during the embryonic or fetal life. As no cases of polydactyly have been noted in the Murgese breed in the past and considering that pedigree analysis has not shown ancestors with evident polydactyly and inbreeding, we can suppose that the abnormality is not due to the presence of recessive autosomal genes. Neither can the malformation be attributed to a chromosome abnormality of the type described by Bowling et al,16 since both the foal and its parents were cytogenetically normal. Therefore, we can only conclude that it is probably a characteristic caused by incomplete penetrance of a dominant autosomal gene, as reported by Evans et al,2 or simply a spontaneous, not inherited anomaly in fetal development due to (nongenetic) exogenous causes. To prove if polydactyly present in this case is a malformation due to genetic rather than exogenous factors, it would be helpful to mate the horse under examination and study its offspring as well as the descendants of other reported cases. We believe that the animals affected by this malformation should not be rejected but should be used in planned matings to verify if polydactyly in horses is an abnormality of genetic or environmental origin.
3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.
REFERENCES 1. 2.
250
Drahan OV. Die Polydaktylie des Pferdes. Berl Tierarztl Wschr 1921;37:75. Evans LH, Jenny J, Raker OW. Surgical correction of polydactilism in the horse. J Am Vet Med Assoc 1965;146:1405-8.
26. 27.
Leipold NW, MacDonald KR. Adactylia and polydactylia in a Welsh foal. Vet Med Small Anim Olin 1971;66:928-30. McGavin MD, Leipold NW. Attempted surgical correction of equine polydactylism. J Am Vet Med Assoc 1975;166:63-4. Lose MP. A supernumerary leg in a thoroughbred filly foal. Vet Med Small Anim Olin 1978;73:1071. Flehrens E, Donawick WJ, Raker OW. Polydactylism in a foal. J Am Vet Med Assoc 1979;174:266-8. Dore MA. Teratogenic polydactyly in a halfbred foal. Vet Rec 1989;125:375-6. Barber SM. Unusual polydactylism in a foal: a case report. Vet Surg 1990;19:203-7. Frew DG, Wright IM. Supernumerary digits in the horse. Equine Pract 1990;12:21-6. Delaunay A, Le Nihouannen JO. A propos d’un cas de didactylie chez una puliche. PVE 1995;27:237. Weinhart G, Gotz E, Gotz NJ. Polydactyly in a foal: a case report. Tlerarztl Praxis 1996;24:275-7. Briot. Em fall von polydaktylie bei einem und zwar bei Mustang Pferde aus den Prarien Sudamenkas. Jahresbericht uber die Leistungen auf dem Gebiete der Veterinar-Medicin 1898:169. Crowe MW. Equine congenital defects. Am J Vet Res 1985;46: 353-8. Clark RN, Marker PC, Kingsley DM. A novel candidate gene for mouse and human preaxial polydactily with altered expression in limbs of Hemimelic extra-toes mutant mice. Genomics 2000;67:19-27. Thien H, Ruther U. The mouse mutation Pdn (polydactyly nagoya) is caused by the integration of a retrotransposon into the G1i3 gene. Mammalian Genome 1999;10:205-9. Bowling AT, Milion LV. Two autosomal trisomies in the horse: 64,XX,26,+t(26q26q) and 65,XX,+30. Genome 1990;33:679-82. Fedrigo G. Sopra un caso di polidattilia ipo-microfalangica in un cavallo. La Clinics Veterinaria 1943;21:183-8. Ercolani GB. Delia polidattilia e della polimelia nell’uomo e nei mammiferi. Mem Accad Scient Bologna 1882. De Geronimo N. Piedi didattili negli equini. Giornale Vet Miiitare 1891:25-7. Torreggiani G. Di un magnifico caso di polidattilismo in un cavallo. Gior Reg Soc Acc Vet It 1898:506-8. Maccagni G. Poiidattilia in un puledro. Nuovo Ercol. 1901;5:192-4. Martini E, Sagri PD. Osservazioni anatoiniche su di un caso di polidattilia anteriore e posteriore destra in Equus caballus. La Nuova Veterinaria 1963;39:337-43. Lai P, Cancedda M, Pinna W. Polidattilia in Un cavallino della Giara. Atti SIS Vet 1988;42:1435-7. Sanna Passino E, Serra GB, Careddu GM, Muzzetto P. Su Un case di polidattilia in un cavallo anglo-arabo-sardo. V˚ Convegno SICV, Ostuni, Italy 11-12 Giugno 1998:210-3. Sanna Passino E, Careddu GM, Manunta ML, Muzzetto P. La polidattilia nel cavallo: tara o ritorno atavico? Veterinaria Pratica Equina 2002;4:33-7. Mensa A. Podologia—UTET Torino, Italy, 1950. De Grouchy J, Roubin M, Passage E. Microtechnique pour 1’ etude des chromosomes humains a partir d’une culture de leucocytes sangulns. Ann Génét 1964;7:45-6.
Journal of Equine Veterinary Science
June 2004