RESUMEN
Genealogy and cytogenetics examinations were performed on an infertility patient and her family members in the Second Affiliated Hospital of Hainan Medical University on 2016. The unique karyotype of proband: 46, XX, inv(9)(p12q13)dn, inv(20)(p13q13.1), 1qh+mat/46, XX, inv(20)(p13q13.1), 1qh+mat, No.4516, was discovered. The proband suffered from infertility and polycystic ovary syndrome. The proband′s second sister, with a karyotype of 46, XX, inv(20)(p13q13.1)mat, also suffered from polycystic ovary syndrome. The karyotype of the proband′s mother was 46, XX, inv(20)(p13q13.1), 1qh. The karyotype of the proband′s father was 46, XY, ?inv(9)(q32q34), inv(20)(p13p11.2). Inversion of chromosome 20 occurred in two generations of this family. Both the proband and her second old sister inherited the mother′s karyotype rather than the karyotype of their father. The abnormal karyotype may interfere with pregnancy, which leads to infertility. The size of the chromosomes and segments involved in inversion should be considered comprehensively in genetic counselling to provide more accurate genetic counselling information for the carriers, and a solid diagnostic basis for clinicians.