Monorchidism in a Phenotypic Mare With a 64,XY, SRY-Positive Karyotype

Disorders of sexual development (DSD) are associated with atypical chromosomal, gonadal, or phenotypic sex. It is likely that the number of cases of DSD are underestimated in the equine population. Monorchidism in the horse is very rare. This case report describes the clinical assessment of a phenotypic mare with stallion-like behavior which led to the diagnosis of a DSD. A 4-year-old Quarter Horse mare presented in good body condition, with normal external genitalia for a mare, and normal mammary glands with two bilaterally symmetric teats. No uterus, cervix, or gonads were detected on transrectal palpation. Transrectal ultrasonography revealed a single gonad in the right dorsal abdomen with the morphologic appearance of a testicle. Presurgical hormonal evaluation revealed elevated serum testosterone and anti-Müllerian hormone (AMH) concentrations. The right gonad was successfully removed via standing exploratory laparoscopy and submitted for histopathology. No gonad was identified on the left side during laparoscopy. Histopathologic examination confirmed that the excised gonad was a testicle. Cytogenetic and molecular analysis revealed a 64,XY, SRY-positive chromosomal constitution. Hormonal evaluation 5 weeks after surgery revealed low serum testosterone and AMH levels. A diagnosis of monorchidism was based on ultrasound examination, laparoscopic exploration of the abdomen, removal of a single gonad, and a subsequent decrease in serum testosterone and AMH concentrations to basal levels. In summary, a combination of clinical signs, endocrine evaluation, chromosomal and molecular analysis, and histopathology can be used in the diagnosis of DSD conditions.

Horse Clinical Cytogenetics: Recurrent Themes and Novel Findings

Clinical cytogenetic studies in horses have been ongoing for over half a century and clearly demonstrate that chromosomal disorders are among the most common non-infectious causes of decreased fertility, infertility, and congenital defects. Large-scale cytogenetic surveys show that almost 30% of horses with reproductive or developmental problems have chromosome aberrations, whereas abnormal karyotypes are found in only 2-5% of the general population. Among the many chromosome abnormalities reported in the horse, most are unique or rare. However, all surveys agree that there are two recurrent conditions: X-monosomy and SRY-negative XY male-to-female sex reversal, making up approximately 35% and 11% of all chromosome abnormalities, respectively. The two are signature conditions for the horse and rare or absent in other domestic species. The progress in equine genomics and the development of molecular tools, have qualitatively improved clinical cytogenetics today, allowing for refined characterization of aberrations and understanding the underlying molecular mechanisms. While cutting-edge genomics tools promise further improvements in chromosome analysis, they will not entirely replace traditional cytogenetics, which still is the most straightforward, cost-effective, and fastest approach for the initial evaluation of potential breeding animals and horses with reproductive or developmental disorders.

Impaired Reproductive Function in Equines: From Genetics to Genomics

Fertility is one of the key factors in the economic and productive success of the equine industry. Despite this, studies on the genetic causes affecting reproductive performance are scarce, especially in mares, where the genetic architecture of the reproductive traits is extremely complex. Today, with the increasing availability of new genomic methodologies for this species, we are presented with an interesting opportunity to understand the genetic basis of equine reproductive disorders. These include, among others, novel techniques for detecting chromosomal abnormalities, whose association with infertility in horses was established over 50 years ago; new sequencing technologies permitting an accurate detection of point mutations influencing fertility, as well as the study of inbreeding and molecular homozygosity, which has been widely suggested as one of the main causes of low reproductive performance in horses. Finally, over the last few years, reproductive performance has also been associated with copy number variants and candidate genes detected by genome-wide association studies on fertility traits. However, such studies are still scarce, probably because they depend on the existence of large and accurate phenotypic datasets of reproductive and/or fertility traits, which are still difficult to obtain in equines.

