We report a case of familial small supernumerary marker chromosome 15 in a phenotypically normal female with 4 recurrent spontaneous abortions and a healthy child. The initial karyotype showed a small, bisatellited, apparently metacentric marker chromosome, 47,XX,+idic(15)(q11.1), maternally inherited. The proband's mother was mosaic for the idic(15)(q11.1) without pregnancy loss. Reexamination of the proband's karyotype revealed cryptic mosaicism for 1 ring and 1 minute chromosome derived de novo from chromosome 9 in 2% of the metaphases. In FISH analysis, the patient's karyotype was mos 47,XX,+idic(15)(q11.1)mat[100]/49,XX,+idic(15)(q11.1)mat,+r(9;9;9;9),+der(9)dn[2]. The second spontaneous abortion had trisomy 9 (47,XX,+9); the third had mosaic trisomy 9 in 21% of the nuclei and isodicentric chromosome 15 in 36% of the nuclei (mos 48,XN,+9,+idic(15)(q11.1)/47,XN,+9/47,XN,+idic(15)(q11.1)/46,XN). The first and fourth abortions were not cytogenetically studied. The cause of the spontaneous abortions in this patient is likely the cryptic mosaicism for ring and minute chromosomes 9, and gonadal mosaicism is most probable, due to the 2 abortions.
Case report of a pseudo‐isodicentric chromosome 9 resulting in mosaic trisomy 9