Prenatal diagnosis of partial monosomy 18p(18p11.2-->pter) and trisomy 21q(21q22.3-->qter) with alobar holoprosencephaly and premaxillary agenesis

A prenatal diagnosis of partial monosomy 18p(18p11.2-->pter) and trisomy 21q(21q22.3-->qter) in a fetus with alobar holoprosencephaly (HPE) and premaxillary agenesis (PMA) but without the classical Down syndrome phenotype is reported. A 27-year-old primigravida woman was referred for genetic counselling at 21 weeks' gestation due to sonographic findings of craniofacial abnormalities. Level II ultrasonograms manifested alobar HPE and median orofacial cleft. Cytogenetic analysis and fluorescence in situ hybridization (FISH) on cells obtained from amniocentesis revealed partial monosomy 18p and a cryptic duplication of 21q,46,XY,der(18)t(18;21)(p11.2;q22.3), resulting from a maternal t(18;21) reciprocal translocation. The breakpoints were ascertained by molecular genetic analysis. The pregnancy was terminated. Autopsy showed alobar HPE with PMA, pituitary dysplasia, clinodactyly and classical 18p deletion phenotype but without the presence of major typical phenotypic features of Down syndrome. The phenotype of this antenatally diagnosed case is compared with those observed in six previously reported cases with monosomy 18p due to 18;21 translocation. The present study is the first report of concomitant deletion of HPE critical region of chromosome 18p11.3 and cryptic duplication of a small segment of distal chromosome 21q22.3 outside Down syndrome critical region. The present study shows that cytogenetic analyses are important in detecting chromosomal aberrations in pregnancies with prenatally detected craniofacial abnormalities, and adjunctive molecular investigations are useful in elucidating the genetic pathogenesis of dysmorphism.     

Prenatal findings and molecular cytogenetic analyses of partial trisomy 12q (12q24.32-->qter) and partial monosomy 21q (21q22.2-->qter)

OBJECTIVES: To present the prenatal findings and molecular cytogenetic analyses of partial trisomy 12q and partial monosomy 21q, and a review of the literature. METHODS: Amniocentesis was performed at 23 gestational weeks in a 33-year-old woman because of abnormal sonographic findings. Amniocentesis revealed a derivative chromosome 21, or der(21), with a deletion on the region of 21q22.2 and an addendum of a small chromosomal segment of unknown origin. The maternal karyotype was subsequently found to be 46,XX,t(12;21)(q24.32;q22.2). Level II ultrasound showed microcephaly, micrognathia, a ventricular septal defect, and rocker-bottom feet. The pregnancy was terminated. A malformed infant was delivered without the phenotype of holoprosencephaly (HPE). Fluorescence in situ hybridization (FISH) and polymorphic DNA markers were used to investigate the involved chromosomal segments. RESULTS: FISH study showed the absence of the signal of 21q subtelomeric probe and the presence of the signal of 12q subtelomeric probe in the der(21).The fetal karyotype was 46,XY,der(21) t(12;21)(q24.32;q22.2)mat. Genetic marker analysis showed a deletion at 21q22.2 and a breakpoint between D21S156 (present) and D21S1245 (absent). The deleted segment was measured about 4.5 Mb encompassing the HPE critical region. CONCLUSIONS: Molecular genetic analyses help in determining the prenatally detected unbalanced cryptic translocation as well as parental balanced subtle translocation. A duplication of 12q24.32-->qter and a deletion of 21q22.2-->qter may be associated with prenatal sonographic findings of microcephaly, borderline ventriculomegaly and cerebellar hypoplasia, micrognathia, a ventricular septal defect, and rocker-bottom feet. Haploinsufficiency of the HPE critical region at 21q22.3 may not cause an HPE phenotype.     

