Small supernumerary chromosome marker generating complete and pure trisomy 18p, characterized by molecular cytogenetic techniques and review

Prenatal diagnosis and molecular cytogenetic characterization of partial dup (18p)/del (18q) due to a maternal pericentric inversion 18 in a foetus with multiple anomalies

OBJECTIVE

The 18q terminal deletion with inverted duplication is an extremely rare abnormality, with only three confirmed cases in Europe to date. Here, we report, for the first time, a case of de novo 18q inv-dup-del in a Turkish pregnant woman.

CASE REPORT

A 30-year-old pregnant woman was referred for genetic analysis at her 25th gestational week due to foetal diaphragmatic hernia and rocker bottom feet. Cytogenetic analysis of the parents revealed a karyotype of 46,XX,inv(18) (p11.3q21.3) of the mother and a normal karyotype of the father. The foetal karyotype was defined as 46,XX,rec(18)del(18q)inv(18) (p11.3q21.3)mat.

CONCLUSION

To our knowledge, this is the first report of a prenatal diagnosis. Genetic counselling issues for this family, particularly affected individuals, include an increased likelihood of reduced fertility and a risk of recurrence of parental inversion equal to 1/2 in surviving offspring.

Molecular characterization of a complex small supernumerary marker chromosome derived from chromosome 18p: an addition to the literature

Background

Small supernumerary marker chromosomes (sSMC) are a heterogeneous group of structurally abnormal chromosomes, with an incidence of 0,044% in newborns that increases up to almost 7 times in developmentally retarded patients. sSMC from all 24 chromosome have been described, most of them originate from the group of the acrocentric, with around half deriving from the chromosome 15. Non-acrocentric sSMC are less common and, in the 30 percent of the cases, are associated with phenotypic effect. Complex sSMC consist of chromosomal material derived from more than one chromosome. Genotype–phenotype correlations in patients with sSMC are difficult to assess. Clinical features depend on factors such as its size, genetic content, the involvement of imprinted genes which may be influenced by uniparental disomy and the level of mosaicism. Trisomy of the short arm of chromosome 18 (18p) is an infrequent finding and does not appear to be associated with a specific syndrome. However, mild intellectual disability with or without other anomalies is reported in almost one-third of the patients.

Case presentation

Here we present clinical and molecular characterization of a new case of de novo complex sSMC consisting of the entire short arm of chromosome 18p associated with a centromere of either chromosome 13 or 21, evidenced in a 5-year-old boy during diagnostic workup for moderate intellectual disability and dysmorphisms. To date, only seven cases of isolated trisomy 18p due to a sSMC have been reported, three of which have been characterized by array CGH. In two of them the breakpoints and the size of the duplication have been described. In the manuscript we also reviewed cases reported in the DECIPHER database carrying similar duplication and also considered smaller duplications within the region of interest, in order to evaluate the presence of critical regions implicated in the pathological phenotype.

Conclusions

Our case provides additional information about phenotypic effects of pure trisomy 18p, confirms chromosomal microarray analysis as gold standard to characterize complex sSMC, and supplies additional elements for genetic counselling.

A case of childhood glaucoma with a combined partial monosomy 6p25 and partial trisomy 18p11 due to an unbalanced translocation

Background: Chromosomal deletion involving the 6p25 region results in a clinically recognizable syndrome characterized by anterior eye chamber anomalies with risk of glaucoma and non-ocular malformations (6p25 deletion syndrome). We report a newborn infant case of childhood glaucoma with a combination of partial monosomy 6p25 and partial trisomy 18p11 due to an unbalanced translocation.Materials and methods: The patient was a 0-year-old girl. Both eyes showed aniridia and left eye Peters anomaly with multiple malformations. To identify the chromosomal aberrations in the patient with clinically suspected 6p25 deletion syndrome, we performed cytogenetic analysis (G-banding and multicolor fluorescent in-situ hybridization) and array-based comparative genomic hybridization (array-CGH) analysis.Results: Cytogenetic analyses revealed a derivative chromosome 6 with its distal short arm replaced by an extra copy of the short arm of chromosome 18. Array-CGH analysis detected a 4.6-Mb deletion at 6pter to 6p25.1 and 8.9-Mb duplication at 18pter to 18p11.22. To determine the breakpoint of the unbalanced rearrangement at the single-base level, we performed a long-range PCR for amplifying the junctional fragment of the translocation breakpoint. By sequencing the junctional fragment, we defined the unbalanced translocation as g.chr6:pter_4594783delinschr18:pter_8911541.Conclusions: A phenotype corresponding to combined monosomy 6p25 and trisomy 18p11 presented as childhood glaucoma associated with non-acquired (congenital) ocular anomalies consist of aniridia and Peters anomaly and other systemic malformations. To the best of our knowledge, this is the first report which demonstrated the breakpoint sequence of an unbalanced translocation in a Japanese infant with childhood glaucoma.

