De novo inverted duplication 9p21pter involving telomeric repeated sequences

De Novo Duplication of Chromosome 9p in a Female Infant: Phenotype and Genotype Correlation

Trisomy 9p syndrome is the fourth most frequent chromosome aberration seen in infants. Duplication of the critical region 9p22p24 leads to mental retardation, psychomotor delay, and craniofacial and digital anomalies. We report a 2-year-old Ecuadorian girl with Trisomy 9p syndrome. Although her phenotype shares characteristics of Noonan syndrome, Giemsa trypsin banding technique shows there is an extra chromosomal segment on chromosome 14, and array analysis shows that it belongs to a duplication of 38 Mb of 9p13.1p24.3. Fluorescence in situ hybridization analysis detected three signals from 9p chromosome. The duplication is de novo, being another unique case of the few reported in the literature.

Interstitial telomeric sequences in vertebrate chromosomes: Origin, function, instability and evolution

By definition, telomeric sequences are located at the very ends or terminal regions of chromosomes. However, several vertebrate species show blocks of (TTAGGG)n repeats present in non-terminal regions of chromosomes, the so-called interstitial telomeric sequences (ITSs), interstitial telomeric repeats or interstitial telomeric bands, which include those intrachromosomal telomeric-like repeats located near (pericentromeric ITSs) or within the centromere (centromeric ITSs) and those telomeric repeats located between the centromere and the telomere (i.e., truly interstitial telomeric sequences) of eukaryotic chromosomes. According with their sequence organization, localization and flanking sequences, ITSs can be classified into four types: 1) short ITSs, 2) subtelomeric ITSs, 3) fusion ITSs, and 4) heterochromatic ITSs. The first three types have been described mainly in the human genome, whereas heterochromatic ITSs have been found in several vertebrate species but not in humans. Several lines of evidence suggest that ITSs play a significant role in genome instability and evolution. This review aims to summarize our current knowledge about the origin, function, instability and evolution of these telomeric-like repeats in vertebrate chromosomes.

Insulin-like growth factor type 1 deficiency in a Moroccan patient with de novo inverted duplication 9p24p12 and developmental delay: a case report

Background

9p duplication is a structural chromosome abnormality, described in more than 150 patients to date. In most cases the duplicated segment was derived from a parent being a reciprocal translocation carrier. However, about 15 cases with de novo 9p duplication have been reported previously. Clinically, this condition is characterized by mental retardation, short stature, developmental delay, facial dysmorphism, hand and toe anomalies, heart defects and/or ocular manifestations.

Case presentation

We report here the case of a 2-year-old Moroccan girl with a de novo duplication of 9p24 to p12. Clinical manifestations included failure to thrive, psychomotor delay, microcephaly, dysmorphic features, equinus feet, and umbilical hernia. Further clinical investigations showed an insulin-like growth factor type 1 deficiency. Banding cytogenetics identified a derivative chromosome 9, with an abnormally elongated short arm. Molecular cytogenetics based on multicolor banding probes characterized an inverted duplication 9p24 to p12 involving several genes especially an insulin-like growth factor binding protein named insulin-like growth factor binding protein-like 1, which seemed to be overexpressed, leading to the insulin-like growth factor deficiency in our patient.

Conclusions

This study showed that insulin-like growth factor type 1 deficiency can be another feature of 9p duplication, suggesting a likely involvement of insulin-like growth factor binding protein-like 1 overexpression in growth delay. However, further studies of the gene expressions are needed to better understand the phenotype-karyotype correlations.

A patient with unusual features and a 69.5 Mb duplication from a de novo extra der (9): a case report

Partial trisomy 9 is a common autosomal trisomy, which is characterized by non-specific psychomotor delay, mental retardation and moderately abnormal characteristic facial features. Generally, partial trisomy 9 leads to variable phenotypes depending on the size and position of the duplicated region. However, a precise genotype/phenotype map has not been determined. The present study reports the case of a 3-year-old female with certain typical features of trisomy 9p syndrome, who presented with a number of the distinctive symptoms, as well as sensorineural hearing loss, which has not previously been associated with this trisomy. Karyotype, M-FISH and OaCGH analysis were performed on the patient and her parents. The final karyotype was determined to be 47, XX, +mar.ish der (9) (wcp9+). arr cgh 9pterq21.12 (DOCK8→LOC138225)×3. Cytogenetic results showed a de novo extra der (9) with 69.5 Mb duplication. Although the molecular mechanism underlying the hearing loss is unclear, it was proposed that the 9q13→9q21 region may be critical for hearing.