Prenatal diagnosis of holoprosencephaly (HPE) in a fetus with a recombinant (18)dup(18q)inv(18)(p11.31q11.2)mat

Alobar holoprosencephaly (HPE) was identified by ultrasonography at 18 weeks' gestation in a fetus of a 29-year-old G2P0A1 woman. HPE has been described in association with various chromosomal anomalies. Amniocentesis was performed and a rearrangement of chromosome 18 resembling an isochromosome for the long arm of chromosome 18 was found. Subsequently, the mother was found to have a pericentric inversion of chromosome 18 with breakpoints at p11.31 and q11.2. The karyotype of the fetus was re-interpreted as 46,XX, rec(18)dup(18q)inv(18)(p11.31q11.2)mat. This is the first case of a parental inversion leading to a deficiency of 18p11.31 to 18pter associated with HPE.     

Prenatal diagnosis and molecular cytogenetic characterization of a pure ring chromosome 21 with a 4.657-Mb 21q22.3 deletion

ObjectiveWe present diagnosis and molecular cytogenetic characterization of a pure ring chromosome [r(21)] with a 4.657-Mb 21q22.3 deletion.Case reportA 44-year-old woman underwent amniocentesis at 18 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype 46,XX,r(21)(p11.2q22.3). Prenatal ultrasound findings were unremarkable. Simultaneous array comparative genomic hybridization (aCGH) analysis on uncultured amniocytes revealed a 4.657-Mb deletion at 21q22.3. The parental karyotypes were normal. The pregnancy was subsequently terminated, and a malformed fetus was delivered with facial dysmorphism and clinodactyly. Postnatal cytogenetic analysis of umbilical cord revealed a karyotype of 46,XX,r(21)(p11.2q22.3). aCGH analysis of umbilical cord revealed the result of arr 21q22.3 (43,427,188–48,084,156) × 1.0 with a 4.657-Mb 21q22.3 deletion encompassing 57 Online Mendelian Inheritance in Man (OMIM) genes including TRPM2, TSPEAR, COL18A1, COL6A1, COL6A2, LSS, PCNT, DIP2A, S100B and PRMT2. Metaphase fluorescence in situ hybridization (FISH) analysis of the umbilical cord fibroblasts confirmed a 21q22.3 deletion.ConclusionPrenatal diagnosis of an r(21) should include molecular cytogenetic characterization such as aCGH and FISH to determine the extent of the 21q22.3 deletion.     

Prenatal diagnosis and molecular cytogenetic characterization of a derivative chromosome der(18;18)(q10;q10)del(18)(q11.1q12.1)del(18)(q22.1q22.3) presenting as apparent isochromosome 18q in a fetus with holoprosencephaly

ObjectiveTo present prenatal diagnosis and molecular cytogenetic characterization of a derivative chromosome der(18;18)(q10;q10)del(18)(q11.1q12.1)del(18)(q22.1q22.3).Materials, Methods, and ResultsA 32-year-old woman was referred for genetic counseling of prenatally detected isochromosome 18q [i(18q)]. She had undergone amniocentesis at 19 gestational weeks because of a trisomy 18 risk of 1/39 derived from abnormally low levels of maternal serum unconjugated estriol, inhibin A, α-fetoprotein, and total β-human chorionic gonadotropin. Amniocentesis revealed a karyotype of 46,XX,i(18)(q10). Parental karyotypes were normal. Prenatal ultrasound showed alobar holoprosencephaly. Repeated amniocentesis was requested and performed at 21 gestational weeks. Array-comparative genomic hybridization analyses revealed a 14-Mb deletion of 18p11.32-p11.21, a 37.8-Mb duplication of 18q12.1-q22.1, and a 6.9-Mb duplication of 18q22.3-q23. Metaphase fluorescence in situ hybridization study showed the absence of an 18q12.1-specific probe signal in one arm and the absence of an 18q22.2-specific probe signal in the other arm of the derivative chromosome. Quantitative fluorescent polymerase chain reaction analysis determined a paternal origin of the derivative chromosome. The cytogenetic result was 46,XX,der(18;18)(q10;q10)del(18)(q11.1q12.1)del(18)(q22.1q22.3). The fetus postnatally manifested cebocephaly.ConclusionConcomitant monosomy 18p and trisomy 18q can be associated with holoprosencephaly and abnormal maternal serum screening results. Array-comparative genomic hybridization, fluorescence in situ hybridization, and quantitative fluorescent polymerase chain reaction are useful in genetic counseling of prenatally detected isochromosomes by providing information on the origin and genetic components of the isochromosome.     

