- Case Report
- Open Access
The first case of 38,XX (SRY-positive) disorder of sex development in a cat
© Szczerbal et al.; licensee BioMed Central. 2015
- Received: 24 February 2015
- Accepted: 18 March 2015
- Published: 26 March 2015
SRY-positive XX testicular disorder of sex development (DSD) caused by X;Y translocations was not yet reported in domestic animals. In humans it is rarely diagnosed and a majority of clinical features resemble those which are typical for Klinefelter syndrome (KS). Here we describe the first case of SRY-positive XX DSD in a tortoiseshell cat with a rudimentary penis and a lack of scrotum.
Molecular analysis showed the presence of two Y-linked genes (SRY and ZFY) and a normal sequence of the SRY gene. Application of classical cytogenetic techniques revealed two X chromosomes (38,XX), but further FISH studies with the use of the whole X chromosome painting probe and BAC probes specific to the Yp chromosome facilitated identification of Xp;Yp translocation. The SRY gene was localised at a distal position of Xp. The karyotype of the studied case was described as: 38,XX.ish der(X)t(X;Y)(p22;p12)(SRY+). Moreover, the X inactivation status assessed by a sequential R-banding and FISH with the SRY-specific probe showed a random inactivation of the derivative XSRY chromosome.
Our study showed that among DSD tortoiseshell cats, apart from XXY trisomy and XX/XY chimerism, also SRY-positive XX cases may occur. It is hypothesized that the extremely rare occurrence of this abnormality in domestic animals, when compared with humans, may be associated with a different organisation of the Yp arm in these species.
- Disorder of sex development
- Translocation X-Y
- X chromosome inactivation
Sex chromosome abnormalities are well-known causes of disorders of sex development (DSD) in mammals . In cats XXY trisomy is the most frequently reported abnormality . Identification of this trisomy in cats is easy due to the tortoiseshell coat colour, which is unusual in male cats. Since the gene encoding the orange coat colour is located on the X chromosome, a tortoiseshell pattern, caused by a random X-inactivation, is typical of heterozygous female cats. Also in the human XXY trisomy (Klinefelter syndrome - KS) is the most common sex chromosome aneuploidy, with a prevalence of about 1 in 660 new born boys . The most characteristic clinical features associated with KS include a tall stature, small azoospermic testes and gynecomastia . Cats with XXY trisomy are also infertile, but clinical signs of this disorder vary .
The XX (SRY-positive) male syndrome, officially classified as 46,XX testicular DSD and also known as de la Chapelle syndrome, is rarely diagnosed in humans – 1 in 20 000 newborn boys . This syndrome is caused by a translocation of a fragment of the Y chromosome, carrying the SRY gene, to the X chromosome during paternal meiosis . Interestingly, the phenotype of this syndrome mimics KS to some extent, but major differences concern a lower body height and the presence of maldescended testes . So far, to our best knowledge there have been no reports on SRY-positive XX DSD in domestic animals. In this report we describe the first case of a 38,XX tortoiseshell cat with Xp;Yp translocation and the presence of the SRY gene.
The tortoiseshell coat pattern in male cats suggests a disorder of sex development, related with the presence of two or more X chromosomes. An extensive questionnaire survey comprising data of 4598 male cats revealed that tortoiseshell cats occur rarely - 0.4% . Eleven of these tortoiseshell males were cytogenetically studied and the most common sex chromosome complement was XX/XY chimerism (6 cases), followed by XXY trisomy (2 cases), XY (1 cases) and XX (2 cases) . Identification of the XY complement may indicate that another cell line (XXY or XX) was not detected due to its low incidence. In the case of the XX complement one can hypothesize different scenarios: the presence of a minor cell line (XXY or XY), SRY-negative XX DSD or SRY-positive XX DSD.
Our study showed for the first time that transition of a fragment of the Y chromosome, harbouring the SRY gene, to the X chromosome is responsible for SRY-positive XX DSD in this species. Elucidation of the mechanism responsible for the reported mutation and identification of the break point on feline Yp is not easy, due to its unique organisation, in terms of gene order and size of the pseudoautosomal region (PAR) [9,10]. In the feline Yp the PAR is large (approx. 6.7 Mb) and the distance between the SRY gene and PAR is approx. 1.7 Mb . As a consequence, the SRY gene is located in the proximal half of feline Yp. On the gene map of feline Yp only two multicopy genes (CYorf15 and HSFY) are located more proximally and their copies are present on both sides of the SRY gene . Thus, PCR detection of these genes is not useful in searching for the break point. It has been suggested that a non-allelic homologous recombination (NAHR) is responsible for the X;Y translocation in the human and it was indicated that the NAHR events preferentially happen around the PRKY pseudogene . Unfortunately, there is no information available concerning the orthologous sequence in the cat Y chromosome.
