Clinical Cytogenetics of the Dog: A Review

Abstract

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.

Identification of aneuploidy in dogs screened by a SNP microarray

“…During the validation of this array, three cases of aneuploidy were identi ed out of 2,053 samples screened. While monosomy X and trisomy X have been reported many times before in dogs (Szczerbal and Switonski, 2021), this report is the rst time that microarray analysis has been used in dogs to uncover aneuploidy and the rst report of trisomy 38. Figure 1 shows the results of the monosomy and trisomy X dogs as compared to a normal female and a normal male result.…”

“…Cytogenetic anomalies have been identi ed in many different mammalian species including cats (reviewed in Szczerbal and Switonski, 2020) and dogs (reviewed in Szczerbal and Switonski, 2021;). The dog karyotype consists of 38 acrocentric autosome pairs and the X and Y chromosomes (2n = 78).…”

“…The dog karyotype consists of 38 acrocentric autosome pairs and the X and Y chromosomes (2n = 78). Karyotype and FISH analysis has shown sex chromosome anomalies including monosomy X, trisomy X, trisomy XXY, sex chromosomal mosaicism or XX/XY chimeras in dogs primarily presenting with abnormal estrous cycles, infertility, sterility or hypoplastic gonads (Szczerbal and Switonski, 2021), although some dogs with mosaic karyotypes have shown normal estrus. Structural chromosome anomalies have been seen as well, mostly Robertsonian translocations that are apparently balanced.…”

“…Structural chromosome anomalies have been seen as well, mostly Robertsonian translocations that are apparently balanced. Although, some dogs did present with abnormal phenotypes (Szczerbal and Switonski, 2021), it is unclear if these are associated with the cytogenetic anomalies identi ed. Even in the most experienced hands, the dog karyotype is di cult to reconstruct using chromosome banding techniques.…”

“…Thus, the partner chromosomes involved in many of the Robertsonian translocation found have not been identi ed and reciprocal translocations are rarely reported due to the di culties in karyotype analysis (Szczerbal and Switonski, 2021).…”