Prenatal diagnosis and molecular cytogenetic characterization of mosaic ring chromosome 21 associated with low PAPP-A and low PlGF in the first-trimester maternal serum screening

ObjectiveWe present diagnosis and molecular cytogenetic characterization of mosaic ring chromosome 21 [r(21)].Case reportA 17-year-old, gravida 2, para 1, woman underwent amniocentesis at 17 weeks of gestation because of an abnormal result of the first-trimester maternal serum screening for Down syndrome with a free β-hCG level of 1.736 multiples of the median (MoM), a pregnancy associated plasma protein-A (PAPP-A) level of 0.275 MoM, a placental growth factor (PlGF) level of 0.281 MoM, a Down syndrome risk of 1:222 and a preeclampsia risk of 1:175. Cytogenetic analysis of cultured amniocytes revealed the result of 46,XX,r(21) (p12q22.3)[19]/45,XX,-21[13]. Array comparative genomic hybridization (aCGH) analysis of cultured amniocytes revealed the result of arr [GRCh37] 21q11.2q22.2 (15,485,008–40,625,594) × 1～2, 21q22.2q22.3 (40,703,792–46,682,184) × 2～3, 21q22.3 (46,761,631–48,084,156) × 1, consistent with mosaic monosomy 21 and r(21) (p12q22.3). The pregnancy was subsequently terminated, and a malformed fetus was delivered with low-set ears and hypotelorism. Postnatal cytogenetic analysis revealed a karyotype of 46,XX,r(21) (p12q22.3)[30]/45,XX,-21[8]/46,XX,idic r(21) (p12q22.3)[2] in the cord blood, 46,XX,r(21) (p12q22.3)[34]/45,XX,-21[6] in the skin, 46,XX,r(21) (p12q22.3)[37]/45,XX,-21[3] in the umbilical cord and 46,XX,dup(21) (q22.2q22.3)[32]/46,XX,r(21) (p12q22.3)[8] in the placenta. aCGH analysis of cord blood revealed the result of arr 21q11.2q22.2 (15,499,847–40,662,581) × 2.3, arr 21q22.2q22.3 (40,703,792–46,682,184) × 3.6, arr 21q22.3 (46,761,632–48,090,317) × 1, consistent with mosaic duplication of 21q11.2-q22.2 and 21q22.2-q22.3, and a 1.33-Mb 21q22.3 deletion encompassing the genes of COL18A1, SLC19A1, PCBP3, COL6A1, COL6A2, FTCD, LSS, MCM3AP, YBEY, PCNT, DIP2A, S100B and PRMT2.ConclusionMosaic r(21) at amniocentesis may be associated with monosomy 21, idic r(21) and dup(21), and low PAPP-A and low PlGF in the first-trimester maternal serum screening.     

Prenatal diagnosis of trisomy 4p: a new locus for holoprosencephaly?