Duplication 9p and their implication to phenotype

Background

Trisomy 9p is one of the most common partial trisomies found in newborns. We report the clinical features and cytogenomic findings in five patients with different chromosome rearrangements resulting in complete 9p duplication, three of them involving 9p centromere alterations.

Methods

The rearrangements in the patients were characterized by G-banding, SNP-array and fluorescent in situ hybridization (FISH) with different probes.

Results

Two patients presented de novo dicentric chromosomes: der(9;15)t(9;15)(p11.2;p13) and der(9;21)t(9;21)(p13.1;p13.1). One patient presented two concomitant rearranged chromosomes: a der(12)t(9;12)(q21.13;p13.33) and an psu i(9)(p10) which showed FISH centromeric signal smaller than in the normal chromosome 9. Besides the duplication 9p24.3p13.1, array revealed a 7.3 Mb deletion in 9q13q21.13 in this patient. The break in the psu i(9)(p10) probably occurred in the centromere resulting in a smaller centromere and with part of the 9q translocated to the distal 12p with the deletion 9q occurring during this rearrangement. Two patients, brother and sister, present 9p duplication concomitant to 18p deletion due to an inherited der(18)t(9;18)(p11.2;p11.31)mat.

Conclusions

The patients with trisomy 9p present a well-recognizable phenotype due to facial appearance, although the genotype-phenotype correlation can be difficult due to concomitant partial monosomy of other chromosomes. The chromosome 9 is rich in segmental duplication, especially in pericentromeric region, with high degree of sequence identity to sequences in 15p, 18p and 21p, chromosomes involved in our rearrangements. Thus, we suggest that chromosome 9 is prone to illegitimate recombination, either intrachromosomal or interchromosomal, which predisposes it to rearrangements, frequently involving pericentromeric regions.

Involvement of interstitial telomeric sequences in two new cases of mosaicism for autosomal structural rearrangements

Mosaicism for an autosomal structural rearrangement that does not involve ring or marker chromosomes is rare. The mechanisms responsible for genome instability have not always been explained. Several studies have shown that interstitial telomeric sequences (ITSs), involved in some mosaic constitutional anomalies, are potent sources of genomic instability. Here we describe two cases of mosaicism for uncommon constitutional autosomal rearrangements, involving ITSs, identified by karyotyping and characterized by FISH and SNP-array analysis. The first patient, a boy with global developmental delay, had a rare type of pure distal 1q inverted duplication (1q32-qter), attached to the end of the short arm of the same chromosome 1, in approximately 35% of his cells. The second patient, a phenotypically normal man, was diagnosed as having mosaic for a balanced non-reciprocal translocation of the distal segment of 7q (7q33qter), onto the terminal region of the short arm of a whole chromosome 12, in approximately 80% of his cells. The remaining 20% of the cells showed an unbalanced state of the translocation, with only the der(7) chromosome. He was ascertained through his malformed fetus carrying a non-mosaic partial monosomy 7q, identified at prenatal diagnosis. We show that pan-telomeric and subtelomeric sequences were observed at the interstitial junction point of the inv dup(1q) and of the der(12)t(7;12), respectively. The present cases and review of the literature suggest that the presence of ITSs at internal sites of the chromosomes may explain mechanisms of the patients's mosaic structural rearrangements.

Another rare case of a child with de novo terminal 9p deletion and co-existing interstitial 9p duplication: clinical findings and molecular cytogenetic study by array-CGH

Trisomy 9p is the fourth most common chromosome abnormality found in liveborns. We report on a rare case of partial trisomy 9p complicated by partial monosomy 9p. Clinical manifestation included craniofacial abnormalities typical for trisomy 9p syndrome, developmental delay, mental retardation and brain anomaly in the form of Dandy-Walker malformation. The cytogenetic abnormality was investigated with FISH and array-CGH to characterize the breakpoints of the complex rearrangement. The patient's karyotype was 46,XX,der(9)del(9)(p24)dup(9)(p21p24)dn.arr 9p24.3p24.2 (1-2,414,485)×1,9p24.2p21.3(2,414,485-24,101,280)×3. The cytogenetic rearrangement led to a 2.4-Mb deletion of 9p24.2pter and a 21.6-Mb duplication of 9p24.2p21.3. The clinical and cytogenetic findings in our and other similar patients are compared.