Prenatal genetic analysis and differential pregnancy outcomes of two de novo cases showing mosaic isodicentric Y chromosome

Background

Fetal cells collected from the amniotic fluid of two pregnant women indicated sex chromosome abnormalities. Therefore, we performed G-banded chromosome karyotype analysis, single nucleotide polymorphism array (SNP array), fluorescence in situ hybridization (FISH), and sequence-tagged sites (STS) analysis of the Y chromosome to determine the rare molecular genetics of the two fetuses.

Case presentation

The karyotypes of the fetuses from patients 1 and 2 were mos 45,X[92]/46,X,+idic(Y)(q11.21)[8] and mos 45,X[20]/46,X,+idic(Y)(q11.223)[80], respectively. Fetus 1 had a 7.76 Mb deletion in Yq11.222q11.23 and a 15.68 Mb duplication in Yp11.2q11.21. Fetus 2 had 21 Mb of repetitive segments in Yp11.3q11.223. Azoospermia factor (AZF) detection by STS analysis revealed a missing AZFb+c region in fetus 1 and three functional AZF regions in fetus 2. The isodicentric Y chromosome (idic (Y)) in both fetuses arose de novo. The pregnancy of patient 1 was terminated, whereas the fetus of patient 2 was delivered and is now 10 months old with normal appearance and growth.

Conclusion

A combination of technologies such as chromosome karyotyping, FISH, SNP arrays, and STS analysis of the Y chromosome is important in prenatal diagnosis to reduce birth defect rates and improve the health of the Chinese population.

Prenatal detection of interstitial 18p11.31-p11.22 microduplications: Phenotypic diversity and literature review

INTRODUCTION

Pure duplication of chromosome 18p is rare, with clinical phenotypes ranging from normal or slight abnormalities to various degrees of mental retardation. It remains difficult to establish a clear genotype-phenotype correlation.

METHODS

Chromosomal karyotyping analysis was performed on cultured amniotic fluid cells from three cases. Single nucleotide polymorphism (SNP) array analysis was carried out using the Illumina Human CytoSNP-12 BeadChip. We also carried out a review of the literature regarding 18p11 microduplication.

RESULTS

G-banding analysis showed that the three cases had normal karyotypes. SNP array results showed 0.48- to 1.6-Mb microduplications of 18p11.31-p11.22 (chr18: 6995739-8713088) in these cases, encompassing different degrees of LAMA1 duplication. Follow-up analysis showed that the parents of both cases 1 and 2 chose termination of pregnancy. Case 3 presented with normal growth and physical development. Currently, there is not enough evidence supporting the pathogenicity of LAMA1 triplosensitivity.

CONCLUSION

We described three prenatal cases with 18p11.31-p11.22 microduplications involving part of the LAMA1 locus. There might be phenotypic diversity associated with 18p11.31-p11.22 microduplications. To avoid unnecessary abortions for pregnancies such as these, comprehensive genetic counseling should be offered.