Trisomy of the short arm of chromosome 4 is a well-known syndrome, and several observations have been made in the last 30 years. Herein, we report a new observation of trisomy 4p in a fetus with a semi-lobar holoprosencephaly (HPE), dysmorphic features and multiple malformations. The diagnosis of HPE was made, at 33 weeks' gestation, on the fetus of a healthy G1P0 woman. Amniocentesis was performed for chromosome analysis and additional material was found on a chromosome 22. The couple elected to terminate the pregnancy and fetal examination was realized. Conventional and molecular cytogenetic studies were performed on the fetus and the parents, which showed that the additional material found on one chromosome 22 corresponded to the short arm of chromosome 4 and therefore led us to establish a diagnosis of trisomy 4p inherited from the malsegregation of a paternal translocation t(4;22)(q12;q11.1). The etiology of HPE is very heterogeneous; it includes non-genetic factors such as maternal diabetes and genetic causes. HPE cases have been described in association with many chromosomal anomalies, trisomy 13 being the most frequent. However, to our knowledge, HPE has never been previously reported in association with a trisomy involving solely the short arm of chromosome 4.     

Prenatal diagnosis of mosaic ring chromosome 22 associated with cardiovascular abnormalities and intrauterine growth restriction

OBJECTIVES: To present the prenatal diagnosis and perinatal findings of mosaic ring chromosome 22. CASE: Amniocentesis was performed at 18 gestational weeks because of an advanced maternal age. Cytogenetic analysis of the cultured amniotic fluid cells revealed mosaicism for ring chromosome 22, 45,XX,-22[6]/46,XX,r(22)(p13q13.31)[15]. Abnormal fetal sonographic findings included small for gestational age, a ventricular septal defect, and truncus arteriosus. The pregnancy was terminated. Additional phenotypic findings included hypertelorism, epicanthal folds, and abnormal ears. Cytogenetic analysis of the cord blood lymphocytes revealed a complex mosaic karyotype, 45,XX,-22[7]/46,XX,r(22)(p13q13.31)[82]/46,XX,idic r(22)(p13q13.31;p13q13.31)[11]. Cytogenetic analysis of the hepatocytes also revealed mosaic r(22) with mosaicism for idic r(22) and monosomy 22. The deletion of distal 22q and the duplication of 22q11.2 on idic r(22), and the distal 22q deletion on r(22) were demonstrated by fluorescent in situ hybridization (FISH) analysis using 22q terminal probes at 22q13 and a DiGeorge syndrome critical region probe at 22q11.2. The breakpoint on distal 22q13 and the extent of the duplication of 22q on idic r(22) was determined by examining polymorphic markers specific for chromosome 22 using quantitative fluorescent polymerase chain reaction assays. The chromosomal aberration was of maternal origin. CONCLUSION: Molecular and FISH studies allow a better delineation of some prenatally detected aneuploidy syndromes and help elucidate the genetic pathogenesis. Fetuses having mosaic r(22) with a low level mosaicism for r(22) duplication/deletion may present cardiovascular abnormalities and intrauterine growth restriction on prenatal ultrasound.     

Prenatal diagnosis of a fetus with distal 10q trisomy.

Distal 10q trisomy is a well-defined but rare syndrome. Most cases are diagnosed in infancy or in childhood and rarely include prenatal findings. We present a case of fetal distal 10q trisomy with abnormal prenatal sonographic findings. A 19-year-old primigravida was referred for genetic counselling at 18 gestational weeks because her husband had a familial history of congenital anomalies. Genetic amniocentesis was thus performed and showed fetal distal 10q trisomy (10q24.1-->qter), 46,XX,der(22)t(10;22)(q24.1;p11.2)pat, resulting from paternal t(10;22) reciprocal translocation. Level II ultrasonograms further demonstrated bilateral hydronephrosis, ventricular septal defect and facial dysmorphism ascertained by three-dimensional ultrasound. The pregnancy was terminated at 22 gestational weeks. Post-mortem autopsy confirmed the sonographic findings. We suggest that abnormal prenatal sonographic findings such as cardio-vascular, renal and facial malformations should alert cytogeneticists to search for subtle chromosomal abnormalities.     

