A systematic analysis of small supernumerary marker chromosomes using array CGH exposes unexpected complexity
2012; Elsevier BV; Volume: 15; Issue: 1 Linguagem: Inglês
10.1038/gim.2012.78
ISSN1530-0366
AutoresKavita S. Reddy, Swaroop Aradhya, Jeanne Meck, George E. Tiller, Sridevi Abboy, Harold N. Bass,
Tópico(s)Genomics and Chromatin Dynamics
ResumoSmall supernumerary marker chromosomes (sSMCs) are chromosomal fragments or markers whose origins often cannot be determined by conventional cytogenetic methods alone and require molecular approaches for definitive characterization. sSMCs are, in general, equal in size or smaller than a chromosome 20 of the same metaphase spread. Complex SMCs are composed of noncontiguous DNA or amplicons. SMCs are found in ~0.043% of live births and ~0.075% prenatal cases and are seven times more prevalent in intellectually disabled patients.1.Liehr T. Weise A. Frequency of small supernumerary marker chromosomes in prenatal, newborn, developmentally retarded and infertility diagnostics.17390076Int J Mol Med. 2007; 19: 719-731Google Scholar Approximately 77% of SMCs are de novo and 23% are inherited, either from the mother (16%) or the father (7%). A ring-like SMC occurs with a frequency of 0.14–0.72/1,000 in newborns and 0.14–1.5/1,000 in prenatal diagnoses.2.Graf M.D. Christ L. Mascarello J.T. Redefining the risks of prenatally ascertained supernumerary marker chromosomes: a collaborative study.1:STN:280:DC%2BD28vlvFOhsQ%3D%3D10.1136/jmg.2005.037887J Med Genet. 2006; 43: 660-664Google Scholar Most SMCs (70%) are derived from the short arms and pericentromeric regions of acrocentric chromosomes. Those derived from nonacrocentric autosomes are rare and occur with a frequency of ~15% of all markers.3.Stankiewicz P. Bocian E. Jakubów-Durska K. Identification of supernumerary marker chromosomes derived from chromosomes 5, 6, 19, and 20 using FISH.1:STN:280:DC%2BD3c7jtVegtQ%3D%3D10.1136/jmg.37.2.114J Med Genet. 2000; 37: 114-120Google Scholar Markers that are not derived from acrocentric chromosomes are often suspected to be small ring chromosomes on the basis of their morphology and behavior.4.Baldwin E.L. May L.F. Justice A.N. Martin C.L. Ledbetter D.H. Mechanisms and consequences of small supernumerary marker chromosomes: from Barbara McClintock to modern genetic-counseling issues.1:CAS:528:DC%2BD1cXit1Sju7Y%3D10.1016/j.ajhg.2007.10.013Am J Hum Genet. 2008; 82: 398-410Google Scholar Whole-genome array-based comparative genomic hybridization (aCGH) and fluorescence in situ hybridization (FISH) can now provide accurate characterization of SMCs in terms of chromosomal origin, gene content, uniparental disomy, and other concomitant imbalances elsewhere in the genome. Without the benefit of aCGH, the empiric risk of phenotypic abnormalities associated with a prenatally detected de novo SMC is 18% if it contains satellites and 31% if it does not have satellite sequences.2.Graf M.D. Christ L. Mascarello J.T. Redefining the risks of prenatally ascertained supernumerary marker chromosomes: a collaborative study.1:STN:280:DC%2BD28vlvFOhsQ%3D%3D10.1136/jmg.2005.037887J Med Genet. 2006; 43: 660-664Google Scholar This risk depends on a number of factors, including ultrasound findings, whether the SMC is familial, and if it is associated with a known syndrome. Certain marker chromosomes are consistently identifiable by G-banding and have a well-established phenotype. Examples include isochromosome 12p, associated with Pallister–Killian syndrome (OMIM 601803) and isochromosome 18p, which causes mild–moderate mental retardation and a characteristic facial appearance.5.Callen D.F. Freemantle C.J. Ringenbergs M.L. The isochromosome 18p syndrome: confirmation of cytogenetic diagnosis in nine cases by in situ hybridization.1:STN:280:DyaK3czmsFSnsA%3D%3D23930231683854Am J Hum Genet. 