Li Feng Chen

Mosaic Trisomy 7 at Amniocentesis: Prenatal Diagnosis and Molecular Genetic Analyses

OBJECTIVEnTo present prenatal diagnosis and molecular genetic analyses of mosaic trisomy 7.nnnMATERIALS, METHODS AND RESULTSnA 38-year-old primigravid woman underwent amniocentesis at 19 weeks of gestation because of her advanced maternal age. Amniocentesis revealed a karyotype of 47,XY,+7[26]/46, XY[16]. Repeated amniocentesis at 21 weeks of gestation revealed a karyotype of 47,XY,+7[20]/46,XY[17]. Simultaneous cordocentesis revealed a karyotype of 46,XY in 100/100 cultured lymphocytes. Polymorphic DNA marker analyses of uncultured amniocytes and cord blood revealed a diallelic pattern with seemingly equal biparental inheritance of chromosome 7. Repeated cordocentesis and chorionic villus sampling at 23 weeks of gestation revealed a karyotype of 47,XY,+7[2]/46,XY[66] in cord blood and a karyotype of 47,XY,+7 in 24/24 cultured chorionic villi cells. Level II ultrasonography was normal. At 40 weeks of gestation, a 2,708 g normal male baby was delivered. The peripheral blood had a karyotype of 46,XY in 100/100 lymphocytes. Molecular analyses of placenta, urine, buccal swab, and peripheral blood revealed a diallelic pattern and seemingly equal biparental inheritance of chromosome 7 in all tissues. At 3 months of age, he manifested hypopigmented skin and inguinal hernia, but showed normal growth and mental development. Fluorescence in situ hybridization analysis of inguinal hernia sac tissue revealed that 19/100 (19%) of nuclei had three chromosome 7 signals.nnnCONCLUSIONnMosaic trisomy 7 at amniocentesis may be derived from a cell culture artifact from an undetected low level of trisomy 7 mosaicism in uncultured amniocytes, and can be associated with favorable fetal outcome if the blood has a normal karyotype or a very low level of mosaicism and if uniparental disomy for chromosome 7 is excluded.

Unbalanced reciprocal translocations at amniocentesis

OBJECTIVEnTo present perinatal findings, modes of ascertainments, and modes of segregation in unbalanced reciprocal translocations detected at amniocentesis.nnnMATERIALS AND METHODSnBetween January 1987 and July 2010, 40 cases with unbalanced reciprocal translocations were diagnosed by amniocentesis at Mackay Memorial Hospital, Taipei, Taiwan. The 40 cases originated from 29 families; 21 families with one case, 7 families with two cases, and 1 family with five cases.nnnRESULTSnOf 40 cases, 33 (82.5%) presented fetal ultrasound abnormalities and 7 (17.5%) presented no ultrasound abnormalities. Of 40 cases, 36 (90%) had a segregation mode of adjacent-1 2:2 segregation, 3 (7.5%) had a segregation mode of 3:1 segregation with tertiary trisomy, and 1 (2.5%) had a segregation mode of 3:1 segregation with tertiary monosomy. Of 29 families, 7 (24.1%) had de novo translocations and 22 (75.9%) had inherited translocations. In seven de novo cases, the main modes of ascertainments included abnormal ultrasound findings (n = 5) and advanced maternal age (n = 2). In 22 inherited families, the main modes of first ascertainment included abnormal ultrasound findings (n = 8), a previous aneuploid child (n = 8), advanced maternal age (n = 4), parental carrier status (n = 1), and abnormal maternal serum screening results (n = 1). Among 22 inherited families, 9 (40.9%) had a known parental carrier status, but 13 (59.1%) were unaware of parental carrier status at amniocentesis.nnnCONCLUSIONnUnbalanced reciprocal translocations detected at amniocentesis are frequently associated with abnormal ultrasound findings. Prenatal diagnosis of an unbalanced translocation may incidentally detect a balanced translocation in the family. Prenatal diagnosis of fetal structural abnormalities should alert structural chromosome rearrangements and prompt cytogenetic analysis of the fetus and parents if necessary.