A girl with 15q overgrowth syndrome and dup(15)(q24q26.3) that included telomeric sequences

Distal 15q trisomy or tetrasomy is associated with a characteristic phenotype that includes mild to moderate intellectual disability, abnormal behavior, speech impairment, overgrowth, hyperlaxity, long face, prominent nose, puffy cheeks, pointed chin, small ears, and hand anomalies (mainly arachno- and camptodactyly). We present the case of a 13-yr-old girl with the main clinical features of 15q overgrowth syndrome and a 46,XX,dup(15)(q24q26.3)[117]/46,XX[3].ish dup(15)(q24q26.3) (SNPRN+,PML+,subtel++,tel++) de novo karyotype. The findings in this case are consistent with those in the previous distal 15q trisomy cases that presented with overgrowth and mental retardation. Further, the rearranged chromosome had a double set of directly oriented telomeric and subtelomeric sequences.

Cytogenetic and array-CGH characterization of a complex de novo rearrangement involving duplication and deletion of 9p and clinical findings in a 4-month-old female

Approximately 15 patients with partial trisomy 9p involving de novo duplications have been previously described. Here, we present clinical, cytogenetic, FISH and aCGH findings in a patient with a de novo complex rearrangement in the short arm of chromosome 9 involving an inverted duplication at 9p24→p21.3 and a deletion at 9pter→p24.2. FISH probes generated from BACs selected from the UCSC genome browser were utilized to verify this rearrangement. It is likely that some previously described duplications of 9p may also be products of complex chromosomal aberrations. This report in which FISH and aCGH were used to more comprehensively characterize the genomic rearrangement in a patient with clinical manifestations of 9p duplication syndrome underscores the importance of further characterizing cytogenetically detected rearrangements.

Molecular characterisation of a mosaicism with a complex chromosome rearrangement: evidence for coincident chromosome healing by telomere capture and neo-telomere formation

BACKGROUND

Broken chromosomes must acquire new telomeric "caps" to be structurally stable. Chromosome healing can be mediated either by telomerase through neo-telomere synthesis or by telomere capture.

AIM

To unravel the mechanism(s) generating complex chromosomal mosaicisms and healing broken chromosomes.

METHODS

G banding, array comparative genomic hybridization (aCGH), fluorescence in-situ hybridisation (FISH) and short tandem repeat analysis (STR) was performed on a girl presenting with mental retardation, facial dysmorphism, urogenital malformations and limb anomalies carrying a complex chromosomal mosaicism.

RESULTS & DISCUSSION

The karyotype showed a de novo chromosome rearrangement with two cell lines: one cell line with a deletion 9pter and one cell line carrying an inverted duplication 9p and a non-reciprocal translocation 5pter fragment. aCGH, FISH and STR analysis enabled the deduction of the most likely sequence of events generating this complex mosaic. During embryogenesis, a double-strand break occurred on the paternal chromosome 9. Following mitotic separation of both broken sister chromatids, one acquired a telomere vianeo-telomere formation, while the other generated a dicentric chromosome which underwent breakage during anaphase, giving rise to the del inv dup(9) that was subsequently healed by chromosome 5 telomere capture.

CONCLUSION

Broken chromosomes can coincidently be rescued by both telomere capture and neo-telomere synthesis.

Detection of chromosomal abnormalities by comparative genomic hybridization

PURPOSE OF REVIEW

Comparative genomic hybridization (CGH) is a modified in-situ hybridization technique. In this type of analysis, two differentially labeled genomic DNAs (study and reference) are cohybridized to normal metaphase spreads or to microarray. Chromosomal locations of copy number changes in the DNA segments of the study genome are revealed by a variable fluorescence intensity ratio along each target chromosome. Thus, CGH allows detection and mapping of DNA sequence copy differences between two genomes in a single experiment.

RECENT FINDINGS

Since its development, comparative genomic hybridization has been applied mostly as a research tool in the field of cancer cytogenetics to identify genetic changes in many previously unknown regions. It is also a powerful tool for detection and identification of unbalanced chromosomal abnormalities in prenatal, postnatal and preimplantation diagnostics.