1990; 47: 493-498Google Scholar For chromosome 15-derived marker chromosomes, often seen as isodicentric 15q, FISH analysis allows discrimination between large markers that contain the SNRPN locus (OMIM 182279) and are tetrasomic for the Prader–Willi syndrome (OMIM 176270) or Angelman syndrome (OMIM 105830) critical region and those small markers that do not contain SNRPN. Based on the parental origin, the larger markers are known to cause a phenotype involving some combination of mental retardation, seizures, autistic features, and growth retardation, whereas the latter are usually associated with a normal phenotype.6.Crolla J.A. Harvey J.F. Sitch F.L. Dennis N.R. Supernumerary marker 15 chromosomes: a clinical, molecular and FISH approach to diagnosis and prognosis.1:STN:280:DyaK2M7mtl2gsA%3D%3D10.1007/BF00209395Hum Genet. 1995; 95: 161-170Google Scholar,7.Huang B. Crolla J.A. Christian S.L. Refined molecular characterization of the breakpoints in small inv dup(15) chromosomes.1:CAS:528:DyaK2sXhtV2ms70%3D10.1007/s004390050301Hum Genet. 1997; 99: 11-17Google Scholar,8.Eggermann K. Mau U.A. Bujdosó G. Supernumerary marker chromosomes derived from chromosome 15: analysis of 32 new cases.10.1034/j.1399-0004.2002.620113.xClin Genet. 2002; 62: 89-93Google Scholar Similarly, FISH analysis of chromosome 22–derived markers can reveal whether the SMCs contain the critical region for cat eye syndrome (OMIM 115470), which is characterized by ocular coloboma and other dysmorphic features.9.Mears A.J. el-Shanti H. Murray J.C. McDermid H.E. Patil S.R. Minute supernumerary ring chromosome 22 associated with cat eye syndrome: further delineation of the critical region.1:STN:280:DyaK2MzpslymsQ%3D%3D76682961801256Am J Hum Genet. 1995; 57: 667-673Google Scholar However, our knowledge on the clinical significance of the other sSMCs is limited. Although complex markers are estimated to form only a small percentage (~0.9%) of SMCs,10.Trifonov V. Fluri S. Binkert F. Complex rearranged small supernumerary marker chromosomes (sSMC), three new cases; evidence for an underestimated entity.Mol Cytogenet. 2008; 15: 1-6Google Scholar this may be an underestimation as highlighted in two recent studies applying aCGH to SMCs.11.Vetro A. Manolakos E. Petersen M.B. Unexpected results in the constitution of small supernumerary marker chromosomes.10.1016/j.ejmg.2012.01.010Eur J Med Genet. 2012; 55: 185-190Google Scholar,12.Yu S. Fiedler S.D. Brawner S.J. Joyce J.M. Zhou X.G. Liu H.Y. Characterizing small supernumerary marker chromosomes with combination of multiple techniques.1:STN:280:DC%2BC387ns1WitA%3D%3D10.1159/000334271Cytogenet Genome Res. 2012; 136: 6-14Google Scholar To address the frequency of complex markers and to provide prognosis based on a meaningful genotype-to-phenotype correlation, we took a systematic, comprehensive approach to precisely characterize 10 consecutive SMCs using chromosome analysis, aCGH, and FISH. Whole-genome aCGH was performed using a custom-designed oligonucleotide array with ~180,000 probes. The nonrepetitive sequence of the human genome was covered with probes spaced 35 kb apart, on average. More than 200 clinically significant regions had a higher probe density with 250 bp–5 kb probe spacing. The array was designed based on human genome build hg19/GRCh37. For the aCGH, 0.5 µg of patient DNA was labeled with Cy5 dye and a sex-matched reference DNA (Promega, Madison, WI) was labeled with Cy3 dye. After purification, the labeled products were combined and hybridized to the custom array for 40 h at 65 °C. The arrays were washed and scanned on a 3-μm scanner to obtain a TIFF image. This image was imported into Feature Extraction software to quantify the fluorescence