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| DEFINITION: CRYPTORCHIDISM:
Greek derivation; Hidden
testicle. Cryptorchidism is a condition affecting the dog in which one or both testicles do not fully descend into the scrotum. The condition may be presented in two forms: 1.) Unilateral cryptorchidism refers to the normal descent of a singular testis. 2.) Bilateral cryptorchidism results in the retention of both testes. . Cryptochidism is the absence of testicles due to retention in the abdomen or inguinal region. It can be either one (uni-) or both (bi-lateral) testicles, or even may slide in and out of the scrotum. In Greek, kryptos means hidden, secret, or covered, and orchi- is a combining form referring to the testicles. Monorchidism, on the other hand, is a total absence of one testicle, while anorchidism is the total absence of both testicles, both of which are very rare. . Cryptorchid testicles may be retained within the abdominal cavity, or partially descend into a subcutaneous (under the skin) position in the inguinal area. Diagnosis of cryptorchidism is straightforward and based on physical examination. A subcutaneous testicle can usually be palpated, but this is not true for one which is retained within the abdomen. Most cases are unilaterally cryptorchid, and the right testicle is twice as likely to be retained as the left. . Embryologically, the testes start life near the developing kidney. As the embryo grows, the kidneys are held up near the spine, but the testes move towards the tail and belly passively until they reach the inguinal canal - the entrance to the scrotum. A cord called the gubernaculum descends into the scrotum. As the gubernaculum swells it enlarges the inguinal canal, it also becomes softer and less resistant so that the testicle can compress it rather than bouncing off it. The testicle continues to descend passively, the gubernaculum stretching the inguinal canal and then receding back away from the descending gland. This process normally occurs in the first 3-4 days of life, but the testis reaches its final scrotal location about the fifth week. The swelling, elongation and regression of the gubernaculum is governed by the release of testosterone, the testicular hormone. Various problems could prevent this descent. If the testis is too large, and/or the inguinal ring too tight the testis won't pass through. However, if the inguinal ring is too loose the testicle could pop back into the inguinal canal, which is often thought to be the cause of the problem in Yorkies. Defects in the gubernaculum or anatomical folds could also prevent normal development. . Research has shown that cryptorchidism greatly increases by up to ten times the dog's risk of testicular cancer and torsion. Sertoli cell tumors and seminomas are tumors commonly seen in cryptorchid dogs. Testicular torsion is a twisting of the testicle's blood supply, resulting in tremendous pain and swelling, literally overnight the testicle can swell to about the size of a small cantaloupe. . Due to the thermal suppression of spermatogenesis, bilateral cryptorchids are sterile while unilateral cryptorchids are usually fertile. Cryptorchidism is estimated to exist in 6-8% of the canine population (Canine and Feline Endocrinology and Reproduction, Feldman and Nelson). Saint Bernards are noted as a breed at risk. An additional phenomenon, monorchidism, may occur in very few dogs. Monorchidism is a rare condition in which only one testis actually develops in the dog's body. Confirmation of monorchidism may only be determined via plasma testosterone analysis. The concentration of plasma testosterone is significantly lower in dogs who lack one or both testes. Unlike unilateral cryptorchidism, the testis is not ectopic but rather, does not exist in any location. . HERITABILITY: Cryptorchidism is a congenital anomaly which is described as a sex limited (occurs only in males) trait. The incidence of cryptorchidism is greatly higher in that of pure-bred dogs and specifically, in that of heavily line-bred animals. Bilateral retention is reported to be most common in in-bred animals (Vet. Clinics of North America: Small Animal Practice-Vol. 21, No. 3, May 1991). The dam and sire of the cryptorchid pup may appear to be normal while being carriers for the defect. Given the polygenic nature of cryptorchidism, it is difficult to calculate quantitative results with respect to frequency and distribution. Simple recessives provide statistical expectations as we consider a limited number