Prenatal diagnosis of a small supernumerary, XIST-negative, mosaic ring X chromosome identified by fluorescence in situ hybridization in an abnormal male fetus.
Marker or ring X [r(X)] chromosomes of varying size are often found in patients with Turner syndrome. Patients with very small r(X) chromosomes that did not include the X-inactivation locus (XIST) have been described with a more severe phenotype. Small r(X) chromosomes are rare in males and there are only five previous reports of such cases. We report the identification of a small supernumerary X chromosome in an abnormal male fetus. Cytogenetic analysis from chorionic villus sampling was performed because of fetal nuchal translucency thickness and it showed mosaicism 46,XY/47,XY,+r(X)/48,XY,+r(X),+r(X). Fluorescence in situ hybridizations (FISH) showed the marker to be of X-chromosome origin and not to contain the XIST locus. Additional specific probes showed that the r(X) included a euchromatic region in proximal Xq. At 20 weeks gestation, a second ultrasound examination revealed cerebral abnormalities. After genetic counselling, the pregnancy was terminated. The fetus we describe is the first male with a mosaic XIST-negative r(X) chromosome identified at prenatal diagnosis. The phenotype we observed was probably the result of functional disomy of the genes in the r(X) chromosome, secondary to loss of the XIST locus.
Le Caignec
C
C
Service de Génétique médicale, Centre Hospitalo-Universitaire, CHU Nantes, 9 quai Moncousu, 44093 Nantes cedex, France. lecaignec@hotmail.com
Boceno
M
M
Joubert
M
M
Winer
N
N
Aubron
F
F
Fallet-Bianco
C
C
Rival
J M
JM
D000015:Abnormalities, Multiple / Q000235:genetics*; D000025:Abortion, Eugenic; D000328:Adult; D015193:Chorionic Villi Sampling / Q000379:methods*; D041321:Chromosomes, Human, X; D020732:Cytogenetic Analysis; D004303:Dosage Compensation, Genetic; D005260:Female; D005817:Genetic Counseling; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D009030:Mosaicism / Q000235:genetics*; D009333:Neck / Q000000981:diagnostic imaging / Q000196:embryology; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D012303:Ring Chromosomes; D014463:Ultrasonography