Neuroblastoma in a dysmorphic girl with a partial duplication of 2p caused by an unbalanced translocation

A 1-year-old female child with multiple dysmorphic features including microcephaly, hypertelorism, a short philtrum, low set ears, a narrow high arched palate, micrognathia and growth retardation was found to have a de novo chromosome abnormality including a partial duplication of the short arm of chromosome 2 and a partial deletion of the long arm of chromosome 17. The clinical features of the case shared many similarities to previous reports of trisomy 2p. Three years later, ecchymotic spots appeared around the left ocular region. Further clinical and pathological examination confirmed the diagnosis of a neuroblastoma. This is the first case of an unbalanced translocation, 46, XX, der (17), t (2; 17) (p23; q25), showing the development of a neuroblastoma in addition to the dysmorphic features. We suggest that trisomy 2p including the N-myc proto-oncogene may have predisposed the patient to the development of a neuroblastoma.     

Prenatal diagnosis of a fetus affected with Down syndrome and deletion 1p36 syndrome by fluorescence in situ hybridization and spectral karyotyping

OBJECTIVE: A fetus having partial trisomy of the distal part of chromosome 21q due to a de novo translocation is reported here. METHOD: A 29-year-old woman received amniocentesis at 18 weeks of gestation because of abnormal ultrasound findings including bilateral choroid plexus cysts, atrioventricular septal defects, rocker-bottom feet, and possible hydrocephalus. RESULTS: Cytogenetic analysis revealed 46,XY, add(1)(p36.3), in which an additional material of unknown origin was attached to one of the terminal short arms of chromosome 1. Parental blood studies showed normal karyotypes in both parents. Spectral karyotyping was then performed and the origin of the additional material locating at chromosome 1p was found to be from chromosome 21. Conventional fluorescence in situ hybridization analysis was also used and confirmed the spectral karyotyping findings by use of a chromosome 21 specific painting probe, a locus specific probe localized within bands 21q22.13-q22.2 and a 21q subtelomeric probe. A hidden Down syndrome caused by a de novo translocation in this fetus was therefore diagnosed and the karyotype was designated as 46,XY, der(1)t(1;21)(p36.3;q22.1).ish der(1)(WCP21+, LSI 21+, 1pTEL-, 21q TEL+) de novo. Clinical features of the 1p36 deletion syndrome are also reviewed and may contribute to some features of this fetus. Termination of pregnancy was performed at 20 weeks of gestation. CONCLUSION: To our knowledge, our case appears to be the first to have partial monosomy 1p and partial trisomy 21q caused by de novo translocation being diagnosed prenatally.     

De novo monosomy 9p24.3-pter and trisomy 17q24.3-qter characterised by microarray comparative genomic hybridisation in a fetus with an increased nuchal translucency

OBJECTIVES: Increased nuchal translucency (NT) during the first trimester of pregnancy is a useful marker to detect chromosomal abnormalities. Here, we report a prenatal case with molecular cytogenetic characterisation of an abnormal derivative chromosome 9 identified through NT. METHODS: Amniocentesis was performed because of an increased NT (4.4 mm) and showed an abnormal de novo 46,XX,add(9)(p24.3) karyotype. To characterise the origin of the small additional material on 9p, we performed a microarray comparative genomic hybridisation (microarray CGH) using a genomic DNA array providing an average of 1 Mb resolution. RESULTS: Microarray CGH showed a deletion of distal 9p and a trisomy of distal 17q. These results were confirmed by FISH analyses. Microarray CGH provided accurate information on the breakpoint regions and the size of both distal 9p deletion and distal 17q trisomy. The fetus was therefore a carrier of a de novo derivative chromosome 9 arising from a t(9;17)(p24.3;q24.3) translocation and generating a monosomy 9p24.3-pter and a trisomy 17q24.3-qter. CONCLUSION: This case illustrates that microarray CGH is a rapid, powerful and sensitive technology to identify small de novo unbalanced chromosomal abnormalities and can be applied in prenatal diagnosis.     

