A Disorder of Sex Development in a Holstein–Friesian Heifer with a Rare Mosaicism (60,XX/90,XXY): A Genetic, Anatomical, and Histological Study

SIMPLE SUMMARY: Disorders of sex development (DSDs) are congenital conditions in which a discordance between chromosomal, gonadal, or phenotypic sex is observed. DSDs are serious problems in animal breeding, as they lead to sterility. In cattle, the most common form of DSD is freemartinism, which manifests as the presence of leukocyte chimerism (XX/XY), and occurs in heifers originating from heterosexual twin pregnancy. Other forms of DSD are rarely observed in this species. In this study, we describe a very rare diploid/triploid (60,XX/90,XXY) condition in a DSD heifer. Comprehensive clinical, anatomical, histopathological and genetic analysis was performed. ABSTRACT: In this study, we describe an eighteen-month-old Holstein–Friesian heifer with a deformed vulva, located abdominally. The heifer showed typical signs of estrus. A comprehensive anatomical and histopathological examination revealed a blind-ended vagina and an additional section of urethra, which became a part of the shortened penis. Cytogenetic analysis showed the presence of two cell lines: 60,XX and 90,XXY. The frequency of the triploid cell line was low (3%) in leukocytes and elevated (35%) in fibroblasts. The molecular detection of Y-linked genes (SRY and AMELY) in the blood, skin, hair follicles, and buccal epithelial cells confirmed the presence of a cell line carrying the Y chromosome. Genotyping of 16 microsatellite markers in DNA isolated from hair follicles and fibroblast culture showed the presence of one (homozygous) or two variants (heterozygous) at all the studied loci, and allowed chimerism to be excluded. We concluded that the heifer had diploid/triploid (60,XX/90,XXY) mosaicism. To our knowledge, this is only the fifth such case to be reported worldwide in this species. Since cytogenetic studies are routinely performed on in vitro cultured leukocytes, we suspect that the prevalence of this chromosome abnormality is underestimated, as it is known from published reports that the frequency of the triploid cell line is usually very low in leukocytes.