Prenatal diagnosis and molecular cytogenetic characterization of a small supernumerary marker chromosome derived from chromosome 8.

OBJECTIVEnTo present prenatal diagnosis and molecular cytogenetic characterization of a small supernumerary marker chromosome (sSMC) derived from chromosome 8 by multiplex ligation-dependent probe amplification (MLPA), fluorescence in situ hybridization (FISH), spectral karyotyping (SKY) and array comparative genomic hybridization (aCGH).nnnCASE REPORTnA 42-year-old woman, gravida 6, para 3, underwent amniocentesis at 19 gestational weeks because of advanced maternal age. Amniocentesis revealed a de novo ring-shaped sSMC in all 13 colonies of the amniocytes. The karyotype was 47,XY,+mar. The MLPA showed duplications of 8p11.21-specific probes. At 24 gestational weeks, level II ultrasound revealed a left multicystic kidney in the fetus. Other internal organs were unremarkable. Repeat amniocentesis revealed a karyotype of 47,XY,+mar[25]/46,XY[2]. The sSMC was characterized by SKY and FISH, which showed a chromosome 8 origin of the sSMC. Oligonucleotide-based aCGH demonstrated a 4.4-Mb duplication of 8p11.21q11.1 [arr cgh 8p11.21q11.1 (42,637,263-47,062,180)×3]. The karyotype was 47,XY,+r(8) (p11.21q11.1)[25]/46,XY[2]. Polymorphic DNA marker analysis revealed no uniparental disomy for chromosome 8. The woman elected to continue the pregnancy and at 34 gestational weeks, a 1,820 g male baby without craniofacial dysmorphism was delivered. At the age of 1 month, the infant was apparently normal except for left multicystic kidney disease and mild ventriculomegaly.nnnCONCLUSIONnMLPA, SKY and aCGH are helpful in genetic counseling of prenatally detected sSMCs by providing the immediate information on the origin and the genetic contents of the sSMC.

Prenatal diagnosis and molecular cytogenetic characterization of mosaicism for a small supernumerary marker chromosome derived from ring chromosome 4

OBJECTIVEnTo present prenatal diagnosis and molecular cytogenetic characterization of mosaicism for a small supernumerary marker chromosome (sSMC) derived from ring chromosome, or r(4) by spectral karyotyping (SKY), fluorescence in situ hybridization (FISH), and array comparative genomic hybridization (aCGH).nnnMATERIALS, METHODS, AND RESULTSnA 37-year-old, primigravid woman underwent amniocentesis at 18 weeks of gestation because of advanced maternal age. Amniocentesis revealed a de novo ring-shaped sSMC in 16 of 31 amniocyte colonies. The parental karyotypes were normal. Level II ultrasound findings were unremarkable. Repeated amniocentesis revealed a karyotype of 47,XX,+mar[17]/46,XX[19]. The sSMC was characterized by SKY and FISH, which showed a chromosome 4 origin of the sSMC. aCGH demonstrated a 21.7-Mb gain in the gene dosage encompassing the region of 4p12→q13.2. The sSMC was r(4)(p12q13.2). The fetal karyotype was 47,XX,+r(4)(p12q13.2)[17]/46,XX[19]. The pregnancy was subsequently terminated. The fetus postnatally manifested hypertelorism, epicanthic folds, a prominent nose, a triangular face, low-set ears, clinodactyly of the fingers, and small big toes. Postnatal cytogenetic analyses of fetal and extraembryonic tissues revealed the karyotypes of 47,XX,+r(4)[18]/46,XX[21] in cord blood, 47,XX,+r(4)[20]/48,XX,+r(4),+r(4)[1]/46,XX[9] in umbilical cord, 47,XX,+r(4)[14]/47,XX,+dic r(4)[1]/46,XX[25] in skin, 47,XX,+r(4)[15]/46,XX[25] in amnion, and 47,XX,+r(4)[12]/47,XX,+dic r(4)[1]/46,XX[2] in placenta.nnnCONCLUSIONnSKY, FISH, and aCGH are helpful in genetic counseling of prenatally detected sSMCs by providing the immediate and thorough information on the origin and genetic component of the sSMC.