Molecular cytogenetic characterization of a de novo unbalanced translocation leading to trisomy 17q25-->qter and monosomy 18p11.3-->pter in a girl with dysmorphic features

An 18-year-old, gravida 1 underwent percutaneous umbilical blood sampling (PUBS) because of positive triple screen, oligohydramnios and markedly short fetal bones. Chromosome analysis showed an abnormal chromosome 18 with unidentified chromatin at the end of the p-arm. Parental karyotypes were normal. FISH analyses with wcp18 showed additional material of unknown origin on the derivative chromosome 18. Further FISH analysis with subtelomeric probes showed normal signals for the long arm of chromosome 18 (18q23) while no signals were observed for the short arm (18p11.32). These findings were confirmed using a YAC probe from the short arm of 18. The infant was delivered at 30 weeks of gestation. At age 3 months, she was developmentally delayed and has multiple dysmorphic features. Further molecular cytogenetic studies including M-FISH and subtelomere probes showed that the additional material on chromosome 18 consisted of the distal 17q25-->qter region. Based on these studies the karyotype has been interpreted as 46,XX,der(18)t(17;18)(q25;p11.32). To the best of our knowledge, this is the first report of partial monosomy 18p and partial trisomy 17q in a patient with no major CNS malformations. This case shows the importance of molecular cytogenetic techniques in detailed characterization of de novo chromosome rearrangements.     

Prenatal diagnosis of partial trisomy 3p(3p23-->pter) and monosomy 7q(7q36-->qter) in a fetus with microcephaly alobar holoprosencephaly and cyclopia.

We report the prenatal diagnosis of partial trisomy 3p(3p23-->pter) and monosomy 7q(7q36-->qter) in a fetus with microcephaly, alobar holoprosencephaly and cyclopia. A 26-year-old primigravida woman was referred for genetic counselling at 23 gestational weeks due to sonographic findings of intra-uterine growth retardation and cranio-facial abnormalities. Level II ultrasonograms further demonstrated alobar holoprosencephaly, a proboscis above the eye and a single median orbit consistent with cyclopia. Genetic analysis and fluorescence in situ hybridization on cells obtained from amniocentesis showed distal 3p trisomy (3p23-->pter) and 7q36 deletion, 46,XX,der(7)t(3;7)(p23;q36), resulting from a paternal t(3;7) reciprocal translocation. The pregnancy was terminated. Autopsy further confirmed the presence of arrhinencephaly, agenesis of the corpus callosum and a single ventricle of the brain. The phenotype of this antenatally diagnosed case is compared with those observed in 10 previously reported cases with simultaneous occurrence of partial trisomy 3p and terminal deletion 7q. All cases are associated with severe forms of holoprosencephaly and facial dysmorphism. This delineates an autosomal imbalance syndrome or a dosage effect involving duplication of distal 3p/deficiency of terminal 7q and dysmorphogenesis of the forebrain and mid-face.     

Rapid diagnosis of trisomy 18 of maternal origin by quantitative fluorescent polymerase chain reaction analysis following tissue culture failure for conventional cytogenetic analysis in a fetus with holoprosencephaly,ventricular septal defect,arthrogryposis of bilateral wrists and aplasia of the thumbs

ObjectiveWe present rapid diagnosis of trisomy 18 of maternal origin by quantitative fluorescent polymerase chain reaction (QF-PCR) analysis following tissue culture failure for conventional cytogenetic analysis in a fetus with holoprosencephaly (HPE), ventricular septal defect (VSD), arthrogryposis of bilateral wrists and aplasia of the thumbs.Case reportA 22-year-old, primigravid woman was referred for first-trimester ultrasound screening at 13 weeks of gestation, and the fetus was found to have HPE and VSD. The pregnancy was subsequently terminated at 14 weeks of gestation, and a malformed fetus was delivered with cebocephaly, arthrogryposis of bilateral wrists and aplasia of the thumbs. The umbilical cord and placental tissues were collected for genetic analysis. However, tissue culture failure for conventional cytogenetic analysis occurred because of contamination. QF-PCR analysis using the polymorphic DNA markers of D18S1369 (18q12.2) and D18S1361 (18q22.3) confirmed trisomy 18 of maternal origin.ConclusionQF-PCR analysis is useful for rapid confirmation of trisomy 18 and the parental origin when tissue culture failure for conventional cytogenetic analysis occurs in pregnancy suspicious of fetal trisomy 18.     