Two-Generation Transmission of Trisomy 18p: Prenatal Diagnosis in a Woman with Mild Intellectual Disability

Trisomy 18p is a rarely observed chromosomal aberration. Only 31 cases have previously been described in the literature. Trisomy 18p is associated with mild to moderate phenotypic anomalies and intellectual disability. Here, we report on a pregnant woman in whom noninvasive prenatal testing indicated a high risk of fetal trisomy 18. Prenatal diagnosis and karyotyping of the parents were performed and demonstrated that both the mother and the fetus had a derivative chromosome 15 with a segment of unknown origin. Chromosomal microarray analysis and FISH revealed a 14.9-Mb duplication of 18p and detected 3 centromeres of chromosome 18. To our knowledge, this is the first study reporting trisomy 18p due to an unbalanced translocation of 18p onto chromosome 15q showing 2-generation transmission. The results suggest that trisomy 18p can be considered a euchromatic variant.

Necrotizing Enterocolitis in Two Siblings and an Unrelated Infant with Overlapping Chromosome 6q25 Deletions

The pathogenesis of necrotizing enterocolitis (NEC) remains poorly understood but is thought to be multifactorial. There are no specific recurring chromosomal abnormalities previously associated with NEC. We report 3 cases of intestinal necrosis associated with large chromosome 6 deletions. The first patient was found to have a 7.9-Mb deletion of chromosome 6 encompassing over 40 genes, arr[GRCh37] 6q25.3q26(155699183_163554531)×1. The second patient had a 19.5-Mb deletion of chromosome 6 generated by an unbalanced translocation with chromosome 18, 46,XY,der(6)t (6;18)(q25.1;p11.23), arr[GRCh37] 6q25.1q27(151639526_ 171115067)×1, 18p11.32p11.23(131700_7694199)×3, which included the whole 7.9-Mb region deleted in the first patient. The third patient was the younger sibling of the second patient with an identical derivative chromosome 6. The shared abnormal chromosome 6 region includes multiple genes of interest, particularly EZR. Mouse models have demonstrated that Ezr is expressed in microvillar epithelium and helps regulate cell-cell adhesion in the gut. We hypothesize that deletion of this shared region of 6q leads to gastrointestinal vulnerability which may predispose patients to intestinal necrosis.

Clinical, cytogenetic, and molecular outcomes in a series of 66 patients with Pierre Robin sequence and literature review: 22q11.2 deletion is less common than other chromosomal anomalies

Pierre Robin sequence (PRS) is an important craniofacial anomaly that can be seen as an isolated finding or manifestation of multiple syndromes. 22q11.2 deletion and Stickler syndrome are cited as the two most common conditions associated with PRS, but their frequencies are debated. We performed a retrospective study of 66 patients with PRS and reviewed their genetic testing, diagnoses, and clinical findings. The case series is complemented by a comprehensive literature review of the nature and frequency of genetic diagnosis in PRS. In our cohort 65% of patients had associated anomalies; of these, a genetic diagnosis was established in 56%. Stickler syndrome was the most common diagnosis, comprising approximately 11% of all cases, followed by Treacher Collins syndrome (9%). The frequency of 22q11.2 deletion was 1.5%. Chromosome arrays, performed for 72% of idiopathic PRS with associated anomalies, revealed two cases of 18q22→qter deletion, a region not previously reported in association with PRS. A review of the cytogenetic anomalies identified in this population supports an association between the 4q33-qter, 17q24.3, 2q33.1, and 11q23 chromosomal loci and PRS. We found a low frequency of 22q11.2 deletion in PRS, suggesting it is less commonly implicated in this malformation. Our data also indicate a higher frequency of cytogenetic anomalies in PRS patients with associated anomalies, and a potential new link with the 18q22→qter locus. The present findings underscore the utility of chromosomal microarrays in cases of PRS with associated anomalies and suggest that delaying testing for apparently isolated cases should be considered.