of possibilities yet polygenic modes of inheritance are far more complicated as a singular gene may be responsible for but one aspect of an entire process in which several genes dictate the completion of the event ie: descent of the testes. With this in mind, it is not difficult to understand how an affected (cryptorchid) animal may produce seemingly normal offspring. . Testicular descent involves a seemingly simple process of moving from one location within the abdomen, to another. The mechanism by which descent is achieved however (contractions of abdominal muscles as well as intra-abdominal pressure), is considerably more complicated. Central to proper development and subsequent descent of the testes, is an intricate yet undetermined interplay of androgenic hormones, non-androgenic secretions and genetic predisposition. . Current research provides that it is probable that multiple genes are responsible for the condition of cryptorchidism. Unfortunately, our knowledge of the specific nature or cause for undescended testes is limited to studies involving adult men and pigs; conclusions which are not necessarily applicable to dogs. Hormonal analysis has eliminated hormones as being the sole cause for a failure in descent. Rather, nonandrogenic factors which determine gubernacular outgrowth are thought to be contributory. . COMPLICATIONS: The ectopic testis is prone to a variety of complications including testicular torsion and neoplasm. Tumors may also occur in fully descended testes, however most develop at the site of the undescended testis. Tumors are classified by their histologic appearance. 1.) Sertoli cell tumors tend to be relatively small in size and rarely exhibit invasive behavior. Enlargement of the tumor, however, may result in hemorrhage and necrosis of local tissue. 2.) Seminomas will metastasize, spreading to surrounding lymphatic sites and the abdominal viscera. In addition, seminomas have been linked to symptoms which occur as a consequence of improper hormone levels. Ex: Alopecia, prostate disease and pendulous penile sheath. . It is not important that I detail the various tumors. It is important to understand that the majority of tumors occur in the cryptorchid male, at the site of the undescended testis. For this reason, an orchiotomy (removal of the testis) is recommended. . ESTABLISHING CARRIERS: A study involving Beagles revealed that 40 offspring from a single dam were needed in order to establish the dam as a carrier. Cryptorchidism, therefore, is extremely difficult to control once it is within a population. Establishing carriers is most tedious. Given these facts, we are inclined to throw up our hands and proclaim defeat. After all, we are seldom used to a good and challenging race; a race which, in the end, we may have to begin over again. Fortunately, we are encouraged by results which reveal substantive improvements in agriculture. . Thirty years of artificial selection have resulted in myriad improvements ranging from increased egg and milk production to a reduction of cryptorchidism in commercial livestock. Sheep provide an excellent example of how we might control cryptorchidism within a population of animals. . By removing all cryptorchids (affected males) from their breeding programs, sheep farmers experienced a 18-28% decrease in the incidence of cryptorchidism. Their startling results were not based on complicated permutations with regard to possible "carriers" They employed the best of all common sense by focusing on the obvious; eliminating from their breeding programs, animals with one or no descended testicles. Frankly, it doesn't get much easier. . Commercial viability dictates that breeders of these animals place such emphasis on reproductive failures. After all, they cannot *afford* to risk infertility. Affected animals were systematically removed from the breeding population thereby reducing the incidence of cryptorchidism. . FINAL SELECTION: The frequency with which undesirable alleles appear within a population, may vary. All populations have a tendency, over time, to approach homozygosity (AA or aa). This "genetic drift" is a direct result of both natural and artificial selection. Genetic drift occurs as we select specific values for phenotypic expression thus altering genotype. Fixed characteristics, or those qualities that distinguish one pure breed from the other, are a consequence of genetic drift through artificial selection. Ex.: Coat color, size and temperament. . The high frequency of cryptorchidism within