Ventriculomegaly, Intrauterine Growth Restriction, and Congenital Heart Defects as Salient Prenatal Sonographic Findings of Miller-Dieker Lissencephaly Syndrome Associated With Monosomy 17p (17p13.2 → pter) in a Fetus

OBJECTIVEnTo present the prenatal sonographic findings of Miller-Dieker lissencephaly syndrome (MDLS) associated with monosomy 17p (17p13.2 --> pter) in a fetus.nnnCASE REPORTnA 25-year-old, gravida 3, para 1, woman was referred to Mackay Memorial Hospital at 36 weeks gestation because of ventriculomegaly, intrauterine growth restriction, and congenital heart defects detected by ultrasound. The pregnancy was uneventful until 32 weeks of gestation when ventriculomegaly was first noted. Level II ultrasound at 36 weeks gestation showed a fetal biometry equivalent to 32 weeks, tetralogy of Fallot, and bilateral ventriculomegaly. At 38 weeks gestation, a 2,308-g female baby was delivered with facial dysmorphism. A presumptive diagnosis of DiGeorge syndrome was made. However, no del22q11 could be detected by rapid fluorescence in situ hybridization analysis. Cytogenetic analysis of the cord blood revealed a 46,XX,del(17)(p13.2) karyotype. Brain ultrasound showed paucity of gyral and sulcal development. Computed tomography scans showed tetralogy of Fallot. Magnetic resonance imaging of the brain showed lissencephaly and colpocephaly. The final diagnosis was MDLS.nnnCONCLUSIONnVentriculomegaly and intrauterine growth restriction are important prenatal ultrasound markers of MDLS. Prenatal diagnosis of conotruncal heart defects in association with ventriculomegaly and intrauterine growth restriction should include a detailed investigation of MDLS in addition to DiGeorge syndrome.

Rapid aneuploidy diagnosis of partial trisomy 7q (7q34→qter) and partial monosomy 10q (10q26.12→qter) by array comparative genomic hybridization using uncultured amniocytes

OBJECTIVEnTo present rapid aneuploidy diagnosis (RAD) of partial trisomy 7q (7q34→qter) and partial monosomy 10q (10q26.12→qter) by array comparative genomic hybridization (aCGH) using uncultured amniocytes.nnnCASE REPORTnA 34-year-old, gravida 2, para 1, woman underwent amniocentesis at 20 weeks of gestation because of a previous mentally retarded child with an unbalanced reciprocal translocation inherited from the carrier father who had a karyotype of 46,XY,t(7;10) (q34;q26.12). Her first child was initially found to have a normal karyotype by routine cytogenetic analysis, but a cryptic chromosomal abnormality was subsequently diagnosed by aCGH. During this pregnancy, RAD by oligonucleotide-based aCGH using uncultured amniocytes revealed a 16.4-Mb duplication of 7q34-q36.3 and a 12.7-Mb deletion of 10q26.12-q26.3. Conventional cytogenetic analysis using cultured amniocytes revealed a karyotype of 46,XX,der(10)t(7;10)(q34;q26.12)pat. The parents elected to terminate the pregnancy. A malformed female fetus was delivered with a high prominent forehead, hypertelorism, epicanthic folds, a broad depressed nasal bridge, a prominent nose with anteverted nostrils, micrognathia, a short neck, large low-set ears, clinodactyly, small big toes, and normal female external genitalia.nnnCONCLUSIONnaCGH is a useful tool for RAD of subtle chromosomal rearrangements in pregnancy, especially under the circumstance of a previous abnormal child with an unbalanced translocation derived from a parental subtle reciprocal translocation.