Teratoma Associated With Testicular Tissue in a Female-Like Horse With 64,XY (SRY-Positive) Disorder of Sex Development

A four-year-old female-like Quarter Horse was admitted for clinical evaluation because of masculinized-aggressive behavior and lack of estrous signs. On external inspection, a hypertrophied clitoris and prominent muscles were observed. On gynecological examination, apparently normal mammary glands, vulva, vagina, and cervix were noted. On the other hand, the uterus had no tone and was smaller than normal. The left gonad was very soft on palpation and the right gonad was mostly firm, irregular, and wider than the left gonad. On ultrasound examination, there were no signs of regular ovarian structure or follicular activity. Because of the different shapes and consistencies of the gonads and a suspicion of increased testosterone production, a bilateral gonadectomy was recommended. Blood was collected for testosterone levels quantification and for cytogenetic and molecular investigations. After removal, gonads were analyzed macroscopically and sections were sent for histopathological examination. A final diagnosis of benign adult teratoma associated with seminiferous tubules and Leydig cells was made. On cytogenetic and molecular analyses, a normal diploid number of 64 chromosomes and the presence of the XY sex chromosomes were seen in all cells, as well as the SRY gene. Testosterone levels were higher than normal before surgery and were reduced after gonads removal. In conclusion, the masculinized behavior was probably caused by increased testosterone levels produced by testicular tissue, in a female-like horse with 64,XY SRY-positive disorder of sex development, which was associated with a teratoma.

Genetics of Equine Reproductive Diseases

Reproductive disorders are genetically heterogeneous and complex; available genetic tests are limited to chromosome analysis and 1 susceptibility gene. Cytogenetic analysis should be the first test to confirm or rule out chromosomal aberrations. No causative genes/mutations are known. The only available genetic test for stallion subfertility is based on a susceptibility gene FKBP6. The ongoing progress in equine genomics will improve the status of genetic testing. However, because subfertile phenotypes do not facilitate collection of large numbers of samples or pedigrees, and clinical causes of many cases remain unknown, further progress requires constructive cross-talk between geneticists, clinicians, breeders, and owners.

Characterization of A Homozygous Deletion of Steroid Hormone Biosynthesis Genes in Horse Chromosome 29 as A Risk Factor for Disorders of Sex Development and Reproduction

Disorders of sex development (DSD) and reproduction are not uncommon among horses, though knowledge about their molecular causes is sparse. Here we characterized a ~200 kb homozygous deletion in chromosome 29 at 29.7-29.9 Mb. The region contains AKR1C genes which function as ketosteroid reductases in steroid hormone biosynthesis, including androgens and estrogens. Mutations in AKR1C genes are associated with human DSDs. Deletion boundaries, sequence properties and gene content were studied by PCR and whole genome sequencing of select deletion homozygotes and control animals. Deletion analysis by PCR in 940 horses, including 622 with DSDs and reproductive problems and 318 phenotypically normal controls, detected 67 deletion homozygotes of which 79% were developmentally or reproductively abnormal. Altogether, 8-9% of all abnormal horses were homozygous for the deletion, with the highest incidence (9.4%) among cryptorchids. The deletion was found in ~4% of our phenotypically normal cohort, ~1% of global warmblood horses and ponies, and ~7% of draught breeds of general horse population as retrieved from published data. Based on the abnormal phenotype of the carriers, the functionally relevant gene content, and the low incidence in general population, we consider the deletion in chromosome 29 as a risk factor for equine DSDs and reproductive disorders.

Androgen Receptor Gene Variants in New Cases of Equine Androgen Insensitivity Syndrome

In the domestic horse; failure of normal masculinization and virilization due to deficiency of androgenic action leads to a specific disorder of sexual development known as equine androgen insensitivity syndrome (AIS). Affected individuals appear to demonstrate an incoherency between their genetic sex and sexual phenotype; i.e., XY-sex chromosome constitution and female phenotypic appearance. AIS is well documented in humans. Here we report the finding of two novel genetic variants for the AR-gene identified in a Tennessee Walking Horse and a Thoroughbred horse mare; each in individual clinical cases of horse AIS syndrome.

