Identification of a "cryptic mosaicism" involving at least four different small supernumerary marker chromosomes derived from chromosome 9 in a woman without reproductive success.

OBJECTIVE

To characterize the small supernumerary marker chromosomes (sSMCs) present in the female member of an infertile couple who has no further clinical symptoms.

DESIGN

Case report.

SETTING(S): Faculty of medicine and institute of human genetics and anthropology.

PATIENT(S): A young, healthy, nonconsanguineous couple asked for genetic evaluation for infertility.

INTERVENTION(S): Intracytoplasmic sperm injection, conventional and molecular cytogenetic analyses.

MAIN OUTCOME MEASURE(S): We characterized the sSMCs present in a woman, who was a member of an infertile couple, by molecular cytogenetic techniques.

RESULT(S): The G-banding technique showed that a marker chromosome was present in some of the examined cells describing the 47,XX,+mar[30]/46,XX[70] karyotype. Subsequently, using new fluorescence in situ hybridization (FISH) techniques, four distinguishable sSMCs (cryptic mosaicism), all derived from chromosome 9, were observed, including minute and ring chromosomes. This heterogeneity was impossible to detect by the conventional G-banding technique or conventional FISH technique that were used before the new FISH techniques (subcentromere-specific multicolor-FISH [subcenM-FISH]) and specific probe for the 9q12 band. In each metaphase with sSMCs, only one or two markers were observed. On the basis of the FISH analyses, the patient's karyotype was defined as 47,XX,+min(9)(:p12-->q12:)/47,XX,+min(9)(:p12-->q12::q12-->p12:)/47,XX,+r(9)(::p12-->q12::)/47,XX,+r(9)(::p12-->q12::p12-->q12::)x2/46,XX.

CONCLUSION(S): The presence of sSMCs derived from chromosome 9 could influence the couple's infertility. The new subcenM-FISH techniques are very useful in the characterization of cryptic mosaicisms of marker chromosomes. Additionally, the hypothesis that the 9p12 chromosomal band is an euchromatic variant region without any phenotypic impact other than possible infertility is supported by this case study since the woman shows a normal phenotype.