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Knowledge of the molecular background of disorders of sex development (DSD) in dogs with normal sets of XY chromosomes (XY DSD) is very scarce. However, extensive studies have been carried out in humans, showing that polymorphisms and mutations of numerous genes, including SRY, MAMLD1, SRD5A2, and AR, are associated with or responsible for XY DSD. In this study, we analyzed the entire coding sequence of these genes in 7 dogs (78,XY) with ambiguous external genitalia (hypospadias, cryptorchidism, bifid scrotum, or rudimentary penis). The most common disorder was hypospadias (6 cases), followed by cryptorchidism (4 cases). The co-occurrence of both abnormalities was observed in 3 dogs. Polymorphisms were found in MAMLD1 (3 SNPs), SRD5A2 (5 SNPs), and AR (2 STRs and 1 SNP), while SRY was monomorphic. However, the distribution of the polymorphic variants in the DSD dogs and 11 control XY dogs did not differ significantly. Our study suggests that an association between the polymorphisms of the studied candidate genes and hypospadias or cryptorchidism is unlikely in dogs. We thus support the recent suggestion that hypospadias is not rare in this species, and moreover, we show that co-occurrence of hypospadias and cryptorchidism can be quite frequent.

Hypospadias, the abnormal position of the urethral orifice, is considered a rare congenital malformation of the reproductive organs in male dogs. We present 5 new cases of hypospadias - 2 of the penile type in German Shepherd Dogs and 3 perineal types in a Bavarian Mountain Hound, a French Bulldog, and an American Staffordshire Terrier. Other abnormalities (rudimentary or underdeveloped penis, incompletely formed preputial sheath, and bilateral cryptorchidism) were also observed. Molecular analysis of all cases revealed the presence of Y-linked genes (SRY and ZFY). Cytogenetic and histological analysis could be performed for only 2 cases: a normal male sex chromosome complement (78,XY) and spermatogenetically inactive testicles were observed. A retrospective search for hypospadias in 19,950 medical records of male dogs from a single veterinary clinic in Poland (2006-2017) was also performed. Altogether, 10 reports of penile hypospadias were found (0.05%). The majority of the reports concerned German Shepherd Dogs (8 cases among 1,511 male dogs of this breed), and thus, the estimated incidence of hypospadias in this breed was 0.5%. Moreover, we performed a review of 26 cases of canine hypospadias reported in the years 2004-2017. Our study and the review of the literature suggest that hypospadias is not rare in dogs and that some breeds (such as German Shepherd Dog and Boston Terrier) may be prone to this disorder.