Analysis of testosterone pathway genes in dogs (78,XY; SRY-positive) with ambiguous external genitalia revealed a homozygous animal for 2-bp deletion causing premature stop codon in HSD17B3

The genetic background of disorders of sex development (DSD) in dogs with a normal male sex chromosome set (78,XY) is poorly described. In this study, we present for the first time, an analysis of six genes of the testosterone pathway, encoding enzymes (CYP17A1, HSD3B2, HSD17B3, SRD5A2) and transcription factors (NR5A1, AR). The entire coding sequence and flanking regions of the introns, 5'-UTR and 3'-UTR were analyzed in five DSD dogs (78,XY, SRY-positive) with ambiguous external genitalia and in 15 control dogs. A homozygous deletion of 2 bp in exon 2 of HSD17B3 (hydroxysteroid 17-beta dehydrogenase 3) was found in a Dachshund dog with enlarged clitoris, vulva and abdominal gonads and decreased serum testosterone level. In silico analysis revealed that this deleterious variant causes truncation of the encoded polypeptide (from 306 to 65 amino acids) and deprivation of the active site of the encoded enzyme. Genotyping of 23 control Dachshund dogs showed a normal homozygous genotype. Thus, we assumed that the 2-bp deletion is the causative variant. Moreover, 24 SNPs (four in CYP17A1, three in HSD3B2, six in HSD17B3, five in SRD5A2, one in AR and five in NR5A1), two intronic indels (one in HSD3B2 and one in SRD5A2) and two microsatellite polymorphisms in exon 1 of AR were found. Six SNPs appeared to be novel. No association with DSD phenotype was observed. Identification of the first case of DSD in domestic animals caused by a deleterious variant of a gene involved in testosterone synthesis showed that these genes are important candidates in such studies.

Disorders of sex development in cats with different complements of sex chromosomes

The genetic background of disorders of sex development (DSDs) in cats is poorly understood, due to a relatively low number of such studies in this species. Here we present three new DSD cases with different complements of sex chromosomes. The first, an Oriental Shorthair cat with a rudimentary penis, abdominal atrophic testicles and lack of uterus appeared to be a freemartin, since leucocyte chimerism XX/XY and a lack of Y-linked genes (SRY and ZFY) were observed in DNA isolated from hair follicles. XXY trisomy was identified in the second case, a tortoiseshell Devon Rex male cat with atrophic scrotal testicles and a normal penis. Finally, a European Shorthair cat with atrophic testicles in a bifid scrotum, rudimentary penis and a lack of uterus had XY complement, including Y chromosome of normal size and morphology. Also presence of eight Y-linked genes, detected by PCR, was confirmed. Due to the low testosterone level in this last patient, we searched for a causative mutation in two candidate genes (HSD3B2 and HSD17B3) involved in the metabolism of this steroid hormone. Altogether, five polymorphic sites in HSD3B2 and two in HSD17B3 were found, but none of them showed associations with DSD phenotype. We thus excluded a possibility that the causative mutation is present in these genes. In conclusion, we confirmed that analysis of the sex chromosome complement is a crucial step in diagnosis of DSDs. However, extensive molecular studies of the genes involved in sex development are needed to elucidate the causes of DSDs in cats with normal complements of sex chromosomes.

Genotype-phenotype correlation and identification of two novel SRD5A2 mutations in 33 Chinese patients with hypospadias

Hypospadias, a common congenital malformation of male external genitalia, is characterized mainly by an aberrant opening of the urethra on the ventral side of the penis. Depending on the severity of the disease, it can be classified into three types: anterior, middle, and posterior. In our study, 33 patients with hypospadias were recruited, including eight with anterior hypospadias and 25 with posterior hypospadias. We performed mutation analysis of the SRD5A2, AR and HSD17B3 genes in these patients. Eight different SRD5A2 mutations were detected in 15 patients with posterior hypospadias (60%, 15/25), including six previously described mutations (p.Q6X, Q71X, p.L20P, p.G203S, p.R227Q, and p.R246Q) and two novel mutations (p.G196R and p.L73Pfs^∗17). One AR gene mutation (p.A597T) was found in a patient and no HSD17B3 mutations were detected. Additionally, we carried out routine semen analyses in all adult patients. Combing mutation analysis with semen examination results, showed that whole five adult patients who carried SRD5A2 mutations had abnormal semen quality. In summary, all the detected mutations were responsible for the clinical features observed in these 16 patients. Our data suggest that mutations of the SRD5A2 gene are the main causes of posterior hypospadias and seem to affect the semen quality of adult patients, whereas mutations in AR and HSD17B3 gene were rare in these hypospadias patients. Our study expanded the SRD5A2 mutation spectrum in the Han Chinese population and provided useful information for genetic and reproductive counselling for patients with hypospadias.