Three unusual but cytogenetically similar cases with up to five different cell lines involving structural and numerical abnormalities of chromosome 18.
We report two prenatal and two postnatal diagnosed cases (the latter monozygotic twins) with ring chromosomes after GTG banding. All four, de novo r(18), cases turned out to be more complex after application of high-resolution molecular cytogenetics techniques such as use of fluorescence in situ hybridization, centromeric probes, multicolor banding, and locus-specific probes for chromosome 18. All four cases are mosaics involving chromosome 18 in up to five different cell lines, including 46,r(18); 46,dr(18); 47,r(18)x2; 46,mar(18); and 45,-18. Mosaicism sharing both numerical and structural anomalies is rare, but rings often appear as mosaics due to their mitotic instability. Overall, patients with ring chromosome 18 usually share clinical features of 18q- syndrome and, less frequently, those of 18p- syndrome. High-resolution molecular cytogenetics techniques were useful in the characterization of cases with dynamic mosaicism and in establishing the relationship between loss or gain of chromosomal material and the phenotype.
Carreira
Isabel M
IM
Laboratório de Citogenética e Centro de Neurociência e Biologia Celular, Faculdade de Medicina da Universidade de Coimbra, Coimbra, Portugal. i_marques@hotmail.com
Mascarenhas
Alexandra
A
Matoso
Eunice
E
Couceiro
Ana B
AB
Ramos
Lina
L
Dufke
Andreas
A
Mazauric
Marie
M
Stressig
Rüdiger
R
Kosyakova
Nadezda
N
Melo
Joana B
JB
Liehr
Thomas
T
D000015:Abnormalities, Multiple / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000235:genetics; D000328:Adult; D002460:Cell Line; D002869:Chromosome Aberrations; D002887:Chromosomes, Human, Pair 18; D020732:Cytogenetic Analysis; D004200:Diseases in Twins / Q000175:diagnosis* / Q000235:genetics; D005260:Female; D006801:Humans; D009030:Mosaicism; D011296:Prenatal Diagnosis / Q000379:methods*; D012303:Ring Chromosomes; D014430:Twins, Monozygotic; D014463:Ultrasonography