data. The resulting data were imported into Agilent Genomic Workbench 6.5.0.25 software for visualization of copy number genome-wide. FISH using custom-labeled BAC probes (Empire Genomics, Buffalo, NY) and commercial centromeric probes (Abbott Molecular, Des Plaines, IL) was performed following the standard protocol. For those cases in which genotyping was performed to assess parental origin of the sSMC, we used an array that contained the same probes for copy-number analysis and also 66,480 oligonucleotide probes that contained single-nucleotide polymorphisms. These single-nucleotide polymorphisms were assayed for zygosity by cutting with AluI and RsaI restriction enzymes. The DNA (0.5 µg) from the patient and from a sex-matched HapMap sample (European) was digested with AluI and RsaI for 3 h. The digested fragments were purified, labeled, and arrays processed as described earlier. The IRB approval can be found in Supplementary material online. Table 1 summarizes the results from the systematic use of conventional cytogenetic banding methods (G, C, and AgNOR), aCGH analysis, and FISH studies. The morphology of sSMC from the banding methods and precise genomic content defined by aCGH analysis determined the FISH probes necessary for the complete characterization of the marker. Based on our findings, the markers are classified into three groups: marker unidentified by aCGH, simple marker, and complex marker.Table 1Summary of cytogenetic, FISH, and array CGH results Case 1. Figure 1a represents a small mosaic bisatellited marker present in 93% of cells by G-banding, which was not detected by aCGH. Therefore, this marker was assumed to lack euchromatin. About two-thirds of reported sSMCs were derived from acrocentric chromosomes; almost 70% of those acrocentric-derived sSMC were inverted duplications or dicentric derivatives without euchromatin and were transmitted through several generations in some families.13.Liehr T. sSMC homepage. 2005. http://www.med.uni-jena.de/fish/sSMC/00START.htm.Google Scholar Case 2. (Figure 1b) A mosaic (13.3%), small, nonsatellited, ring-like marker chromosome with euchromatin was not detected by aCGH or spectral karyotyping. Case 3. (Figure 1c) Two cell lines were present: one with a marker 1 in 37% cells and the other with markers 1 and 2 in 13.3% cells, but neither were detected by aCGH. Marker 1 was C-band- and AgNOR-positive, and marker 2 was only C-band-positive and ring-like. Case 4. (Figure 1d) A mosaic (12%), nonsatellited, ring-like marker with a centromere was not detected by aCGH. Markers in cases 2–4 may not have been detected by aCGH because of the low percentage of cells with the marker. Case 5. (Figure 2) A mosaic (50%), de novo, small, nonsatellited marker chromosome that appeared ring-like in G- and C-banding was found in a patient with developmental and speech delay. aCGH showed a gain of 23.1 Mb in ~30% of cells for the region 5p13.3q11.2 (chr5:32,731,799–55,802,261). By FISH analysis, probe RP11-977H15 [5p13.1] localized to the supernumerary marker in 48% of metaphases and gave an additional signal in 36% of interphases. The marker included the reported 5p13 duplication syndrome (OMIM 613174) associated with developmental delay, mental retardation in all patients, and other features in some patients, while 5q11 trisomy has been associated with learning difficulties and speech delay.14.Melo J.B. Backx L. Vermeesch J.R. Chromosome 5 derived small supernumerary marker: towards a genotype/phenotype correlation of proximal chromosome 5 imbalances.10.1007/s13353-011-0035-3J Appl Genet. 