SUMMARY

The development of comparative genomic hybridization and increase in resolution analysis by using the microarray-based technique offer new information on chromosomal pathologies and thus better management of patients.

Patient with trisomy 9p and a hypoplastic left heart with a tricentric chromosome 9

We present a patient with a hypoplastic left heart (HLH), dislocations of the hips and knees, and minor dysmorphic features, who had an abnormal karyotype that resulted in trisomy for 9p and a portion of 9q: 46,((, dic(or tri?)(9)(9pter --> 9q34::9q21 --> 9pter).ish(WCP9++).ish(D9Z5X4 +/+++). The derivative chromosome consisted of an additional copy of the proximal q arm and p arm attached to 9qter in an inverted fashion. Fluorescence in situ hybridization (FISH) using a chromosome 9 beta-satellite probe revealed three signals on the abnormal chromosome 9, suggesting the presence of 3 pericentromeric regions on the der(9). The 9q subtelomere was present on both the normal and derivative chromosome 9, suggesting that very little material, if any, is deleted.

Disclosing the mechanisms of origin of de novo short-arm duplications of chromosome 9

Three de novo short-arm duplications of chromosome 9 were investigated by fluorescence in situ hybridization (FISH) and genotyping of microsatellite loci with the aim of disclosing their mechanisms of origin. Two of these duplications were identified as direct and one as an inverted duplication, and they comprised nearly the entire 9p. In the two dirdup(9p), the distal breakpoints were mapped to subtelomeric sequences, whereas the proximal break boundaries were defined by pericentromeric sequences. The maternal origin of both duplications was demonstrated, and the presence of three different alleles in distal loci indicated that these rearrangements must have occurred prezygotically. In the invdup(9p), the proximal breakpoint was mapped at the alphoid sequences, which were partially duplicated on the tip of the rearranged 9p; subtelomeric and telomeric sequences were not detected, allowing the distal breakpoint to be mapped proximally to subtelomeric sequences. Genotyping of microsatellite loci allowed us to conclude that this invdup(9p) chromosome had a paternal origin. Homozygosity throughout the duplicated segment pointed to its probable postzygotic formation. Chromatid rearrangements appeared to have originated these 9p duplications, involving pericentromeric and subtelomeric sequences. These rearrangements might have been the result of recombination events between homologous repeats in these segments.

Loss of subtelomeric sequence associated with a terminal inversion duplication of the short arm of chromosome 4

We report on a 4(1/2)-year-old girl, who presented with multiple minor anomalies consistent with trisomy for 4p. GTG-banding identified a de novo terminal inversion duplication of distal 4p, dup(4)(p16.3p15.3). Fluorescence in situ hybridization (FISH) with a wcp4 probe confirmed the chromosome 4 origin of the additional material. FISH with a 4p subtelomere probe, D4F26, showed no signal on the dup(4) chromosome identifying a deletion of this region. Molecular analysis of 4p STS loci confirmed the subtelomeric deletion and showed loss of the paternal allele in this region. The paternal origin of the deleted region and homozygosity for one of the two paternal alleles within the region of the duplication suggests that a sister chromatid rearrangement on the paternal chromosome 4 was involved in the formation of the dup(4) chromosome. To date, the best characterized mechanisms of formation of chromosome duplications are terminal inversion duplications of 8p, which were shown to be derived from rearrangements at maternal meiosis-I. Our data show that mechanisms other than a maternal meiosis-I rearrangement can lead to the formation of terminal inversion duplications. FISH analysis with the appropriate subtelomeric probes is warranted in terminal inversion duplications to check for associated deletions.

Cytogenetic analysis from DNA by comparative genomic hybridization

Comparative genomic hybridization (CGH) is a modified in situ hybridization technique which allows detection and mapping of DNA sequence copy differences between two genomes in a single experiment. In CGH analysis, two differentially labelled genomic DNA (study and reference) are co-hybridized to normal metaphase spreads. Chromosomal locations of copy number changes in the DNA segments of the study genome are revealed by a variable fluorescence intensity ratio along each target chromosome. Since its development, CGH has been applied mostly as a research tool in the field of cancer cytogenetics to identify genetic changes in many previously unknown regions. CGH may also have a role in clinical cytogenetics for detection and identification of unbalanced chromosomal abnormalities.