PRENATAL DIAGNOSIS AND MOLECULAR CYTOGENETIC CHARACTERIZATION OF A SMALL SUPERNUMERARY MARKER CHROMOSOME DERIVED FROM CHROMOSOME 18 AND ASSOCIATED WITH A RECIPROCAL TRANSLOCATION INVOLVING CHROMOSOMES 17 AND 18

OBJECTIVEnPrenatal diagnosis of small supernumerary marker chromosomes (sSMC) gives rise to difficulties in genetic counseling, and requires molecular cytogenetic technologies such as spectral karyotyping, fluorescence in situ hybridization, multicolor-fluorescence in situ hybridization, or array-comparative genomic hybridization to identify the nature of the aberrant chromosome. We report such a case associated with a reciprocal translocation.nnnMATERIALS, METHODS AND RESULTSnA 36-year-old woman, gravida 7, para 1, abortus 5, was referred for amniocentesis at 18 weeks of gestation because of advanced maternal age. Amniocentesis revealed a reciprocal translocation between chromosomes 17q and 18q and an sSMC. The karyotype was 47,XY,t(17;18)(q11.1;q11.2), +mar. Chromosome preparations from blood lymphocytes revealed that she had the same reciprocal translocation and sSMC. Spectral karyotyping showed that the sSMC was derived from the centromeric region of chromosome 18, and there was a reciprocal translocation between chromosomes 17 and 18. The derivative chromosome 17 had positive 17p terminal (17pTEL) and chromosome 17 centromeric (cep17) signals but did not have a positive chromosome 18 centromeric signal (cep18). The derivative chromosome 18 had positive 18p terminal (18pTEL), chromosome 18 centromeric (cep18) and cep17 signals. The sSMC had only a positive cep18 signal. These findings suggested that a breakpoint occurred at 17q11.1 and another at 18q11.2 during translocation, and the sSMC originated from chromosome 18. The karyotype of the fetus was thus 47,XY,t(17;18)(q11.1;q11.2), +mar.ish der(17)t(17;18)(q11.1;q11.2)(17pTEL+,D17Z1+),der(18)t(17;18)(q11.1;q11.2)(18pTEL+,D18Z1+,D17Z1+), + der(18)(D18Z1+). Oligonucleotide-based array comparative genomic hybridization demonstrated no gain or loss of the gene dosage on chromosomes 17 and 18.nnnCONCLUSIONnOur case adds to the reported cases of sSMCs derived from the centromeric region of chromosome 18 without phenotypic consequences.

Unbalanced and Balanced Acrocentric Rearrangements Involving Chromosomes Other Than Chromosome 21 at Amniocentesis

OBJECTIVEnTo investigate unbalanced and balanced acrocentric rearrangements involving chromosomes other than chromosome 21 at amniocentesis.nnnMATERIALS AND METHODSnFrom January 1987 to September 2009, 31,194 amniocenteses were performed at Mackay Memorial Hospital, Taipei, Taiwan. Two cases with unbalanced acrocentric rearrangements involving chromosomes other than chromosome 21 from two families, and 24 cases with balanced acrocentric rearrangements involving chromosomes other than chromosome 21 from 21 families were diagnosed and investigated.nnnRESULTSnWe detected i(13q13q), +13 (one case), rob(13q14q), +13 (one case), rob(13q14q) (16 cases), rob(14q15q) (five cases), rob(13q15q) (one case), rob(15q22q) (one case), and mosaic rob(14q22q) (one case). Of the 25 cases that underwent parental cytogenetic investigation, six arose de novo and 19 were inherited (10 maternal and nine paternal). The 16 families with an inherited Robertsonian translocation included rob(13q14q) (11 families), rob(14q15q) (four families), and rob(15q22q) (one family). Of these 16 families, only two had known parental carrier status prior to the first amniocentesis, while the other 14 were aware of a parental carrier status only after prenatal diagnosis of a fetus with a heterologous Robertsonian translocation. The 18 fetuses with balanced heterologous Robertsonian translocations inherited them from six maternal carriers of rob(13q14q), four paternal carriers of rob(13q14q), four paternal carriers of rob(14q15q), and one maternal carrier of rob(15q22q). Neither UPD14 nor UPD15 was detected in any of the 16 cases tested for UPD.nnnCONCLUSIONnConcerning acrocentric rearrangements involving chromosomes other than chromosome 21, we found a frequency of 0.0064% for unbalanced rearrangements and 0.0769% for balanced rearrangements at amniocentesis in this study. rob(13q14q) was the most common and rob(14q15q) the second most common rearrangement. Of the families with an inherited translocation, 87.5% were aware of parental carrier status only after prenatal diagnosis of a fetus with a translocation by amniocentesis.

