Disorder of sex development in a cat with chromosome mosaicism 37,X/38,X,r(Y)

1 Introduction

Disorders of sex development (DSD), defined as a condition where chromosomal, gonadal or phenotypic sex is atypical, are a well-known problem in domestic animal reproduction (Szczerbal & Switonski, 2016). Three main categories of DSD are distinguished as follows: sex chromosome DSD, XX DSD and XY DSD (Meyers-Wallen, 2012). The most common chromosome mutation causing DSD found in cats is XXY trisomy (Pedersen, Berg, Almstrup, & Thomsen, 2014). However, other abnormalities, such as X monosomy (Szczerbal, Nizanski, et al., 2015), 37,X/38,XY mosaicism (Balogh et al., 2015) or X/Y translocation (Szczerbal, Stachowiak, Dzimira, Sliwa, & Switonski, 2015), have also been reported recently. It is known from human studies that structural rearrangements of the Y chromosome are associated with male infertility or sterility (Dhanoa, Mukhopadhyay, & Arora, 2016).

In this report, we describe a very rare case of DSD in a cat with two cell lines detected in lymphocytes, both carrying sex chromosome abnormalities.

2 Case Report

An 18-month-old European shorthair cat (4.5 kg) with male appearance was subjected to clinical, histological, cytogenetic and molecular studies due to an ambiguous phenotypic sex. The physical examination revealed the presence of undeveloped both penis (Figure 1a) and scrotum. The B-mode ultrasonography in dorsal recumbence was applied. Left testicle was found in the scrotal sac, while the right gonad was abdominally located. A sagittal sonogram of the abdominal cavity visualized a longitudinal structure resembling the uterus. The cat was neutered (Figure 1b) by a veterinary surgeon according to standard Polish veterinary protocols under the consent of the owner and the approval of the local Bioethical Commission for Animal Care and Use in Poznan (Poland).

2.2 Cytogenetic analysis

Chromosome preparations were obtained from a short-term lymphocyte culture according to a standard procedure. Fluorescence in situ hybridization (FISH) with feline X painting probe (kindly provided by Prof. M. A. Ferguson-Smith, Cambridge University, UK), SRY-specific probe (BAC clone RP86-278G21) and telomeric probe (Chrombios GmbH) was performed as described by Szczerbal, Stachowiak, et al. (2015). Hybridization with the SRY-specific probe was also performed on a normal male cat as a reference for the SRY gene location on the Y chromosome. Microscopic evaluation was carried out under Nikon E600 Eclipse fluorescent microscope (Melville, NY, USA) equipped with a cooled CCD digital camera and lucia software (Laboratory Imaging, Praha, Czech Republic).

Conventional cytogenetic analysis including Giemsa staining performed on 100 metaphase spreads revealed the presence of two abnormal cell lines. The first cell line carried X chromosome monosomy (37,X) in 90% (95% confidence interval was 84.1–95.8%) of the analysed cells, and the second had 38 chromosomes, including one X and a small marker chromosome (38,X,+mar) in 10% of the analysed cells (Figure 2a,b). Fluorescence in situ hybridization procedure using the X chromosome-specific probe confirmed the presence of a cell line with X monosomy. The use of the SRY-specific probe revealed that the marker chromosome is derived from the Y chromosome—der(Y) (Figure 2c–e). Therefore, the karyotype of the studied cat was described as 37,X/38,X,+mar.ish der(Y)(SRY+). As the location of the SRY gene was different from a normal, feline Y chromosome (Figure 2f), it is suggested that der(Y) can be a ring chromosome. To verify this hypothesis, a telomeric probe was applied. We observed a single hybridization signal, instead of two expected on both ends of der(Y); thus, we have assumed its ring (r) structure (Figure 2g).

3 Discussion

The DSD are an important breeding issue, as they affect reproduction, and in case of their hereditary forms, a wide spreading of the undesired mutations may occur. Thus, the extensive studies of the genetic background of such disorders have been conducted in domestic animals (Meyers-Wallen, 2012; Parma, Veyrunes, & Pailhoux, 2016; Raudsepp & Chowdhary, 2016; Szczerbal & Switonski, 2016). Nevertheless, structural rearrangements involving sex chromosomes were rarely reported in companion species. Until now, only a single case of DSD cat (phenotypically tortoiseshell female with an underdeveloped penis without spines and no scrotum), caused by X/Y translocation, was reported (Szczerbal, Stachowiak, et al., 2015). In the present study, we have described for the first time a DSD cat carrying two abnormal cell lines—37,X/38,X,r(Y). The application of FISH technique with the telomeric probe indicated a ring morphology of this der(Y). It is known that telomeres play a crucial role in the stabilization of the derivative chromosomes during cell division (Guilherme et al., 2012). Probably, due to mitotic instability of the der(Y), the monosomic cell line was found in the studied case. Such situation was reported in human patients carrying ring Y chromosome, leading to a mosaic karyotype 45,X/46,X,r(Y) and DSD, for example the presence of ambiguous genitalia, gonadal dysgenesis or complete masculinization (Bertini, Canale, Bicocchi, Simi, & Valetto, 2005).

In case of the studied cat, we have observed a high proportion of the X monosomy cell line, despite the presence of testes. A similar case was reported by Balogh et al. (2015), who described a cryptorchid cat with a mosaic karyotype—37,X[96%]/38,XY[4%]. In both cats, a low proportion of cell lines carrying the Y or der(Y) chromosome was observed, but it may not be excluded that in other tissues and organs, including gonads, the proportion of these cell lines was higher and sufficient to drive gonad development into testes.

To the best of our knowledge, it is the first report describing a small marker Y chromosome, having a ring structure, which is associated with DSD and/or infertility in domestic animals. Identification of such cases is also important from the oncological point of view, as the presence of the sequences derived from the Y chromosome in patients with dysgenetic gonads may cause development of gonadal tumours (Oliveira et al., 2009).

Conflict of Interest

None of the authors have any conflict of interest to declare.

Author contributions

Szczerbal, Stachowiak and Nowacka-Woszuk contributed to cytogenetic and molecular analyses. Dzimira and Szczepanska performed clinical examinations and histological studies. Switonski developed the research design and supervised the study. Szczerbal and Switonski were responsible for manuscript preparation and submission.