Natural Transmission of b2/b3 Subdeletion or Duplication to Expanded Y Chromosome Microdeletions

BACKGROUND: Y chromosome microdeletions are usually de novo mutations, but in several cases, transmission from fertile fathers to infertile sons has been reported. MATERIAL/METHODS: We report 3 cases of infertile patients who inherited expanded Y chromosome microdeletions from their fathers, who carried b2/b3 subdeletion or duplication. The karyotype was analyzed using G-banding. High-throughput sequencing was used to detect AZF region microdeletions. RESULTS: Cytogenetic analysis showed a normal karyotype 46,XY in patient 1 (P1), patient 2 (P2), and their fathers (F1 and F2). Patient 3 (P3) and his father (F3) presented a karyotype of 46,XY,Yqh-. High-throughput sequencing for the AZF disclosed an identical b2/b3 subdeletion in the F1 and F2. P1 had an AZFc deletion that accounted for 3.5 Mb, and P2 had an AZFa+b+c microdeletion that accounted for 10.5 Mb. F3 had a b2/b3 duplication of 1.8Mb, but P3 had an AZFb+c deletion of 6.2 Mb. CONCLUSIONS: Our findings suggest that b2/b3 partial deletion or duplication can lead to structural instability in the Y chromosome and be a risk factor of complete deletion of AZFc or more expanded deletion during transmission.