Familial 18p deletion syndrome and 18p partial trisomy inherited from a mother with balanced translocation

18p deletion syndrome can be easily missed in a clinical setting as the facial features, though typical, can be overlooked and the other features including growth retardation and learning disability are nonspecific. We present a family in which the proband has 18p deletion syndrome. The proband performed better on verbal skills than on performance tasks on intelligence testing. She had attention-deficit hyperactivity disorder, which required medication and behavioral therapy. Subsequent cytogenetic analysis in her elder brother who presented with learning difficulties showed partial trisomy 18p and the maternal karyotype is 46, XX,(15;18)(p11.2;p11.2). This is the first report of a family with a balanced maternal translocation resulting in 18p deletion in one sibling and 18p partial trisomy in the other.     

Duplication of the Down syndrome critical region does not predict facial phenotype in a baby with a ring chromosome 21

Ring chromosomes represent a rare type of chromosomal anomaly that can lead to multiple malformations. Although rings may occur with any chromosome, ring chromosome 21 is of particular interest due to the association of this chromosome with Down syndrome. Individuals with a ring chromosome 21, containing duplicated material, typically have a phenotype consistent with Down syndrome. We report an infant with a ring chromosome 21 containing a duplication of most of the long arm, including the Down syndrome critical region [46,XX,r(21)(p11.2q22.3)]. Fluorescence in situ hybridization analyses of the ring showed one chromosome 21 centromere, two copies each of the AML1 gene (q22) and the Down syndrome critical region, and deleted subtelomeric material. The patient has some Down syndrome characteristics including a high arched palate, a secundum atrial septal defect, and duodenal stenosis, but lacks the typical Down syndrome facial features, nuchal folds, and hand/foot anomalies. The phenotype of this patient supports the hypothesis that the duplication of the Down syndrome critical region alone is not sufficient to recapitulate the classical Down syndrome craniofacial phenotype.     

Two unusual chromosome aberrations ascertained by sonographic anomalies

We describe two cases of sonographic abnormalities associated with unusual chromosomal aberrations. Case 1 presented with a cystic hygroma at 12 weeks' gestation. Cytogenetic analysis revealed an unbalanced complex chromosome rearrangement implicating chromosomes 6, 13 and 21 (karyotype: 47,XX,t(6;21;14)(q14;q21;q21)mat,+21) and corresponding to a complete trisomy 21. This anomaly resulted from malsegregation of a maternal balanced three-way translocation. For case 2, an alobar holoprosencephaly was identified by ultrasonography at 23 weeks' gestation. Chromosomal analysis showed a recombinant rec (13), dup q chromosome, secondary to unequal crossing-over of a paternal pericentric inversion of chromosome 13, giving rise to partial trisomy 13q (karyotype: 46,XX,rec(13)dup(13q)inv(13)(p11q21)pat). These two cases illustrate the role of ultrasound in leading to detection not only of foetal chromosomal aberrations but also of rare balanced chromosomal rearrangements presented by one of the two parents.     

