Familial marker chromosome due to 3:1 disjunction of t(9;15) in a grandparent

Small supernumerary marker chromosomes derived from chromosomes 6 and 20 in a woman with recurrent spontaneous abortions

In this report, we describe a case of multiple small supernumerary marker chromosomes (sSMC) presenting with recurrent abortions. Peripheral blood lymphocytes of a young, healthy and non-consanguineous couple who asked for genetic evaluation after two spontaneous miscarriages were obtained for karyotypes. Lymphocytes of the woman were analyzed by FISH techniques and DNA was extracted and used for array CGH investigation. Karyotyping revealed 48,XX,+2mar[24]/47,XX,+mar[5]/46,XX[3] for the woman and 46,XY for her husband. FISH analysis showed that the two sSMC consisted of chromosomes 6 and 20. Array CGH analysis showed gains of the 6p11.2q12 (9 Mb) and 20 p11.21 (3.3 Mb) chromosomal regions with a total of 42 genes present on both sSMC. Our findings support also the hypothesis that the modification of the expression of some genes involved in embryo implantation, like THBD gene, could be responsible in the recurrent abortions. This report underpins the necessity of array CGH for characterizing precisely sSMC and helping in genotype-phenotype correlations. Furthermore, a literature review on sSMC is included.

Duplication of 8p23.1: a cytogenetic anomaly with no established clinical significance

We present seven families with a cytogenetic duplication of the short arm of chromosome 8 at band 8p23.1. The duplication has been transmitted from parents to offspring in four of the seven families. In three families, the source of the extra material and its euchromatic origin were established using FISH with a YAC which was mapped to 8p23.1 and a whole chromosome paint for chromosome 8. FISH signals from this YAC were significantly larger on the duplicated chromosome compared with the normal chromosome in all six family members tested. Comparative genomic hybridisation (CGH) on a representative subject was consistent with these results. The families were ascertained for a variety of mostly incidental reasons including prenatal diagnosis for advanced maternal age. The transmission of this duplication by multiple phenotypically normal family members with no history of reproductive loss suggests the existence of a novel class of 8p23.1 duplications, which can be regarded as euchromatic variants or duplications with no phenotypic effect.

Extra small marker chromosome associated with normal phenotype due to 3:1 disjunction of t(14;22) in a parent. Implications for the origin of marker chromosomes

A family with segregation of a translocation t(14;22) (q31;q11) is is reported. The proband was ascertained by chromosome analysis after repeated spontaneous abortions in his wife. His normal sister was found to have the karyotype 47,XX,+ der (22). The small size and banding pattern of chromosome 22 make it difficult to determine the breakpoint with certainty, but it was judged to be at q11. This small marker chromosome could thus be similar to the one found in the cat eye syndrome, and further studies may cast light on gene(s) involved in this syndrome.