Chromosomal breakpoints characterization of two supernumerary ring chromosomes 20.

The occurrence of an additional ring chromosome 20 is a rare chromosome abnormality, and no common phenotype has been yet described. We report on two new patients presenting with a supernumerary ring chromosome 20 both prenatally diagnosed. The first presented with intrauterine growth retardation and some craniofacial dysmorphism, and the second case had a normal phenotype except for obesity. Conventional cytogenetic studies showed for each patient a small supernumerary marker chromosome (SMC). Using fluorescence in situ hybridization, these SMCs corresponded to ring chromosomes 20 including a part of short and long arms of chromosome 20. Detailed molecular cytogenetic characterization showed different breakpoints (20p11.23 and 20q11.23 for Patient 1 and 20p11.21 and 20q11.21 for Patient 2) and sizes of the two ring chromosomes 20 (13.6 Mb for case 1 and 4.8 Mb for case 2). Review of the 13 case reports of an extra r(20) ascertained postnatally (8 cases) and prenatally (5 cases) showed varying degrees of phenotypic abnormalities. We document a detailed molecular cytogenetic chromosomal breakpoints characterization of two cases of supernumerary ring chromosomes 20. These results emphasize the need to characterize precisely chromosomal breakpoints of supernumerary ring chromosomes 20 in order to establish genotype-phenotype correlation. This report may be helpful for prediction of natural history and outcome, particularly in prenatal diagnosis.

Molecular cytogenetic characterization of a 4p15.1-pter duplication and a 4q35.1-qter deletion in a recombinant of chromosome 4 pericentric inversion.

To date, 10 cases of recombinant of chromosome 4 pericentric inversion involving sub-bands p14p15 and q35 have been described. We report on the first case analyzed using array-CGH in a female infant presenting psychomotor and growth retardation, facial anomalies, axial hypotonia, short neck, wide spaced nipples and cardiac defects. Conventional karyotype associated to FISH revealed a recombinant chromosome 4 with partial 4p duplication and 4q deletion derived from a paternal pericentric inversion. Array-CGH allowed us to precise rec4 breakpoints: the proposita carried a small 4.82-4.97 Mb 4q35.1 terminal deletion and a large 35.3-36.7 Mb 4p15.1 terminal duplication. Duplications of the distal 2/3 of short arm of chromosome 4 give rise to recognizable craniofacial features but no specific visceral malformation. A contrario small terminal 4q deletions are associated with cardiac defects. This case and review of literature suggest that two genes ArgBP2 and PDLIM3, located at 4q35.1 and both involved in cardiac and muscle development, could be responsible for cardiac defects observed in terminal 4q35.1 deletions.

[Risk of missed diagnosis of 22q11.2 deletion in a fetal cardiac conotruncal malformation when another chromosomal abnormality is detected]. / Risque d'absence de diagnostic prénatal d'une délétion 22q11.2 associée à une autre anomalie chromosomique dans une malformation cardiaque conotroncale.

We present a rare case of prenatal diagnosis of two de novo chromosome structural rearrangements including a translocation (1;3) associated with a 22q11.2 deletion. The amniocentesis was performed because the systematic ultrasound examination revealed: right aortic cross with double aortic arch, with normal size of aorta and pulmonary artery. Our report emphasises that 22q11.2 deletion must be looked for when a fetal cardiac conotruncal malformation is diagnosed, even in the presence of another chromosomal abnormality. In prenatal diagnosis, this can have implication for patient management and genetic counselling.

Terminal 14q32.33 deletion: genotype-phenotype correlation.

We report on a female infant presenting with psychomotor retardation and facial dysmorphism. Cytogenetic studies showed an abnormal chromosome 14 with ectopic NOR sequences at the extremity of the long arm with a terminal 14q32.33 deletion. Review of the eight cases with pure terminal 14q32.3 deletions described to date documented that our observation is the smallest terminal 14q deletion ever reported. Thus, genotype-phenotype correlation allows us to delimit the critical region for mental retardation, hypotonia, epi-telecanthus, short bulbous nose, long philtrum, thin upper lip, and small mouth observed in 14 qter deletions to the subtelomeric 1.6 Mb of chromosome 14.