2011; 52: 193-200Google Scholar Case 6. (Figure 2) aCGH showed a de novo 14.2 Mb gain of the short arm of chromosome 18p11.32p11.21 in a patient with global developmental delay, mental retardation, and up-slanting palpebral fissures. A G-band SMC was monosatellited, positive for silver staining, and negative for 18-centromere FISH probe. Hence, the SMC was derived from a translocation between an acrocentric chromosome (other than chromosome 15) and chromosome 18 short arm (18ptel-positive by FISH). Trisomy of the 18p arm causes variable intellectual disability, developmental delay, minor facial dysmorphism, and other anomalies.15.Schinzel A. Catalogue of Unbalanced Chromosome Aberrations in Man, 2nd edn. DeGruyter: New York, 2001.Google Scholar In addition, our proband had a maternally inherited 14 kb deletion in the KCNQ1 gene on 11p25.5. Mutations in KCNQ1 cause long QT syndrome (OMIM 192500).16.OMIM (Online Mendelian inheritance in man). Johns Hopkins University, Center for Medical Genetics: Baltimore, 1996. http://omim.org/entry/192500.Google Scholar,17.GeneReviews. http://www.genetests.org.Google Scholar Although the deletion included the first exon of the KCNQ1 gene in the minor transcript NM_181798, the expression pattern and prevalence of this transcript are unknown. In the commonly used reference transcript for KCNQ1, NM_000218, the small deletion falls within an intron.18.Inherited arrhythimas database. http://www.fsm.it/cardmoc/,Human Genome Mutation Database; https://portal.biobaseinternational.com/hgmd/pro/search_gene.php?.Google Scholar These results were also confirmed by targeted exon-level aCGH. The maternal sample showed the 11p25.5 deletion and normal copy number for 18p11. The paternal sample showed normal results for both genomic regions. The clinical significance of the deletion within KCNQ1 is currently unknown. Case 7. (Figure 2) A de novo, satellited, mosaic (37%) sSMC had a C-band and was AgNOR-positive. aCGH showed a mosaic (20%) 5.2 Mb gain of chromosome 19p13.2p13.12. This gain was shown to be present on the sSMC using probes RP11-360D23 and RP11-360D23 that map to chromosome 19p13.2. The marker was shown to be derived from chromosome 14 by FISH using the RP11-692L20 [14q11.1] probe and was shown to be negative for the D19Z3 centromere probe. FISH analysis detected mosaicism for the marker in 28% of metaphases and in 41% of interphases. This 5.2 Mb genomic region contains a large number of genes, including several that are associated with clinical disorders. OMIM-listed genes in this interval are TYK2, DNM2, LDLR, EPOR, PRKCSH, MAN2B1, RNASEH2A, GCDH, LYL1, CACNA1, and CC2D1A. The proband, with developmental delay, was in fourth-grade special education and had speech therapy for difficulty with language, such as putting words together. She was unable to state her birthday. A review of systems revealed absence of seizures. Physical examination showed the following results: blood pressure 119/60; pulse 83; height 1.165 m (3 feet 9.87 inches); weight 26.4 kg (58 lb 3.2 oz), and head circumference 49 cm. Growth percentiles based on body mass index for age, stature for age, and OFC for age were 85.13% (19.45 kg/(m2)),0.11% (50% for 6.5 years) and 20%, respectively. Facial features were remarkable for periorbital fullness (similar to parents), somewhat arched eyebrows, mild synophrys, somewhat smooth philtrum, and prominent ears with attached lobes. Skin was without rashes, lesions, or stria distensae. Of note were short stature and developmental delay. However, both parents and siblings were short. The parents were of advanced age when the proband was conceived. The reported phenotype associated with gains that include the chromosome 19p13.2p13.12 region (chr19:9,647,931–14,875,098) is summarized in Supplementary Table S1, online. A nonmosaic duplication involving the 19p13.2p13.13 genomic region was described in an individual with developmental delay, microcephaly, heart defects, and multiple minor anomalies.19.Stratton R.F. DuPont B.R. Olsen A.S. Fertitta A. Hoyer M. Moore C.M. Interstitial duplication 19p.1:STN:280:DyaK28%2FivVKrtw%3D%3D10.1002/ajmg.1320570409Am J Me.d Genet. 