certain breeds as opposed to others, is a direct reflection of selection. A bilateral cryptorchid is infertile and thus, is unable to produce offspring. As a result, the undesirable allele is self limiting through natural and artificial selection as they are unable to bear young with the same defect. However, the unilateral cryptorchid is fertile. Through artificial selection, we may also decrease the percentage of undesirable characters by eliminating affected animals (those with one testicle but fertile) from breeding programs, thus preventing them from producing 'carrier' and similarly affected progeny. . If breeders continually introduce "mutants" into a population, that population will have a natural tendency to move toward homozygosity for the recessive allele/s; in this case, cryptorchidism. Over many generations, cryptorchidism becomes the norm rather than the exception. In other words, we "fix" the allele for cryptorchidism. Conversely, a population will experience a decrease in cryptorchidism if we systematically eliminate affected animals from the breeding program. Where cryptorchidism may have been the norm, it now becomes the exception. Thus, results are not seen overnight but rather, are realized over a period of generations. . We cannot hope to eliminate the existence of undesirable alleles. We can, however, minimize the frequency with which they occur. Understanding that every breeder has a right to assign importance where they feel it is most deserved, each and every problem is as worthy as the next. Whether considering cryptorchidism, epilepsy, hip dysplasia heart disease, or thyroid disease, the goal should not be to eliminate a single defect but rather, to confront them all with equal fervor so to decrease their incidence within the population. . LEGACY: Responsible breeding practices dictate the future viability of all breeds, and just as we enjoy the legacy of past endeavors, breeders of purebred dogs are obliged to afford the same courtesy to future generations of fanciers. After all, compromising the reproductive capabilities of any population of animals will ultimately lead to its demise while leaving those who contributed, their rightful legacy. . References: . 1.) Small Animal Medical Dictionary, Lorenz and Cornelius Canine and Feline Endocrinology and Reproduction. Feldman and Nelson Tumors Of The Genital System And Mammary Glands 2.) Andrew S. Loar Merks Veterinary Manual,(6th edition), Management of Reproduction: 3.) Sm. Animals Genetic Analysis (5th edition) 4.) Griffiths,Miller,Suzuki, Lewontin and Gelbart: Canine Cryptorchidism 5.) Veterinary Clinics Of North America: Small Aimal Practice-Vol. 21, No. 3, May 1991. 6.) Textbook Of Small Animal Sex/Slatter, Male Reproductive System/Shirley D. Johnston . So the final question is, when breeding, should you select away from this trait? A bilateral cryptorchid is infertile, so is unable to produce offspring. As a result, the undesirable allele is self limiting through natural and artificial selection. But the unliateral cryptorchid is fertile and therefore able to reproduce. . There have been few studies of this trait, while there are many theories about the mode of in heritance of this trait, they all agree that there is a genetic component. . · Bona, S. (1995). A population genetic study of the breeding situation and inherited diseases particularly eye and joint in the Golden Retriever and Labrador (Eine populationsgenetische Untersuchung zur Zuchtsituation und zu erblich determinierten Erkrankungen - insbesondere Augen- und Gelenkserkrankungen- beim Golden und Labrador Retriever). Abstract: The first half of this thesis describes the origins of the 2 breeds,the breeding of retrievers in Germany, standards and regulations forthe breeds, and inherited defects and diseases in retriever breeds. The second half reports the authors investigations. Litter size averaged 7.86 and 7.42 in the Golden Retriever and Labrador respectively. The trait appeared to be unaffected by inbreeding. Heritabilities in the 2 breeds were 0.128 plus or minus 0.0475 and 0.158 plus or minus 0.0949 respectively for hip dysplasia, 0.292 plus or minus 0.126 and 0.117plus or minus 0.138 for elbow dysplasia, and 0.068 plus or minus 0.07 (Golden Retriever only) for cryptorchidism. The incidence of progressive retinal atrophy in the dogs studied was 3.9%, and that ofheterozygotes for the defect approximately 32%. . · Cox, V. S., Wallace, L. J., & Jessen, C. R. (1978). An anatomic and genetic study of canine