The X inactivation pattern in SRY-positive XX DSD cases, in relation to their phenotype, is still under discussion. Some authors hypothesized that preferential inactivation of XSRY is related with undermasculinization . However, other reports did not confirm this relationship . The studied cat showed a random inactivation pattern and pronounced undermasculinization, and thus our result is in agreement with the latter opinion.
In the recent years an increased number of sex chromosome abnormalities and DSD cases have been reported in cats. Apart from XXY trisomy , also X monosomy was described . Among animals with a normal complement of sex chromosomes the SRY-positive XY DSD form was predominant. These animals had variable phenotypes: urogenital or anogenital congenital abnormalities [15,16], hypospadias , gynecomastia, presence of penis and an empty scrotum , ovotestes and Mullerian and Wolffian duct derivatives . On the other hand, no XX DSD cases were reported . Thus, the presented case (SRY-positive XX DSD) may be considered very rare. The phenotype of this cat (small body size, underdeveloped penis and gonadal dysgenesis) resembled major clinical characteristics of human SRY-positive XX DSD (short stature, cryptorchidism and micropenis).
Two major forms of testicular/ovotesticular XX DSD are recognized in mammals: SRY-positive and SRY-negative. The most common form diagnosed in the human is SRY-positive , while in domestic animal species (dog, pig, goat, horse) the SRY-negative form has only been described . We hypothesize that the probability of SRY translocation on Xp may depend on a different organisation (size of PAR, distance between SRY and PAR, gene order, etc.) of the Yp arm in the human and domestic mammals.
Tissue samples were fixed with 10% formalin. Tissue sections of 3–5 μm in thickness were stained using the Masson–Goldner method (haematoxylin and eosin) and analyzed under an Olympus CX41 light microscope equipped with Olympus digital camera.
DNA was isolated from a blood sample (leukocytes ) collected on EDTA and fibroblasts culture with the use of commercial kits (Blood Mini and Genomic Mini, respectively, A&A Biotechnology, Poland). The Y-linked genes were detected by PCR (SRY) and PCR-RFLP (ZFX/ZFY). PCR conditions, primer sequences and the used restriction enzyme were described earlier by .
The SRY amplicon was purified with Exonuclease I (Thermo Scientific, USA) and Thermosensitive Alkaline Phosphatase (Thermo Scientific, USA) sequenced with the use of a BigDye® Terminator v3.1 Sequencing Kit (Applied Biosystems; USA) and analyzed on an ABI 3130 Genetic Analyzer (Applied Biosystems; USA).
Conventional cytogenetic analysis
Chromosome preparations were obtained from skin fibroblast cultures. Cytogenetic evaluation was carried out with the use of conventional Giemsa staining and R-banding according to the procedures described by Iannuzzi and Di Berardino . Cat chromosomes were identified based on karyotype nomenclature proposed by Cho et al. .
Fluorescence in situ hybridization (FISH)
The locus-specific BAC probes were obtained from the Feline BAC library RPCI-86 (https://bacpac.chori.org/). The following clones - RP86 278G21, RP86-326 L15 and RP86-259I15, specific to the short arm of the Y chromosome were selected, based on [23,24] The whole feline X chromosome painting probe was obtained by flow sorting (kindly provided by Prof. M.A. Ferguson-Smith, Cambridge University, UK). DNA was labelled with biotin-16-dUTP or digoxigenin-11-dUTP by random priming (BAC clone) or DOP-PCR (painting probes) and the standard protocol for FISH experiments was applied, as described earlier by Szczerbal et al. . Microscopic evaluation was carried out under a Nikon E600 Eclipse fluorescent microscope (Melville, NY, USA), equipped with a cooled CCD digital camera and Lucia software.
We thank Prof. M. Ferguson-Smith (Cambridge Resource Centre for Comparative Genomics, Cambridge University, UK) for the flow-sorted feline X chromosome paint. This study was financed by the statutory fund of the Department of Genetics and Animal Breeding (No. 508.534.00.0), Faculty of Veterinary Medicine and Animal Sciences, Poznan University of Life Sciences, Poland.
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