1995; 57: 562-564Google Scholar Another 12-month-old infant was evaluated for severe hypotonia, psychomotor retardation, and facial dysmorphisms that included round face, high prominent forehead, downward-slanted palpebral fissures, hypertelorism, short nose, chubby cheeks, long philtrum, anteverted lower lip, and low-set asymmetric and dysmorphic ears. Karyotype analysis disclosed an extra mosaic ring chromosome, which included the whole 19p arm.20.Novelli A. Ceccarini C. Bernardini L. Pure trisomy 19p syndrome in an infant with an extra ring chromosome.1:STN:280:DC%2BD2MvjsFGjtA%3D%3D10.1159/000086391Cytogenet Genome Res. 2005; 111: 182-185Google Scholar The clinical finding in one patient with an SMC for chromosome 19p was developmental delay.21.Liehr T. sSMC homepage. 2006. http://www.med.unijena.de/fish/ssmc/00start.htm.Google Scholar A 9-year-old boy with psychomotor retardation had a small mosaic sSMC. The karyotype was interpreted as: 47,XY,+mar.ish der(19)(:p13.3→p11:)(839B1+, 872G3+,728C8+, D1/5/19Z+)dn[52]/46,XY[48].22.Vranekovic J. Brajenovic-Milic B. Modrusan-Mozetic Z. Babic I. Kapovic M. Severe psychomotor retardation in a boy with a small supernumerary marker chromosome 19p.1:STN:280:DC%2BD1crntF2ksw%3D%3D10.1159/000138902Cytogenet Genome Res. 2008; 121: 298-301Google Scholar A microduplication for 19p13.2 (chr19:9,109,407–11,068,542) by aCGH presented with variable neurocognitive disability, overgrowth, and facial dysmorphism similar to Sotos syndrome. Increased expression of duplicated genes ILF3 (interleukin enhancer-binding factor 3), ZNF266 (zinc finger protein 266), DNMT1 (DNA methyltransferase gene 1), and SMARCA4 (Swi/Snf-related, matrix-associated, actin-dependent regulator of chromatin, subfamilyA, member 4) in peripheral blood, seen by whole-genome expression array transcript level and quantitative PCR, supported gene dosage as the cause for this disorder.23.Lehman A.M. du Souich C. Chai D. 19p13.2 microduplication causes a Sotos syndrome-like phenotype and alters gene expression.1:CAS:528:DC%2BC38XhsVKgsrg%3D10.1111/j.1399-0004.2010.01615.xClin Genet. 2012; 81: 56-63Google Scholar Case 8. (Figure 3) A de novo sSMC was C-band-positive and AgNOR-negative. aCGH displayed gains in 19q12q13.12 (chr19:30,735,448–36,120,396) of ~5.4 Mb in size and in 19q13.2q13.31 (chr19: 42,891,150–43,922,624) of ~1 Mb in size. The chromosome 19 centromere and both gains were shown to be on the marker by FISH using D19Z3, RP11-671P13 [19q13.1], and RP11-9 80G2 [19q13.2] probes. A child born to parents of advanced age was seen for developmental delay and obesity. The patient started walking at 9 months, spoke the first word at 6 months, began using sentences at 18 months, and was toilet trained. There was a history of regression. At 3 years of age, he was diagnosed with autism and has not been re-evaluated. He reportedly has an individual education program/plan and was in the second grade, receiving speech therapy every day for 30 min and adaptive physical education. On examination, the proband was friendly and made good eye contact. Speech impairment was observed when his brother was born (around 18 months of age) and then again at around 4 years of age. He has been in special education since kindergarten and can recognize a few letters of the alphabet and reportedly can do basic math. There is no family history of problems similar to the patient's condition. Physical examination showed 99.28% of growth percentile based on weight for age (+3 SD above the mean) and occipitofrontal circumference of 53 cm (75%). Habitus was obese. He