X trisomy in an infertile bitch: cytogenetic, anatomic, and histologic studies

Chromosome abnormalities in dogs with disorders of sex development (DSD)

Disorders of sex development (DSD) caused by chromosome abnormalities are rarely diagnosed in dogs. In this report, there is a focus on five DSD cases in which the dogs had abnormal karyotypes. All animals were recognized by owners as females, however, these dogs had a large number of reproductive defects. Among these were abnormal external genitalia such as an enlarged clitoris, abnormal development of the labia, abnormal location of the vulva and urethral orifice, and other abnormalities were observed in four dogs. Gonadal histology assessments were conducted on three dogs and there were diagnoses of the presence of an ovary, inactive testes, and ovotestis with calcification in ovarian follicles. Results from cytogenetic analysis indicated there were the following karyotypes: (a) X trisomy in a mosaic form (79,XXX/78,XX); (b) Robertsonian translocation in a mosaic form (77,XX,rob/78,XX); (c) nonmosaic X/autosome translocation (78,X,t(X;A)); (d) X/autosome translocation in a mosaic form (78,X,t(X;A)/78,XX); and (e) leukocyte chimerism (78,XX/78,XY). The findings in the present study, emphasize that cytogenetic analysis is essential for elucidating the pathogenesis of DSD in dogs.

Clinical Cytogenetics of the Dog: A Review

The dog is an important companion animal and has been recognized as a model in biomedical research. Its karyotype is characterized by a high chromosome number (2n = 78) and by the presence of one-arm autosomes, which are mostly small in size. This makes the dog a difficult subject for cytogenetic studies. However, there are some chromosome abnormalities that can be easily identified, such as sex chromosome aneuploidies, XX/XY leukocyte chimerism, and centric fusions (Robertsonian translocations). Fluorescence in situ hybridization (FISH) with the use of whole-chromosome painting or locus-specific probes has improved our ability to identify and characterize chromosomal abnormalities, including reciprocal translocations. The evaluation of sex chromosome complement is an important diagnostic step in dogs with disorders of sex development (DSD). In such cases, FISH can detect the copy number variants (CNVs) associated with the DSD phenotype. Since cancers are frequently diagnosed in dogs, cytogenetic evaluation of tumors has also been undertaken and specific chromosome mutations for some cancers have been reported. However, the study of meiotic, gamete, and embryo chromosomes is not very advanced. Knowledge of canine genome organization and new molecular tools, such as aCGH (array comparative genome hybridization), SNP (single nucleotide polymorphism) microarray, and ddPCR (droplet digital PCR) allow the identification of chromosomal rearrangements. It is anticipated that the comprehensive use of chromosome banding, FISH, and molecular techniques will substantially improve the diagnosis of chromosome abnormalities in dogs.

Gonadal and sex differentiation abnormalities of dogs and cats

The molecular steps in normal sexual development were largely discovered by studying patients and animal models with disorders of sexual development (DSD). Although several types of DSD have been reported in the cat and dog, which are often strikingly similar to human DSD, these have been infrequently utilized to contribute to our knowledge of mammalian sexual development. Canine and feline cases of DSD with sufficient evidence to be considered as potential models are summarized in this report. The consensus DSD terminology, and reference to previous terminology, is used to foster adoption of a common nomenclature that will facilitate communication and collaboration between veterinarians, physicians, and researchers. To efficiently utilize these unique resources as molecular tools continue to improve, it will be helpful to deposit samples from valuable cases into repositories where they are available to contribute to our understanding of sexual development, and thus improve human and animal health.

The pseudoautosomal region and sex chromosome aneuploidies in domestic species

The pseudoautosomal region (PAR) is a unique and specialized segment on the mammalian sex chromosomes with known functions in male meiosis and fertility. Detailed molecular studies of the region in human and mouse show dramatic differences between the 2 PARs. Recent mapping efforts in horse, dog/cat, cattle/ruminants, pig and alpaca indicate that the PAR also varies in size and gene content between other species. Given that PAR genes escape X inactivation, these differences might critically affect the genetic consequences, such as embryonic survival and postnatal phenotypes of sex chromosome aneuploidies. The aim of this review is to combine the available information about the organization of the PAR in domestic species with the cytogenetic data on sex chromosome aneuploidies. We show that viable XO individuals are relatively frequently found in species with small PARs, such as horses, humans and mice but are rare or absent in species in which the PAR is substantially larger, like in cattle/ruminants, dogs, pigs, and alpacas. No similar correlation can be detected between the PAR size and the X chromosome trisomy in different species. Recent evidence about the likely involvement of PAR genes in placenta formation, early embryonic development and genomic imprinting are presented.

Trisomy-X with estrous cycle anomalies in two female dogs

Two female dogs were presented with a history of abnormal estrous cycles and infertility, despite multiple breedings. Medical therapy to correct the cycle anomalies did not result in pregnancy. Cytogenetic analysis of blood lymphocyte cultures in each dog revealed three copies of the X chromosome in each cell, constituting a 79,XXX karyotype (trisomy-X). Both dogs were eventually ovariohysterectomised and histological evaluation revealed hypoplastic ovaries and an absence of normal follicular structures. However, partial or immature follicles were noted, which may have been sufficient to cause both females to initiate cycling. The history and clinical characteristics found in these dogs were compared to those described in three other dogs reported with trisomy-X, as well as those reported in other species. These findings highlighted the importance of cytogenetic studies in fertility evaluation and achieving a definitive diagnosis for infertility in the bitch.