47,XY,+der(X)t(X;18)(p11.4;p11.22): A Unique Aneuploidy Associated with Klinefelter Syndrome due to an Extra Derivative X Chromosome Inherited Maternally

A derivative X chromosome formed by translocation involving an X chromosome and a chromosome 18 in a Klinefelter syndrome (KS) patient with a 47,XXY karyotype has not been reported before. In this study, we present the clinical and molecular cytogenetic characteristics. The patient presented with small testes and azoospermia. G-banding analysis identified the karyotype as 47,XY,del(X)(p?11.4). Array CGH detected a 10.36-Mb duplication of chromosome region 18p11.22p11.32 (14,316-10,377,516) and a 111.18-Mb duplication of chromosome region Xp11.4q28 (61,931, 689-155,111,583), in addition to the normal chromosome 18 and an X chromosome. FISH results further revealed the extra 18p located at the end of the short arm of a deleted X chromosome, forming a derivative X chromosome. Finally, we identified the karyotype of the patient as 47,XY,+der(X)t(X;18)(p11.4;p11.22). The derivative X chromosome was maternally inherited. To our knowledge, this rare karyotype has not yet been reported in the literature. The present study may suggest a novel karyotype associated with KS.

Azoospermia and trisomy 18p syndrome: a fortuitous association? A patient report and a review of the literature

Complete, isolated trisomy of the short arm of chromosome 18 is very rare. To date, only 24 cases of trisomy 18p have been reported in the literature, making it difficult to define a potentially associated phenotype. However, the available evidence suggests that few clinical features are shared by these patients: only variable intellectual disability, variable facial dysmorphism and epilepsy are reported in a few patients. Although three inherited cases of trisomy 18p have already been reported, all were of maternal origin.

We report on a patient carrying an isolated complete trisomy 18p translocated to the short arm of chromosome 14 and presenting with facial dysmorphism, mild intellectual disability and non-obstructive azoospermia.

Chromosomal abnormalities are more frequent in infertile men with poor sperm quality than the general population. Both numerical and structural chromosomal aberrations have been already reported within the context of azoospermia. To our knowledge, this is the first patient with trisomy 18p to present a fertility impairment due to totally altered spermatogenesis and azoospermia. Although fertility disorders were not mentioned in the four previous reports of men with trisomy 18p, none of the latter had children. We suggest that azoospermia is a previously uncharacterized feature of trisomy 18p syndrome. We further hypothesize that two mechanisms could be responsible of the fertility impairment: a meiotic synapsis defect due to the additional 18p arm that blocks meiosis, and/or overexpression of a gene located on the 18p chromosome involved in the normal testicular development.

Array-CGH analysis in Rwandan patients presenting development delay/intellectual disability with multiple congenital anomalies

Background

Array-CGH is considered as the first-tier investigation used to identify copy number variations. Right now, there is no available data about the genetic etiology of patients with development delay/intellectual disability and congenital malformation in East Africa.

Methods

Array comparative genomic hybridization was performed in 50 Rwandan patients with development delay/intellectual disability and multiple congenital abnormalities, using the Agilent’s 180 K microarray platform.

Results

Fourteen patients (28%) had a global development delay whereas 36 (72%) patients presented intellectual disability. All patients presented multiple congenital abnormalities. Clinically significant copy number variations were found in 13 patients (26%). Size of CNVs ranged from 0,9 Mb to 34 Mb. Six patients had CNVs associated with known syndromes, whereas 7 patients presented rare genomic imbalances.

Conclusion

This study showed that CNVs are present in African population and show the importance to implement genetic testing in East-African countries.

Trisomy 18p caused by a supernumerary marker with a chromosome 13/21 centromere: a possible recurrent chromosome aberration

We present a clinical and molecular cytogenetic characterization of two new patients with a complex supernumerary marker consisting of the entire short arm of chromosome 18 with a chromosome 13/21 centromere. One patient is a girl with a nonsyndromic intellectual disability and the second is a prenatally diagnosed fetus. To our knowledge, these are the fourth and fifth such cases to be described in the literature, suggesting the existence of a possible recurring constitutional structural chromosome abnormality.