Prenatal detection of complex chromosomal aberrations using advanced molecular cytogenetic techniques

OBJECTIVE: This study aimed to identify a marker chromosome and characterize the short arm of a derivative chromosome 5 in a foetus with the following karyotype: mos 47,XX,del(5)(p?),+i(5)(p10)[50]/48,XX,del(5)(p?),+i(5)(p10),+mar[25]. METHOD: Amniocentesis was performed in the 26th week of pregnancy because of ultrasound abnormalities (polyhydramnion and decreased amount of gastric filling). All classic banding techniques were performed. FISH and microdissection combined with reverse painting were used to reveal the exact origin of the marker and any extra material on the deleted chromosome 5p. The parents decided to continue the pregnancy and we compared the clinical features of the child born in week 34 with data from the literature on trisomy 5p. The possible contribution of trisomy of the centromeric region of chromosome 8 and trisomy 8p23.3-->8pter to this clinical picture was evaluated. RESULTS: GTG banding showed one normal and two aberrant chromosomes 5 [del(5)(p?) and i(5)(p10)] in all the cells examined. Furthermore, a supernumerary marker chromosome was present in approximately 30% of the cells. The marker was CBG positive and positive with the pancentromere probe, but dystamicinA/DAPI negative. It did not contain NOR-positive satellites. FISH proved this marker to be derived from the centromeric region of chromosome 8. MicroFISH disclosed the aberrant chromosome 5 as der(5)t(5;8)(p10;p23.3). The parent's karyotypes were normal. The baby showed the characteristic features of trisomy 5p syndrome. She died at the age of 15 days after cardiorespiratory arrest. CONCLUSION: The karyotype was interpreted as mos 47,XX,add(5)(p10).rev ish der(5)t(5;8)(p10;p23.3),+i(5)(p10) (WCP5+,D5S23+)[50]/48,XX,add(5)(p10).rev ish der(5)t(5;8)(p10;p23.3),+i(5)(p10)(WCP5+,D5S23+),+mar.ish 8(p10q10)(D8Z2+,WCP8-)[25]. Therefore, the baby had complete trisomy 5p, with trisomy of the distal part of 8p and of the centromeric region of chromosome 8. The clinical significance of de novo marker chromosomes is a major problem in prenatal counselling. Molecular cytogenetic tools such as FISH and microFISH are indispensable for characterizing markers and determining the breakpoints more precisely in deleted chromosomes.     

Prenatal diagnosis and molecular cytogenetic analysis of partial monosomy 10q (10q25.3-->qter) and partial trisomy 18q (18q23-->qter) in a fetus associated with cystic hygroma and ambiguous genitalia

OBJECTIVES: To present the prenatal diagnosis and molecular cytogenetic analysis of a fetus with nuchal cystic hygroma and ambiguous genitalia. CASE AND METHODS: Amniocentesis was performed at 16 weeks' gestation because of the abnormal fetal sonographic finding of a large septated nuchal cystic hygroma. Genetic amniocentesis revealed a terminal deletion in the long arm of chromosome 10. The paternal karyotype was subsequently found to be 46,XY,t(10;18)(q25.3;q23). The maternal karyotype was normal. The pregnancy was terminated. A hydropic fetus was delivered with a septated nuchal cystic hygroma and ambiguous genitalia. Fluorescence in situ hybridization (FISH), microarray-based comparative genomic hybridization (CGH), and polymorphic DNA markers were used to investigate the involved chromosomal segments. RESULTS: FISH study showed absence of the 10q telomeric probe and presence of the 18q telomeric probe in the derivative chromosome 10. Microarray-based CGH analysis showed loss of distal 10q and gain of distal 18q. Polymorphic DNA marker analysis determined the breakpoints. The fetal karyotype was 46,XY,der(10)t(10;18)(q25.3;q23)pat. The chromosome aberration resulted in partial monosomy 10q (10q25.3-->qter) and partial trisomy 18q (18q23-->qter). CONCLUSIONS: The present case provides evidence that partial monosomy 10q (10q25.3-->qter) with partial trisomy 18q (18q23-->qter) can be a genetic cause of fetal cystic hygroma and ambiguous genitalia. Cytogenetic analysis for prenatally detected structural abnormalities may detect unexpected inherited chromosome aberrations.