had upswept anterior hairline, low posterior hairline, and a widow's peak. Mid-occipital flatness, up-slanted palpebral fissures, and medially sparse eyebrows were also present. Other features were widely spaced teeth, smooth philtrum, thin upper lip, a short neck, and gynecomastia. Bilaterally, thumbs were short; he also had short fifth fingers with clinodactyly, brachydactyly, and tapered fingers. Fetal fat pads were present. He had developmental delay, speech difficulties, and hyperactivity. Quack et al.24.Quack B. Van Roy N. Verschraegen-Spae M.R. Klein F. Interstitial deletion and ring chromosome derived from 19q. Proximal 19q trisomy phenotype.1:STN:280:DyaK3s3gslersw%3D%3D1296524Ann Genet. 1992; 35: 241-244Google Scholar reported a supernumerary ring chromosome derived from the proximal part of the long arm of chromosome 19 [47,XY,+ r(19)(q11–q13.2)]. The patient presented with mental retardation and macrocephaly, and weight was reported to be three standard deviations above the mean. He was born small for gestational age, and had some dysmorphic features (hypertelorism, anti-Mongolian slants, and minor nose and mouth malformations). His mother and sibling were normal and carried the same ring chromosome but had a balanced karyotype with an interstitial deletion of the long arm of chromosome 19. Zung et al.25.Zung A. Rienstein S. Rosensaft J. Aviram-Goldring A. Zadik Z. Proximal 19q trisomy: a new syndrome of morbid obesity and mental retardation.1:CAS:528:DC%2BD2sXisVCqtLo%3D17057406Horm Res. 2007; 67: 105-110Google Scholar described a 13-year-old with a marker consisting of 19q12q13.2, constitutional obesity, mental retardation, and dysmorphic features. Because this region contains several genes that are related to adipose tissue homeostasis and insulin resistance, several metabolic comorbidities such as insulin resistance, dislipidemia, and hyperuricemia may be associated with this syndrome. The morbid obesity observed began as overweight, but from 5 years there was rapid gain in body weight, although the patient was not hyperphagic. Davidsson et al.26.Davidsson J. Jahnke K. Forsgren M. dup(19)(q12q13.2): array-based genotype–phenotype correlation of a new possibly obesity-related syndrome.10.1038/oby.2009.298Obesity. 2010; 18: 580-587Google Scholar presented a girl with two supernumerary marker chromosomes causing a duplication of 19q12q13.2, with delayed developmental milestones, corpus callosum anomalies, microphthalmia, and obesity. The 19q segment contained the genes AKT2, CEACAM1, CEBPA, LIPE, and TGFB1, which are involved in adipose tissue homeostasis and insulin resistance and that could potentially have contributed to the obese phenotype observed. Hall et al.27.Hall C.E. Cunningham J.J. Hislop R.G. Berg J.N. A boy with supernumerary mosaic trisomy 19q, involving 19q13.11-19q13.2, with macrocephaly, obesity and mild facial dysmorphism.10.1097/MCD.0b013e32833bff06Clin Dysmorphol. 2010; 19: 218-221Google Scholar also described a patient who had obesity and macrocephaly and a supernumerary de novo mosaic marker involving cytoband 19q13.11q13.2. Our obese proband also has gains of CEACAM1, CEBPA, LIPE genes due to the SMC. This obesity-associated genetic syndrome could have implications in the management and treatment of patients with a duplication of 19q12q13.2. Case 9. (Figure 3) High-resolution chromosome analysis on peripheral blood revealed a 46,XX karyotype in 10%, 47,XXX in 10%, and a nonsatellited sSMC in 80% of cells. The karyotype was mos47,XXX[2]/47,XX, +mar[17]/46,XX[2]. Parental chromosome analysis showed a 46,XY[50] complement in the father and low-grade 45,X (6%) mosaicism in the mother, who was of advanced maternal age. Neither parent was found to carry a marker chromosome. Prenatal chromosome