Cardiac malformation of partial trisomy 7p/monosomy 18p and partial trisomy 18p/monosomy 7p in siblings as a result of reciprocal unbalanced malsegregation--and review of the literature

We report two unbalanced translocations involving the short arms of chromosomes 7 and 18 due to a balanced translocation 7;18 in the mother. Karyotyping and fluorescence in situ hybridization analysis of the female fetus revealed an unbalanced subtelomeric translocation(karyotype 46,XX,der(18)t(7;18)(p22.3;p11.32)mat resulting in a partial trisomy 7p and a partial monosomy 18p.Array comparative genomic hybridization (CGH) detected a4.44-Mb heterozygous duplication at 7p22.3 to 7p22.1 and a0.178-Mb heterozygous deletion at 18p11.32. Clinical characteristics comprised a mildly stenotic bicuspid aortic valve and a small aortic arch without coarctation. The patient's older brother displayed a reciprocal version of her chromosomal aberration (46,XY,der(7)t(7;18)(p22;p11.32) resulting in a partial monosomy 7p and a partial trisomy 18p. Array CGH revealed a 4.75-Mb heterozygous deletion at 7p22.3p22.1 and a 0.579-Mb duplication at 18p11.32. He presented with tetralogy of Fallot, cleft palate, microcephalus without craniosynostosis, growth retardation, ptosis of the right eyelid, right-sided renal agenesis, unilateral cryptorchism,and mental retardation. In this report, we present the clinical phenotype in patients with aberrations of chromosomes 7p and 18p and reviewed the literature to summarize cardiovascular malformations in these patients.

A case of partial trisomy 2p23-pter syndrome with trisomy 18p due to a de novo supernumerary marker chromosome

Partial trisomy 2p is a rare but relatively well-defined syndrome with distinctive clinical features, including marked psychomotor delay, dysmorphic face, and congenital heart disease. The phenotype of trisomy 18p is variable, from normal appearance to moderate mental retardation. Most cases of trisomy 2p and trisomy 18p result from the inheritance of an unbalanced segregant from a balanced parental translocation or due to de novo duplication. Here, we present the first report of a combined partial trisomy 2p and trisomy 18p due to a supernumerary marker chromosome (SMC). The final karyotype of the patient was 47,XX,+der(18)t(2;18)(p23.1;q11.1)[22]/46,XX[8]. The patient had typical dysmorphic features of partial trisomy 2p23-pter syndrome and congenital heart disease. SMCs are remarkably variable in euchromatic DNA content and mosaicism level. The precise identification of the origin and composition of SMCs is essential for genotype-phenotype correlation and genetic counseling.

Supernumerary marker chromosome in a child with microcephaly and mental retardation

A de novo supernumerary marker chromosome (SMC) was identified in a 13-month-old girl who presented with microcephaly and mild mental retardation. On further characterization by oligo-nucleotide array-comparative genomic hybridization [array-CGH], the SMC was confirmed to be 18p.

Trisomy 21 with a Small Supernumerary Marker Chromosome Derived from Chromosomes 13/21 and 18

We describe a trisomy 21 with a small supernumerary marker chromosome (sSMC) derived from chromosomes 13/21 and 18 in which the karyotype was 48, XY, +der(13 or 21)t(13 or 21;18)(13 or 21pter→13q11 or 21q11.1::18p 11.21→18pter),+21. Of the 35 case reports in the literature for a karyotype 48, XN, +21,+mar, in only 12 was the origin of the sSMC determined by fluorescence in situ hybridization (FISH), and only one was a der(13 or 21) and none were derived from two chromosomes. The influence of the partial trisomy 18p on the clinical outcome was hard to determine, however, there are reports on clinically healthy subjects for partial trisomy 18p.

[Strategies to identify supernumerary chromosomal markers in constitutional cytogenetics]

Supernumerary marker chromosomes (SMCs) are defined as extrastructurally abnormal chromosomes which origin and composition cannot be determined by conventional cytogenetics. SMCs are an heterogeneous group of abnormalities concerning all chromosomes with variable structure and size and are associated with phenotypic heterogeneity. The characterisation of SMCs is of utmost importance for genetic counselling. Different molecular techniques are used to identify chromosomal material present in markers such as 24-colour FISH (MFISH, SKY), centromere specific multicolour FISH (cenMFISH) and derivatives (acroMFISH, subcenMFISH), comparative genomic hybridisation (CGH), arrayCGH, and targeted FISH techniques (banding techniques, whole chromosome painting...). Based on the morphology of SMC with conventional cytogenetic and clinical data, we tried to set up different molecular strategies with all available techniques.