Ring Y chromosome as an unusual cause of severe oligozoospermia.

Summary: We report a 27-year-old male with a rare chromosomal anomaly involving a ring Y chromosome (RCY). Our patient presented with severe oligozoospermia in the absence of other overt phenotypic abnormalities and was ultimately found to have mosaicism involving a ring Y chromosome. This case highlights the importance of considering structural Y chromosome abnormalities in the evaluation of male infertility, even in individuals with otherwise normal pubertal development and secondary sexual characteristics. Learning points: RCY is a rare but important genetic cause of male infertility and should be considered in the evaluation of severe oligozoospermia or azoospermia. The clinical phenotype of RCY ranges from a normal male phenotype with infertility to phenotypic females with features of Turner syndrome. This is influenced by the presence or absence of Y-linked genes and the degree of 45,X mosaicism. The presence of a 45,X cell line in individuals with RCY mosaicism has been associated with gonadal anomalies, particularly dysgenesis and cryptorchidism.