analysis on amniotic fluid was reported as normal; these slides were re-evaluated and the marker was identified. aCGH showed a complex set of rearrangements involving chromosome 20. The first imbalance was a 2.6 Mb deletion of virtually the entire 20p12.2 band; the second imbalance was a 2.6 Mb duplication of 20p12.2p12.1; the third was a 634 kb duplication in 20p12.1; and the final imbalance was a 2.6 Mb duplication of the pericentromeric region of the long arm of chromosome 20q11.21. Mosaicism was not evident for any of the copy-number changes. When polymorphic markers were informative, genotype analysis showed only paternal alleles in the deleted segment and extramaternal alleles within the duplicated segments. Metaphase FISH performed on 25 cells with probes targeted to 20p12.1 (RP11-426N21), 20p12.2 (RP11-2E8), 20q11.21 (RP11-822E15), and the centromere (D20Z1) showed that this patient carries a derivative chromosome 20 with a deletion in 20p12.2 (RP11-2E8) and tandem duplication 20p12.2–20p12.1 (RP11-426N21). The latter was confirmed in interphase FISH. In addition, the supernumerary marker chromosome showed a chromosome 20 centromere (D20Z1) and the pericentromeric region of 20q11.21 (RP11-822E15), which corresponded to the 2.6 Mb gain detected by aCGH. The deletion in 20p12.2 affects seven genes, including JAG1. Haploinsufficiency for JAG1 causes Alagille syndrome, which involves posterior embryotoxon in the eyes, bile duct paucity, congenital heart defects, butterfly vertebrae, typical facies, and other anomalies.16.OMIM (Online Mendelian inheritance in man). Johns Hopkins University, Center for Medical Genetics: Baltimore, 1996. http://omim.org/entry/192500.Google Scholar,17.GeneReviews. http://www.genetests.org.Google Scholar,28.Oda T. Elkahloun A.G. Meltzer P.S. Identification of a larger than 3 Mb deletion including JAG1 in an Alagille syndrome patient with a translocation t(3;20)(q13.3;p12.2).1:STN:280:DC%2BD3cvhtFSqtA%3D%3DHum Mutat. 2000; 16 (10.1002/1098-1004(200007)16:1 3.0.CO;2-4): 92Google Scholar In addition to JAG1, MKKS is deleted in our patient. Mutations in MKKS lead to autosomal recessive McKusick–Kaufman syndrome (OMIM 236700) or Bardet–Biedl syndrome type 6 (OMIM 209900). The 2.6 Mb duplication in 20p12.2p12.1 affects eight genes. Among these, C20orf7 is associated with autosomal recessive mitochondrial complex I deficiency (OMIM 252010), and the others are not known to be clinically relevant at present. Sections of this 2.6 Mb genomic region are reported to vary in copy number in the normal population. The 634 kb duplication in 20p12.1 is a likely benign copy-number change because it affects only the MACROD2 and KIF16B genes; these genes are not known to be clinically significant and parts of their sequences are reported to vary in copy number in the normal population.29.Database of Genomic Variants. http://projects.tcag.ca/variation.Google Scholar The last genomic imbalance in this patient is a 2.6 Mb duplication of 20q11.21 in the pericentromeric region of the long arm that corresponds to the marker identified in this patient's karyotype. This duplicated region contains more than 35 genes, including a cluster of the DEFB (defensin) genes. This particular duplication has not been previously described, but a larger duplication, 20q11.21q12, has been reported to result in psychomotor retardation, craniofacial anomalies, and a severe vision deficit.30.Wanderley H.Y. Schrander-Stumpel C.T. Visser M.O. Van Maanen-Op Het Roodt E.A. Loneus W.H. Engelen J.J. Report of a patient with a trisomy of chromosome region 20q11.2-->20q12 and characterization with FISH.1:STN:280:DC%2BD2MrotFOmsg%3D%3D16259325Genet Couns. 