Carriers of structural chromosomal anomalies, translocations and inversions are at increased risk of aneuploid gametes production. Besides the direct effect on the involved chromosomes, these rearrangements might disturb the segregation of other structurally normal chromosomes during meiosis. Such event is known as interchromosomal effect. In this study, six male carriers of translocations, four reciprocals and two Robertsonians, were investigated. In addition, seven fertile men with normal 46,XY karyotypes and normal sperm characteristics were enrolled as a control group. Spermatic fluorescent in situ hybridisation specific for chromosomes X, Y, 18, 21 and 22 was carried out. The Mann-Whitney U-test was used to compare the aneuploidy rates between patients and controls. All translocation carriers showed significantly increased frequencies of disomy of all investigated chromosomes, and diploid gametes compared with the control group (p < .05). However, disomy XY was not significantly different between controls and patients (p > .05). We have also observed a considerable interindividual variability in disomy and diploidy rates. These results confirm that the interchromosomal effect seems to exist and could contribute to higher rates of abnormal prenatal aneuploidy, resulting in a small increase in the risk of miscarriage and birth of children with congenital abnormalities and a potential reduction in fertility.

BackgroundSmall Supernumerary Marker Chromosomes (sSMC) are rare chromosomal abnormalities, which have abnormal banding arrangement and take many shapes. Several disorders have been correlated with sSMC presence. The aim of this study is to characterize the sSMC derived from chromosome 18 by Fluorescence in situ hybridization (FISH) and Array Comparative Genomic Hybridization (aCGH).ResultsNine children with dysmorphic features have been investigated. They have these features in common: a triangular face, low-set ears, a large mouth with a thin upper lip, and a horizontal palpebral fissure. Epicanthus and strabismus were present in two patients. In addition, we have noticed microcephaly and mental and/or developmental delay with low birth weight. However, two patients had standard birth weight; one patient had hypospadias; two had skin problems; and three showed different congenital heart defects. One patient had corpus callosum hypoplasia. Systematic karyotype analysis revealed a de novo supernumerary chromosome. Array CGH showed a gain in copy number on the short arm of chromosome 18 in the nine cases. In one case, the sSMC seemed to be in mosaic. The breakpoints of the marker were identified using aCGH and FISH. Thus, the sSMC led to 18p tetrasomy with approximately 14 Mb lengths, between 364344 and 14763575 based on the human genome version 18.ConclusionsThese results have been completed by FISH in order to ascertain the shape of the sSMC. Our results confirm the uniqueness and particularity of the iso18p syndrome on the phenotypic as well as on the genetic level.

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