cryptorchidism. Teratology, 18, 233-240. Abstract: Cryptorchidism was found in 12 dogs of a colony of over 100 purebred and crossbred Miniature Schnauzers. At least nine affected dogs were derived from the same sire directly or indirectly. Of the 12 cases, five were unilateral and seven were bilateral. Eight affected dogs were studied anatomically. All unilateral retained testes were on the right side, and right sided bilateral retained testes were always smaller than their left sided counterparts. With one exception, ectopic testes were in the abdominal position. Developmentally the morphological appearance of the epididymis of abdominal testes was very primitive in bilateral cases but nearly normal in the unilateral cases. The degree of inbreeding was greater for bilateral cases than unilateral cases. The high incidence of cryptorchidism in this colony indicates the hereditary nature of the condition in the Miniature Schnauzer; morphological observations suggested a multiple gene defect. . · Pendergrass, T. W. & Hayes Jr, H. M. (1975). Cryptorchism and related defects in dogs: epidemiological comparison with man. Teratology, 12, 51-55. Abstract: A study of 1266 dogs with cryptorchidism from a series of large clinics and hospitals showed eight breeds (Chihuahua, Miniature Schnautzer, Pomeranian, miniature Poodle, standard Poodle, Shetland Sheepdog, Siberian Husky, Yorkshire Terrier) had an excess risk of the defect. Mixed breeds, Beagles and Labrador Retrievers had a significantly low risk. Review of the medical histories revealed that hip dysplasia, patellar dislocation, defects of the penis and prepuce, and umbilical hernia were excessively associated with cryptorchidism. Testicular neoplasms were diagnosed 10.9 times more commonly among cryptorchid dogs. . · Romagnoli, S. E. (1991). Canine cryptorchidism. Vet Clin.North Am Small Anim Pract, 21, 533-544. Abstract: Canine cryptorchidism is a congenital defect that results from sex- limited autosomal recessive gene(s). Incidence is higher in some breeds, especially in smaller and inbred ones. Parents of affected puppies are carriers. Unilateral cryptorchid dogs can be fertile, and affected individuals and their siblings should be eliminated from a breeding program to decrease incidence of the defect. Androgen and gonadotropin treatments have been tried with little or no success. Bilateral orchidectomy is the treatment of choice because of the common sequelae of testicular neoplasia and torsion. . · Sittmann, K. (1980). Cryptorchidism in dogs: genetic assessment of published data. In (pp. 247). Abstract: The analyses involved official records compiled for dissertations on German Boxers (GB) by 3 authors (1938, 1939 and 1968) and on German Shepherd Dogs (GS) by 3 authors (1932, 1957 and 1964). Extensive under-reporting is illustrated by incidences of 3.9 plus or minus 0.2% and 6.1 plus or minus 0.3%, the 1st for males registered in the studbook (1964), and the 2nd for a sample, included in the 1st, from the more reliable "family performance file" (1957). Biases were studied via litter size distributions, sex ratios and affected- male full-sib and half-sib families. Heritability estimates were 0.50-0.80. However, segregation ratio estimates for GB sibships with at least 1, 2 and 3 cryptorchids of 16.0 plus or minus 5.1, 29.6 plus or minus 5.1 and 49.5 plus or minus 13.6% resp., and similar estimates for subsamples of GBs, favour very few recessive genes over polygenic inheritance with 1 or 2 thresholds. . V. N. Meyers-Wallen. Inherited disorders in sexual development. J Hered 90 (1):93-95, 1999. There is no abstract, but cryptorchidism is listed under "Miscellaneous Male pseudohermaphroditism: "Cryptorchidism is included here because the mechanism of abnormal testis descent is incompletely understood. While cryptorchidism can be associated with other defects in sexual development, it also occurs as an isolated defect. As an isolated defect, cryptorchidism is the most common disorder of sexual development in dogs, occurring in as many as 13% of dogs presented to small animal clinics (Dunn et al, 1968). it is likely that some forms of canine cryptorchidism are inherited, since there is a high frequency in some breeds and within some families of breeds, and the frequency increases with inbreeding. In Angora goats, it has been proposed that cryptorchidism is inherited as a single locus, sex-limited, autosomal recessive trait. In swine, it has been reported as a sex-limited autosomal trait involving at least two gene loci." |