2005; 16: 277-282Google Scholar A second report describes a supernumerary chromosome 20 with material from 20p11.21 to 20q11.21 in a patient with a normal phenotype and obesity.31.Guediche N. Brisset S. Benichou J.J. Chromosomal breakpoints characterization of two supernumerary ring chromosomes 20.10.1002/ajmg.a.33250Am J Med Genet A. 2010; 152: 464-471Google Scholar Our proband was born to a nonconsanguineous couple of advanced parental age. The couple's only other pregnancy together was electively terminated for fetal hydrocephalus; amniocentesis revealed a normal karyotype. In addition, through a previous relationship, the mother had two healthy offspring. During the proband's pregnancy, the mother was treated with insulin for gestational diabetes. There was poor fetal growth in the third trimester, but maternal titers for cytomegalovirus, herpes simplex, rubella, syphilis, and toxoplasmosis were negative. A cesarean section was performed at 35 weeks' gestation for intrauterine growth restriction and oligohydramnios. The infant weighed 1,995 g (10th centile), was 39.5 cm long (less than third centile), and had a 30.5-cm head circumference (10th centile). There were three pedunculated, preauricular skin tags on the left. Cranial and renal ultrasound studies were normal. The infant passed newborn screening and was discharged on day 8. A heart murmur due to pulmonary valvular stenosis was detected at 2 weeks of age. The infant underwent a percutaneous pulmonary valvuloplasty at 6 weeks of age. When examined at 8 months of age, weight, length, and head circumference were symmetrically below the second centile. The forehead was broad, previously described preauricular tags were present, ears were borderline low-set with over-folded helices and a deep vertical groove behind the right ear helix, the nasal bridge was broad, the upper lip was thin with a slightly downturned mouth and normal palate, and a grade 3 of 6 harsh systolic murmur could be heard over the precordium. Tone was increased without scissoring. The infant reached for toys, used consonants, and imitated sounds, but was unable to roll over from the back to the abdomen and could only sit when brought into position. There was no jaundice or hepatomegaly, and the parents reported normal stools. Eye examination by a pediatric ophthalmologist revealed no posterior embryotoxon or other anomalies. Liver enzymes and bilirubin were normal. Spine films demonstrated butterfly-type vertebrae T10 and T11. X-rays of the chest and ribs were normal. Supernumerary marker/ring chromosome 20 is a rare abnormality and no common phenotype has been described. Because the majority of previous reports of extra marker/ring 20 have not been sized, a genotype–phenotype relation is difficult to establish. Guediche et al.31.Guediche N. Brisset S. Benichou J.J. Chromosomal breakpoints characterization of two supernumerary ring chromosomes 20.10.1002/ajmg.a.33250Am J Med Genet A. 2010; 152: 464-471Google Scholar reviewed the supernumerary ring chromosome 20 and surmised varying degrees of phenotypic abnormality. Among these descriptions, the most frequently noted manifestations were growth and psychomotor retardation, low-set ears, hand and foot anomalies, and micrognathia.32.Callen D.F. Eyre H.J. Ringenbergs M.L. Freemantle C.J. Woodroffe P. Haan E.A. Chromosomal origin of small ring marker chromosomes in man: characterization by molecular genetics.1:STN:280:DyaK3M7ps1OgtA%3D%3D20148001682952Am J Hum Genet. 1991; 48: 769-782Google Scholar,33.Blennow E. Annerén G. Bui T.H. Berggren E. Asadi E. Nordenskjöld M. Characterization of supernumerary ring marker chromosomes by fluorescence in situ hybridization (FISH).1:STN:280:DyaK3szhvVynsQ%3D%3D83284591682354Am J Hum Genet. 1993; 53: 433-442Google Scholar,34.Batista D.A. Escallon C. Blakemore K.J. Stetten G. An accessory marker
Referência(s)