Chromosome 15q overgrowth syndrome: Prenatal diagnosis, molecular cytogenetic characterization, and perinatal findings in a fetus with dup(15)(q26.2q26.3)

OBJECTIVEnTo present molecular cytogenetic characterization of a prenatally detected duplication of 15q26.2→q26.3 in a fetus with overgrowth.nnnCASE REPORTnA 34-year-old para 0 woman underwent amniocentesis at 18 weeks of gestation because of advanced maternal age. Amniocentesis revealed a derivative chromosome 15, or der(15), with additional material at the end of the long arm of one chromosome 15. Parental karyotypes were normal. Fetal overgrowth was first noted at 21 weeks of gestation. Repeated amniocentesis was performed at 22 weeks of gestation. Array comparative genomic hybridization revealed a 4.71-Mb duplication from 15q26.2 to 15q26.3 encompassing the IGF1R gene. Fluorescence in situ hybridization analysis using the bacterial artificial chromosome clone probes specific for 15q26.2-q26.3 and the subtelomeric region of 15q showed a direct duplication and no terminal deletion in the der(15). Polymorphic DNA marker analysis determined a paternal origin of the duplication of 15q. Level II ultrasound at 23 weeks of gestation revealed a fetal biometry equivalent to 26 weeks. The pregnancy was subsequently terminated, and a 1062-g (>99(th) centile) malformed fetus was delivered at 24 weeks of gestation with craniofacial dysmorphism, craniosynostosis, and overgrowth.nnnCONCLUSIONnThe present case provides evidence for prenatal overgrowth, craniosynostosis, and characteristic facial dysmorphism in association with a duplication of 15q26.2→q26.3 and a duplication of the IGF1R gene. Prenatal diagnosis of fetal overgrowth should include a differential diagnosis of the chromosome 15q overgrowth syndrome.

Unbalanced and Balanced Heterologous Acrocentric Rearrangements Involving Chromosome 21 at Amniocentesis

OBJECTIVEnTo present unbalanced and balanced heterologous acrocentric rearrangements involving chromosome 21 at amniocentesis.nnnMATERIALS AND METHODSnBetween January 1987 and September 2009, 31,194 amniocenteses were performed at Mackay Memorial Hospital, Taipei, Taiwan. Two cases with an unbalanced heterologous acrocentric rearrangements involving chromosome 21 from two families and seven cases with balanced heterologous acrocentric rearrangements involving chromosome 21 from five families were diagnosed and investigated.nnnRESULTSnWe detected rob(14q21q),+21 (one case), rob(13q21q),+21 (one case), rob(14q21q) (four cases), rob(13q21q) (one case) and rob(15q21q) (two cases). Of the nine cases that underwent parental cytogenetic investigation, one was de novo and eight were inherited (five maternal and three paternal). The six families with an inherited acrocentric rearrangement included rob(14q21q) (three families), rob(13q21q) (two families) and rob(15q21q) (one family). Of these six families, three had a known parental carrier status before the first amniocentesis, while the other three were aware of their parental carrier status only after prenatal diagnosis of a fetus with a heterologous acrocentric rearrangement. The seven fetuses with a balanced heterologous acrocentric rearrangement were inherited from two paternal carriers of rob(14q21q), one maternal carrier of rob(14q21q), one maternal carrier of rob(13q21q), and one maternal carrier of rob(15q21q). No uniparental disomy 14 was detected in any of the three cases with rob(14q21q) tested for uniparental disomy.nnnCONCLUSIONnConcerning heterologous acrocentric rearrangements involving chromosome 21, the frequency of unbalanced rearrangements was 0.0064% and that of balanced rearrangements was 0.0224% at amniocentesis. In this study, rob(14q21q) was the most common, and rob(13q21q) and rob(15q21q) were the second most common rearrangements. Of the six families with an inherited heterologous acrocentric rearrangement involving chromosome 21, 50% (3/6) were aware of their parental carrier status only after prenatal diagnosis of a fetus with a translocation by amniocentesis.