2008-05-07-09 Partial trisomy 6q associated with hydrops and early fetal malformations © Molina www.thefetus.net/
Partial trisomy 6q associated with hydrops and early fetal malformations
Complejo Hospitalario Materno Insular Gran Canaria. Spain. (*) Servicio de Obstetricia y Ginecología. (**) Servicio de Genética.
Correspondence to: Andrés Arencibia Molina, Paseo de Lugo nº 16, Piso Primero (3), Las Palmas de Gran Canaria, Apartado 35004. España.
A 29 year-old woman (G3P2) presented to our department at 12 weeks of pregnancy.
Her first pregnancy had an uneventful course and she gave birth to a healthy neonate. During her second pregnancy an intrauterine growth restricted fetus was discovered at 34th week. The pregnancy was terminated by emergency caesarean section due to reversed end-diastolic flow at the level of umbilical artery and abnormal cardiotocography with flat tracing and late decelerations. A hydropic newborn was delivered and died early after delivery, but the parents declined autopsy and no genetic studies were performed at that time.
She presented at 12 weeks of her third pregnancy for ultrasound examination and biochemical testing. The ultrasound examination revealed an enlarged nuchal translucency (7.5 mm) with enlargement of the skin edema up to the sacral and pericranial regions (Images 1, 2). Abnormal positions of the humerus, ulna and radius, abnormal movements of the elbow joints in flexion, extension, pronation and supination, abnormal wrist joints movements, and abnormal angulations and deformities of both hands were also found. Dislocations of the hips, knees and ankle joints were suspected because of their abnormal movements during the ultrasound study. Careful color Doppler cardiac scan at 14th week discovered an atrioventricular septal defect (Image 3) and a reversed flow at the level of the ductus venosus. The maternal serological tests (Rubeola, Syphilis, Toxoplasmosis, Cytomegalovirus and Parvovirus B19) were negative. An invasive chorionic villous sampling was done at 13th week. A quantitative fluorescence chain polymerase chain reaction of 13, 18, 21, X and Y chromosomes (QF-PCR) as well as the full karyotype revealed 46, XX, der(18)t(6;18)(q23;p11.3)pat karyotype, with duplications or partial trisomy of the 6th chromosome (q23;qter). The parents opted for the termination of the pregnancy. Subsequently a parental chromosomal examinations revealed a balanced translocations in the father`s karyotype between one of the long arms of the chromosome 6 and a short arm of the 18th chromosome, resulting in 46, XY, t(6,18) (q23;p11.3) karyotype.
A combination of nuchal translucency with the maternal serum PAPP-A and B-hCG has a detection rate of approximately 90% for trisomies 21,18 and 13 with a 5% false positive rate. In our case, an increased nuchal translucency (7,5 mm) was associated with a genetic syndrome where the previous history was very important to make up the correct diagnosis. Partial trisomy 6q is an extremely rare chromosomal disorder in which the distal part of the long arm (q) of the 6th chromosome is present three times in cells of the body [1,2]. Craniofacial malformations, webbed neck, abnormal flexion or extension of joints (joint contractures), and cardiac abnormalities may be present. In our case the partial trisomy 6q was a result of the balanced translocation of one of the parents, which was previously described in literature [3,4]. This explains the recurrent fetal hydrops and poor perinatal outcome in our case.
Images 1, 2: 12 weeks of pregnancy; the images show sagittal (image 1) and transverse (image 2) scans of the fetal nuchal region with noticeably increased nuchal translucency thickness.
Images 3: 14 weeks of pregnancy; color Doppler transverse scan of the fetal heart with atrioventricular septal defect.
Video 1: Video shows the fetus at 14 weeks of pregnancy with prominent nuchal edema.
1. Fitch N: Partial trisomy 6. clin Genet 14:181-185, 1978.
2. Berheim A et al. Partial trisomy 6. Hum Genet 48: 13-16, 1979.
3. Rothlisberger B et al. Essentialy pure partial (6)(p23--->pter) in two brothers due to maternal t(6;17)(p23;p13.3).Am J med Genet 85:389-394. 1999.
4. Runick-Schoneborn S et al. Partial trisomy 6p from a de novo translocation (6:18) with variable mosaicism in different tissues. Clin Genet 85. 126-199. 1997.