Mild ring 17 syndrome shares common phenotypic features irrespective of the chromosomal breakpoints location.

Ring 17 syndrome is a rare disorder with clinical features influenced by the presence or deletion of the Miller-Dieker critical region (MDCR). Presence of the MDCR is associated with a mild phenotype, including growth delay (GD), mental retardation (MR), seizures, cafè au lait skin (CALS) spots and minor facial dysmorphisms. Previous studies have been mainly focused on this locus providing poor information about the role of other genes located on the p- and q-arms. Here, we used bacterial artificial chromosome (BAC)/P1 artificial chromosome (PAC) and fosmid clones as fluorescence in situ hybridization (FISH) probes to perform a cyto-molecular analysis of a ring 17 case and found that the breakpoints were close to the telomeric ends. METRNL is the sole gene located on the q-arm terminal end, whereas two open reading frames and the RPH3AL gene are located on the terminal p-arm. To detect possibly unrevealed small deletions involving the transcription units, we used subcloned FISH probes obtained by long-range polymerase chain reaction (PCR), which showed that the investigated regions were preserved. Comparing our findings with other reports, it emerges that different breakpoints, involving (or not) large genomic deletions, present overlapping clinical aspects. In conclusion, our data suggest that a mechanism based on gene expression control besides haploinsufficiency should be considered to explain the common phenotypic features found in the mild ring 17 syndrome.

Masked complex chromosome rearrangement in a child thought to have del(8qter) as the sole cytogenetic abnormality.

Cytogenetic analyses of constitutional diseases have disclosed several chromosomal rearrangements. At the molecular level, these rearrangements often result in the breakage of genes or alteration of genome architecture. Fluorescence in situ hybridization (FISH) and molecular investigations of a patient showing hypotonia and dysmorphic traits revealed a masked complex chromosome abnormality previously detected by G-banding as a simple 8qter deletion. To characterize the genetic rearrangements panels of bacterial artificial chromosomes (BACs) covering 8q24.22-->qter were constructed, and short tandem repeats (STRs) were used to refine the localization of the breakpoints and to assess the parental origin of the defect. Chromosome 8 displayed the breakpoint at 8q24.22 and an unexpected distal breakpoint at 8q24.23 resulting in unbalanced translocation of a small 8q genomic region on the chromosome 16qter. The study of the 16qter region revealed that the 16q subtelomere was retained and the translocated material of distal 8q was juxtaposed. Moreover, molecular analyses showed that part of the translocated 8qter segment on der(16) was partially duplicated, inverted and that the rearrangement arose in the paternal meiosis. These findings emphasize the complexity of some only apparently simple chromosomal rearrangements and suggest a subtelomeric FISH approach to enhance diagnostic care when a cytogenetic terminal deletion is found.

Detection of BCR/ABL rearrangements in adult acute lymphoblastic leukemia using a highly sensitive interphase fluorescence in situ hybridization method (D-FISH).

INTRODUCTION: One hundred-and-six adult cases of acute lymphoblastic leukemia were prospectively investigated using a highly sensitive interphase fluorescence in situ hybridization assay which utilizes DNA probes that detect a double BCR/ABL fusion signal (D-FISH) in cells carrying the t(9;22) to evaluate the reliability and specificity of this method for the detection of the Ph translocation. The results were compared with those obtained in the same cases by conventional cytogenetics and by reverse-transcription polymerase chain reaction. MATERIALS AND METHODS: The study was performed using DNA probes that span the common breakpoints of the t(9;22) translocation and that detect a double BCR/ABL fusion in cells carrying this karyotypic anomaly, one on the abnormal chromosome 9 and one on the Ph chromosome. RESULTS: Interphase D-FISH detected a high number of rearranged cases (22/106) compared to conventional cytogenetics (15/106) and RT-PCR (21/106). CONCLUSION: Interphase D-FISH emerges as a reliable, fast and relatively inexpensive tool for the detection of BCR/ABL rearrangements in adult ALL patients at diagnosis. It has a sensitivity clearly higher than conventional karyotyping and it may prove also superior to that of RT-PCR in cases with unusual BCR/ABL breakpoints. Our results suggest that D-FISH might be considered as the initial test for the diagnosis of Ph+ adult ALL.